TransAlta Corporation (SEC Filing Page | XBRL Cloud Viewer | XBRL Instance)

Line	Label	Object Class	Period Type	Balance	Report ElementName
1	0001000 - Document - Document and Entity Information Document	Network	*	*	http://www.transalta.com/role/DocumentAndEntityInformationDocument
2	Implied Table	Table	*	*	implied:Table
3	Document And Entity Information [Abstract]	Abstract			tac:DocumentAndEntityInformationAbstract
4	Document Type	Concept (Submission Type)	For Period		dei:DocumentType
5	Document Period End Date	Concept (Date)	For Period		dei:DocumentPeriodEndDate
6	Amendment Flag	Concept (Yes/No)	For Period		dei:AmendmentFlag
7	Entity Registrant Name	Concept (Text/String)	For Period		dei:EntityRegistrantName
8	Entity Central Index Key	Concept (CIK Number)	For Period		dei:EntityCentralIndexKey
9	Entity Current Reporting Status	Concept (Yes/No)	For Period		dei:EntityCurrentReportingStatus
10	Current Fiscal Year End Date	Concept (Month/Day)	For Period		dei:CurrentFiscalYearEndDate
11	Document Fiscal Year Focus	Concept (Year)	For Period		dei:DocumentFiscalYearFocus
12	Document Fiscal Period Focus	Concept (Fiscal Period)	For Period		dei:DocumentFiscalPeriodFocus
13	Entity Common Shares Outstanding	Concept (Shares)	As Of		dei:EntityCommonStockSharesOutstanding
14	Entity Public Float	Concept (Monetary)	As Of	Credit	dei:EntityPublicFloat
15	1001000 - Statement - Consolidated Statements of Earnings (Loss) Statement	Network	*	*	http://www.transalta.com/role/ConsolidatedStatementsOfEarningsLossStatement
16	Implied Table	Table	*	*	implied:Table
17	Profit or loss [abstract]	Abstract			ifrs-full:IncomeStatementAbstract
18	Revenues (Note 5)	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromContractsWithCustomers
19	Fuel and purchased power (Note 6)	Concept (Monetary)	For Period	Debit	ifrs-full:CostOfSales
20	Gross margin	Concept (Monetary)	For Period	Credit	ifrs-full:GrossProfit
21	Operations, maintenance and administration (Note 6)	Concept (Monetary)	For Period	Debit	ifrs-full:GeneralAndAdministrativeExpense
22	Depreciation and amortization	Concept (Monetary)	For Period	Debit	ifrs-full:DepreciationAndAmortisationExpense
23	Asset impairment charges (reversals) (Note 7)	Concept (Monetary)	For Period	Debit	ifrs-full:ImpairmentLossReversalOfImpairmentLossRecognisedInProfitOrLoss
24	Taxes, other than income taxes	Concept (Monetary)	For Period	Debit	ifrs-full:TaxExpenseOtherThanIncomeTaxExpense
25	Net other operating expense (income) (Note 9)	Concept (Monetary)	For Period	Credit	ifrs-full:OtherOperatingIncomeExpense
26	Operating income	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossFromOperatingActivities
27	Finance lease income	Concept (Monetary)	For Period	Credit	ifrs-full:FinanceIncomeOnNetInvestmentInFinanceLease
28	Net interest expense (Note 10)	Concept (Monetary)	For Period	Debit	ifrs-full:InterestExpense
29	Foreign exchange gain (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnExchangeDifferencesOnTranslationRecognisedInProfitOrLoss
30	Gain on sale of assets and other	Concept (Monetary)	For Period	Credit	ifrs-full:GainsOnDisposalsOfNoncurrentAssets
31	Earnings (loss) before income taxes	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossBeforeTax
32	Income tax expense (recovery) (Note 11)	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
33	Net earnings (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
34	Net earnings (loss) attributable to:	Abstract			ifrs-full:ProfitLossAttributableToAbstract
35	TransAlta shareholders	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossAttributableToOwnersOfParent
36	Non-controlling interests (Note 12)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossAttributableToNoncontrollingInterests
37	Preferred share dividends (Note 25)	Concept (Monetary)	For Period	Debit	ifrs-full:DividendsPaid
38	Net earnings (loss) attributable to common shareholders	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossAttributableToOrdinaryEquityHoldersOfParentEntity
39	Weighted average number of common shares outstanding in the year (millions)	Concept (Shares)	For Period		ifrs-full:WeightedAverageShares
40	Net earnings (loss) per share attributable to common shareholders, basic and diluted (Note 24)	Concept (Share)	For Period		ifrs-full:BasicAndDilutedEarningsLossPerShare
41	1003000 - Statement - Consolidated Statements of Comprehensive Income (Loss) Statement	Network	*	*	http://www.transalta.com/role/ConsolidatedStatementsOfComprehensiveIncomeLossStatement
42	Implied Table	Table	*	*	implied:Table
43	Statement of comprehensive income [abstract]	Abstract			ifrs-full:StatementOfComprehensiveIncomeAbstract
44	Net earnings (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
45	Other comprehensive income (loss)	Abstract			ifrs-full:OtherComprehensiveIncomeAbstract
46	Net actuarial gains (losses) on defined benefit plans, net of tax	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeNetOfTaxGainsLossesOnRemeasurementsOfDefinedBenefitPlans
47	Gains (losses) on derivatives designated as cash flow hedges, net of tax	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeNetOfTaxCashFlowHedges
48	Total items that will not be reclassified subsequently to net earnings	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeThatWillNotBeReclassifiedToProfitOrLossNetOfTax
49	Gains (losses) on translating net assets of foreign operations,net of tax	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeNetOfTaxExchangeDifferencesOnTranslation
50	Reclassification of translation gains on net assets of divested foreign operations (Note 4)	Concept (Monetary)	For Period	Debit	ifrs-full:ReclassificationAdjustmentsOnExchangeDifferencesOnTranslationNetOfTax
51	Gains (losses) on financial instruments designated as hedges of foreign operations, net of tax	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnHedgesOfNetInvestmentsInForeignOperationsNetOfTax
52	Reclassification of losses on financial instruments designated as hedges of divested foreign operations, net of tax (Note 4)	Concept (Monetary)	For Period	Debit	ifrs-full:ReclassificationAdjustmentsOnHedgesOfNetInvestmentsInForeignOperationsNetOfTax
53	Gains (losses) on derivatives designated as cash flow hedges, net of tax	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnCashFlowHedgesNetOfTax
54	Reclassification of gains on derivatives designated as cash flow hedges to net earnings, net of tax	Concept (Monetary)	For Period	Debit	ifrs-full:ReclassificationAdjustmentsOnCashFlowHedgesNetOfTax
55	Total items that will be reclassified subsequently to net earnings	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeThatWillBeReclassifiedToProfitOrLossNetOfTax
56	Other comprehensive income	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncome
57	Total comprehensive income (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncome
58	Total comprehensive income (loss) attributable to:	Abstract			ifrs-full:ComprehensiveIncomeAttributableToAbstract
59	TransAlta shareholders	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncomeAttributableToOwnersOfParent
60	Non-controlling interests (Note 12)	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncomeAttributableToNoncontrollingInterests
61	Net actuarial gains (losses)	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxRelatingToRemeasurementsOfDefinedBenefitPlansOfOtherComprehensiveIncome
62	Income tax relating to gains (losses) on derivatives designated as cash flow hedges	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxRelatingToHedgesOfInvestmentsInEquityInstrumentsOfOtherComprehensiveIncome
63	Income tax relating to exchange differences on translation of other comprehensive income	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxRelatingToExchangeDifferencesOnTranslationOfOtherComprehensiveIncome
64	Income Tax Relating To Actuarial Gains (Losses) Arising From Changes In Financial Assumptions Of Other Comprehensive Income	Concept (Monetary)	For Period	Debit	tac:IncomeTaxRelatingToActuarialGainsLossesArisingFromChangesInFinancialAssumptionsOfOtherComprehensiveIncome
65	Income tax relating to hedges of net investments in foreign operations of other comprehensive income	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxRelatingToHedgesOfNetInvestmentsInForeignOperationsOfOtherComprehensiveIncome
66	Income tax recovery relating to reclassification Of Losses on financial instruments designed as hedges of divested foreign operations	Concept (Monetary)	For Period	Debit	tac:IncomeTaxExpenseRecoveryRelatingToReclassificationOfLossesOnFinancialInstrumentsDesignedAsHedgesOfDivestedForeignOperations
67	Income tax expense (recovery) relating to gains on derivatives designated as cash flow hedges of other comprehensive income	Concept (Monetary)	For Period	Debit	tac:IncomeTaxExpenseRecoveryRelatingToGainsOnDerivativesDesignatedAsCashFlowHedgesOfOtherComprehensiveIncome
68	Income tax expense relating to reclassification of gains on derivatives designated as cash flow hedges to net earnings	Concept (Monetary)	For Period	Debit	tac:IncomeTaxExpenseRecoveryRelatingToReclassificationOfGainsOnDerivativesDesignatedAsCashFlowHedgesToNetEarnings
69	1004000 - Statement - Consolidated Statements of Financial Position	Network	*	*	http://www.transalta.com/role/ConsolidatedStatementsOfFinancialPosition
70	Disclosure of detailed information about property, plant and equipment [table]	Table	*	*	ifrs-full:DisclosureOfPropertyPlantAndEquipmentTable
71	Classes of share capital [axis]	Axis			ifrs-full:ClassesOfShareCapitalAxis
72	Share capital [member]	Member			ifrs-full:ClassesOfShareCapitalMember
73	Common shares	Member			tac:CommonsharesMember
74	Preferred shares	Member			ifrs-full:PreferenceSharesMember
75	Carrying amount, accumulated depreciation, amortisation and impairment and gross carrying amount [axis]	Axis			ifrs-full:CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis
76	Carrying amount [member]	Member			ifrs-full:CarryingAmountMember
77	Gross carrying amount	Member			ifrs-full:GrossCarryingAmountMember
78	Accumulated depreciation	Member			ifrs-full:AccumulatedDepreciationAndAmortisationMember
79	Disclosure of detailed information about property, plant and equipment [line items]	LineItems			ifrs-full:DisclosureOfPropertyPlantAndEquipmentLineItems
80	Assets	Abstract			ifrs-full:AssetsAbstract
81	Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
82	Restricted cash (Note 22)	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentRestrictedCashAndCashEquivalents
83	Trade and other receivables (Note 13)	Concept (Monetary)	As Of	Debit	ifrs-full:TradeAndOtherCurrentReceivables
84	Risk management assets (Note 14 and 15)	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentDerivativeFinancialAssets
85	Inventory (Note 16)	Concept (Monetary)	As Of	Debit	ifrs-full:Inventories
86	Current assets	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentAssets
87	Restricted cash (Note 22)	Concept (Monetary)	As Of	Debit	ifrs-full:RestrictedCashAndCashEquivalents
88	Long-term portion of finance lease receivable (Note 8)	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentFinanceLeaseReceivables
89	Property, plant and equipment (Note 17)	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
90	Goodwill (Note 18)	Concept (Monetary)	As Of	Debit	ifrs-full:Goodwill
91	Intangible assets (Note 19)	Concept (Monetary)	As Of	Debit	ifrs-full:IntangibleAssetsOtherThanGoodwill
92	Deferred income tax assets (Note 11)	Concept (Monetary)	As Of	Debit	ifrs-full:DeferredTaxAssets
93	Risk management assets (Note 14 and 15)	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentDerivativeFinancialAssets
94	Other assets (Note 20)	Concept (Monetary)	As Of	Debit	ifrs-full:OtherNoncurrentAssets
95	Total assets	Concept (Monetary)	As Of	Debit	ifrs-full:Assets
96	Liabilities	Abstract			ifrs-full:LiabilitiesAbstract
97	Accounts payable and accrued liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:TradeAndOtherCurrentPayables
98	Current portion of decommissioning and other provisions (Note 21)	Concept (Monetary)	As Of	Credit	ifrs-full:ShorttermProvisionForDecommissioningRestorationAndRehabilitationCosts
99	Risk management liabilities (Note 14 and 15)	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentDerivativeFinancialLiabilities
100	Income taxes payable	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentTaxLiabilitiesCurrent
101	Dividends payable (Note 24 and 25)	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentDividendPayables
102	Current portion of long-term debt and finance lease obligations (Note 22)	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentBorrowingsAndCurrentPortionOfNoncurrentBorrowings
103	Current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentLiabilities
104	Credit facilities, long-term debt, and finance lease obligations (Note 22)	Concept (Monetary)	As Of	Credit	ifrs-full:LongtermBorrowings
105	Decommissioning and other provisions (Note 21)	Concept (Monetary)	As Of	Credit	ifrs-full:LongtermProvisionForDecommissioningRestorationAndRehabilitationCosts
106	Deferred income tax liabilities (Note 11)	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredTaxLiabilities
107	Risk management liabilities (Note 14 and 15)	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentDerivativeFinancialLiabilities
108	Contract liabilities (Note 5)	Concept (Monetary)	As Of	Credit	ifrs-full:ContractLiabilities
109	Defined benefit obligation and other long-term liabilities (Note 23)	Concept (Monetary)	As Of	Credit	tac:NoncurrentDefinedBenefitObligationAndOtherLongtermLiabilities
110	Equity	Abstract			ifrs-full:EquityAbstract
111	Issued capital (Note 24)	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
112	Contributed surplus	Concept (Monetary)	As Of	Credit	ifrs-full:AdditionalPaidinCapital
113	Deficit	Concept (Monetary)	As Of	Credit	ifrs-full:RetainedEarnings
114	Accumulated other comprehensive income (Note 26)	Concept (Monetary)	As Of	Credit	ifrs-full:AccumulatedOtherComprehensiveIncome
115	Equity attributable to shareholders	Concept (Monetary)	As Of	Credit	ifrs-full:EquityAttributableToOwnersOfParent
116	Non-controlling interests (Note 12)	Concept (Monetary)	As Of	Credit	ifrs-full:NoncontrollingInterests
117	Total equity	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
118	Total liabilities and equity	Concept (Monetary)	As Of	Credit	ifrs-full:EquityAndLiabilities
119	1005000 - Statement - Consolidated Statements of Changes in Equity	Network	*	*	http://www.transalta.com/role/ConsolidatedStatementsOfChangesInEquity
120	Statement of changes in equity [table]	Table	*	*	ifrs-full:StatementOfChangesInEquityTable
121	Classes of share capital [axis]	Axis			ifrs-full:ClassesOfShareCapitalAxis
122	Share capital [member]	Member			ifrs-full:ClassesOfShareCapitalMember
123	Common shares	Member			tac:CommonsharesMember
124	Preferred shares	Member			ifrs-full:PreferenceSharesMember
125	Components of equity [axis]	Axis			ifrs-full:ComponentsOfEquityAxis
126	Equity [member]	Member			ifrs-full:EquityMember
127	Common shares	Member			ifrs-full:IssuedCapitalMember
128	Preferred shares	Member			ifrs-full:PreferenceSharesMember
129	Contributed surplus	Member			ifrs-full:AdditionalPaidinCapitalMember
130	Deficit	Member			ifrs-full:RetainedEarningsMember
131	Other reserves [member]	Member			ifrs-full:OtherReservesMember
132	Accumulated other comprehensive income	Member			ifrs-full:AccumulatedOtherComprehensiveIncomeMember
133	Attributable to shareholders	Member			ifrs-full:EquityAttributableToOwnersOfParentMember
134	Attributable to non-controlling interests	Member			ifrs-full:NoncontrollingInterestsMember
135	Statement of changes in equity [line items]	LineItems			ifrs-full:StatementOfChangesInEquityLineItems
136	Balance, beginning of year	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
137	Net earnings (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
138	Other comprehensive income (loss)	Abstract			ifrs-full:OtherComprehensiveIncomeAbstract
139	Net losses on translating net assets of foreign operations, net of hedges and of tax	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnExchangeDifferencesOnTranslationNetOfTax
140	Net gains on derivatives designated as cash flow hedges, net of tax	Concept (Monetary)	For Period	Credit	tac:GainsLossesOnCashFlowHedgesRelatingToEquityNetOfTax
141	Net actuarial gains on defined benefits plans, net of tax	Concept (Monetary)	For Period	Debit	ifrs-full:ActuarialGainsLossesArisingFromChangesInDemographicAssumptionsNetDefinedBenefitLiabilityAsset
142	Intercompany available-for-sale investments	Concept (Monetary)	For Period	Credit	tac:IntercompanyAvailableForSaleInvestments
143	Intercompany fair value through other comprehensive income investments	Concept (Monetary)	For Period	Credit	tac:IntercompanyOtherComprehensiveIncomeInvestmentsFairValue
144	Total comprehensive income	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncome
145	Share dividends (Note 24)	Concept (Monetary)	For Period	Debit	ifrs-full:DividendsPaid
146	Changes in non-controlling interests in TransAlta Renewables (Note 4)	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughChangesInOwnershipInterestsInSubsidiariesThatDoNotResultInLossOfControl
147	Effect of share-based payment plans	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughSharebasedPaymentTransactions
148	Distributions paid, and payable, to non-controlling interests	Concept (Monetary)	For Period	Credit	ifrs-full:DividendsPaidToNoncontrollingInterests
149	Impact of change in accounting policy (Note 3)	Concept (Monetary)	As Of	Credit	tac:CumulativeEffectofNewAccountingPrincipleinPeriodofAdoption
150	Adjusted balance as at Jan. 1, 2018	Concept (Monetary)	As Of	Credit	tac:EquityAdjustedBalance
151	Shares purchased under NCIB	Concept (Monetary)	For Period	Credit	tac:StockIssuedDuringPeriodValueNewIssues1
152	Balance, end of year	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
153	1006000 - Statement - Consolidated Statement of Cash Flows	Network	*	*	http://www.transalta.com/role/ConsolidatedStatementOfCashFlows
154	Disclosure of classes of share capital [table]	Table	*	*	ifrs-full:DisclosureOfClassesOfShareCapitalTable
155	Classes of share capital [axis]	Axis			ifrs-full:ClassesOfShareCapitalAxis
156	Share capital [member]	Member			ifrs-full:ClassesOfShareCapitalMember
157	Common shares	Member			tac:CommonsharesMember
158	Preferred shares	Member			ifrs-full:PreferenceSharesMember
159	Disclosure of classes of share capital [line items]	LineItems			ifrs-full:DisclosureOfClassesOfShareCapitalLineItems
160	Operating activities	Abstract			ifrs-full:CashFlowsFromUsedInOperatingActivitiesAbstract
161	Net earnings (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
162	Depreciation and amortization (Note 34)	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDepreciationAndAmortisationExpense
163	Gain (loss) on sale of assets (Note 4)	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForLossesGainsOnDisposalOfNoncurrentAssets
164	Accretion of provisions (Note 21)	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForIncreaseInOtherProvisionsArisingFromPassageOfTime
165	Decommissioning and restoration costs settled (Note 21)	Concept (Monetary)	For Period	Debit	tac:AdjustmentsForDecommissioningAndRestorationCostsSettled
166	Deferred income tax expense (recovery) (Note 11)	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDeferredTaxExpense
167	Unrealized (gain) loss from risk management activities	Concept (Monetary)	For Period	Credit	ifrs-full:AdjustmentsForGainsLossesOnChangeInFairValueOfDerivatives
168	Unrealized foreign exchange (gain) loss	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForUnrealisedForeignExchangeLossesGains
169	Provisions	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForProvisions
170	Asset impairment charges (reversals) (Note 7)	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForImpairmentLossReversalOfImpairmentLossRecognisedInProfitOrLoss
171	Other non-cash items	Concept (Monetary)	For Period	Debit	ifrs-full:OtherAdjustmentsForNoncashItems
172	Cash flow from operations before changes in working capital	Concept (Monetary)	For Period		ifrs-full:CashFlowsFromUsedInOperationsBeforeChangesInWorkingCapital
173	Change in non-cash operating working capital balances (Note 30)	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseInWorkingCapital
174	Cash flow from operating activities	Concept (Monetary)	For Period		ifrs-full:CashFlowsFromUsedInOperatingActivities
175	Investing activities	Abstract			ifrs-full:CashFlowsFromUsedInInvestingActivitiesAbstract
176	Additions to property, plant and equipment (Note 17 and 34)	Concept (Monetary)	For Period	Credit	ifrs-full:PurchaseOfPropertyPlantAndEquipmentClassifiedAsInvestingActivities
177	Additions to intangibles (Note 19 and 34)	Concept (Monetary)	For Period	Credit	ifrs-full:PurchaseOfIntangibleAssetsClassifiedAsInvestingActivities
178	Restricted cash (Note 22)	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromUsedInDecreaseIncreaseInRestrictedCashAndCashEquivalents
179	Loan receivable (Note 20)	Concept (Monetary)	For Period	Credit	ifrs-full:CashAdvancesAndLoansMadeToOtherPartiesClassifiedAsInvestingActivities
180	Acquisition of renewable energy facilities, net of cash acquired (Note 4)	Concept (Monetary)	For Period	Credit	ifrs-full:CashFlowsUsedInObtainingControlOfSubsidiariesOrOtherBusinessesClassifiedAsInvestingActivities
181	Proceeds on sale of property, plant and equipment	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromSalesOfPropertyPlantAndEquipmentClassifiedAsInvestingActivities
182	Proceeds on sale of Wintering Hills facility and Solomon disposition (Note 4)	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromSalesOfInvestmentsAccountedForUsingEquityMethod
183	Income tax expense on Solomon disposition (Note 4 and 11)	Concept (Monetary)	For Period	Credit	ifrs-full:IncomeTaxesPaidRefundClassifiedAsInvestingActivities
184	Realized gains (losses) on financial instruments	Concept (Monetary)	For Period	Credit	tac:RealisedGainsLossesOnFinancialInstrumentClassifiedAsInvestingActivities
185	Decrease in finance lease receivable	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseInNetInvestmentInFinanceLease
186	Other	Concept (Monetary)	For Period	Debit	ifrs-full:OtherInflowsOutflowsOfCashClassifiedAsInvestingActivities
187	Change in non-cash investing working capital balances	Concept (Monetary)	For Period	Credit	tac:IncreaseDecreaseInInvestingWorkingCapital
188	Cash flow from (used in) investing activities	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromUsedInInvestingActivities
189	Financing activities	Abstract			ifrs-full:CashFlowsFromUsedInFinancingActivitiesAbstract
190	Net increase (decrease) in borrowings under credit facilities (Note 22)	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromUsedInIncreaseDecreaseInCurrentBorrowings
191	Repayment of long-term debt (Note 22)	Concept (Monetary)	For Period	Credit	ifrs-full:RepaymentsOfBorrowingsClassifiedAsFinancingActivities
192	Issuance of long-term debt (Note 22)	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromCurrentBorrowings
193	Dividends paid, classified as financing activities	Concept (Monetary)	For Period	Credit	ifrs-full:DividendsPaidClassifiedAsFinancingActivities
194	Net proceeds on sale of non-controlling interest in subsidiary (Note 4)	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromChangesInOwnershipInterestsInSubsidiaries
195	Repurchase of common shares under NCIB (Note 24)	Concept (Monetary)	For Period	Credit	ifrs-full:PaymentsToAcquireOrRedeemEntitysShares
196	Realized gains (losses) on financial instruments	Concept (Monetary)	For Period	Credit	tac:RealisedGainsLossesOnFinancialInstrumentClassifiedAsFinancingActivities
197	Distributions paid to subsidiaries' non-controlling interests (Note 12)	Concept (Monetary)	For Period	Credit	ifrs-full:DividendsPaidToNoncontrollingInterestsClassifiedAsFinancingActivities
198	Decrease in finance lease obligations (Note 22)	Concept (Monetary)	For Period	Credit	tac:IncreaseDecreaseInFinanceLeaseObligation
199	Other	Concept (Monetary)	For Period	Debit	ifrs-full:OtherInflowsOutflowsOfCashClassifiedAsFinancingActivities
200	Change in non-cash financing working capital balances	Concept (Monetary)	For Period	Credit	tac:IncreaseDecreaseInNonCashFinancingWorkingCapital
201	Cash flow from (used in) financing activities	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromUsedInFinancingActivities
202	Cash flow from (used in) operating, investing, and financing activities	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseInCashAndCashEquivalentsBeforeEffectOfExchangeRateChanges
203	Effect of translation on foreign currency cash	Concept (Monetary)	For Period	Debit	ifrs-full:EffectOfExchangeRateChangesOnCashAndCashEquivalents
204	Increase (decrease) in cash and cash equivalents	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseInCashAndCashEquivalents
205	Cash and cash equivalents, beginning of year	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
206	Cash and cash equivalents, end of year	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
207	Cash income taxes paid	Concept (Monetary)	For Period	Credit	ifrs-full:IncomeTaxesPaidRefund
208	Cash interest paid	Concept (Monetary)	For Period	Credit	ifrs-full:InterestPaidClassifiedAsOperatingActivities
209	2101100 - Disclosure - Corporate Information (Notes)	Network	*	*	http://www.transalta.com/role/CorporateInformationNotes
210	Implied Table	Table	*	*	implied:Table
211	Corporate Information and Statement of IFRS Compliance [Abstract]	Abstract			tac:CorporateInformationandStatementofIFRSComplianceAbstract
212	Corporate Information	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfNotesAndOtherExplanatoryInformationExplanatory
213	2104100 - Disclosure - Significant Accounting Policies	Network	*	*	http://www.transalta.com/role/SignificantAccountingPolicies
214	Implied Table	Table	*	*	implied:Table
215	Disclosure of changes in accounting policies, accounting estimates and errors [Abstract]	Abstract			tac:DisclosureofchangesinaccountingpoliciesaccountingestimatesanderrorsAbstract
216	Significant Accounting Policies	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfSummaryOfSignificantAccountingPoliciesExplanatory
217	2107100 - Disclosure - Accounting Changes	Network	*	*	http://www.transalta.com/role/AccountingChanges
218	Implied Table	Table	*	*	implied:Table
219	Disclosure of changes in accounting policies, accounting estimates and errors [Abstract]	Abstract			tac:DisclosureofchangesinaccountingpoliciesaccountingestimatesanderrorsAbstract
220	Accounting Changes	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfChangesInAccountingPoliciesExplanatory
221	21100100 - Disclosure - Significant Events	Network	*	*	http://www.transalta.com/role/SignificantEvents
222	Implied Table	Table	*	*	implied:Table
223	Significant Events [Abstract]	Abstract			tac:SignificantEventsAbstract
224	Significant Events	Concept (Text Block (HTML))	For Period		tac:DisclosureOfSignificantEventsTextBlock
225	2110100 - Disclosure - Revenue	Network	*	*	http://www.transalta.com/role/Revenue
226	Implied Table	Table	*	*	implied:Table
227	Disclosure of revenue from contracts with customers [Abstract]	Abstract			tac:DisclosureofrevenuefromcontractswithcustomersAbstract
228	Revenue	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfRevenueFromContractsWithCustomersExplanatory
229	2113100 - Disclosure - Expenses by Nature	Network	*	*	http://www.transalta.com/role/ExpensesByNature
230	Implied Table	Table	*	*	implied:Table
231	Analysis of income and expense [abstract]	Abstract			ifrs-full:AnalysisOfIncomeAndExpenseAbstract
232	Expenses by Nature	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfExpensesByNatureExplanatory
233	2115100 - Disclosure - Asset Impairment Charges and Reversals	Network	*	*	http://www.transalta.com/role/AssetImpairmentChargesAndReversals
234	Implied Table	Table	*	*	implied:Table
235	Disclosure of impairment of assets [Abstract]	Abstract			tac:DisclosureofimpairmentofassetsAbstract
236	Asset Impairment Charges and Reversals	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfImpairmentOfAssetsExplanatory
237	2116100 - Disclosure - Finance Lease Receivables	Network	*	*	http://www.transalta.com/role/FinanceLeaseReceivables
238	Implied Table	Table	*	*	implied:Table
239	Disclosure of leases [Abstract]	Abstract			tac:DisclosureofleasesAbstract
240	Finance Lease Receivables	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfLeasesExplanatory
241	2119100 - Disclosure - Net Other Operating (Income) Losses	Network	*	*	http://www.transalta.com/role/NetOtherOperatingIncomeLosses
242	Implied Table	Table	*	*	implied:Table
243	Analysis of income and expense [abstract]	Abstract			ifrs-full:AnalysisOfIncomeAndExpenseAbstract
244	Net other operating (income) losses	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfOtherOperatingIncomeExpenseExplanatory
245	2120100 - Disclosure - Net Interest Expense	Network	*	*	http://www.transalta.com/role/NetInterestExpense
246	Implied Table	Table	*	*	implied:Table
247	Net Interest Expense [Abstract]	Abstract			tac:NetInterestExpenseAbstract
248	Net interest expense	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInterestExpenseExplanatory
249	2122100 - Disclosure - Income Taxes	Network	*	*	http://www.transalta.com/role/IncomeTaxes
250	Implied Table	Table	*	*	implied:Table
251	Income Taxes [Abstract]	Abstract			tac:IncomeTaxesAbstract
252	Income Taxes	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfIncomeTaxExplanatory
253	2125100 - Disclosure - Non-Controlling Interests	Network	*	*	http://www.transalta.com/role/NonControllingInterests
254	Implied Table	Table	*	*	implied:Table
255	Interests In Other Entities [Abstract]	Abstract			tac:InterestsInOtherEntitiesAbstract
256	Non-Controlling Interests	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfNoncontrollingInterestsExplanatory
257	2128100 - Disclosure - Trade and Other Receivables	Network	*	*	http://www.transalta.com/role/TradeAndOtherReceivables
258	Implied Table	Table	*	*	implied:Table
259	Subclassifications of assets, liabilities and equities [abstract]	Abstract			ifrs-full:SubclassificationsOfAssetsLiabilitiesAndEquitiesAbstract
260	Trade and Other Receivables	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfTradeAndOtherReceivablesExplanatory
261	2131100 - Disclosure - Financial Instruments	Network	*	*	http://www.transalta.com/role/FinancialInstruments
262	Implied Table	Table	*	*	implied:Table
263	Disclosure of detailed information about financial instruments [abstract]	Abstract			ifrs-full:DisclosureOfFinancialInstrumentsAbstract
264	Financial Instruments	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinancialInstrumentsExplanatory
265	2137100 - Disclosure - Risk Management Activities	Network	*	*	http://www.transalta.com/role/RiskManagementActivities
266	Implied Table	Table	*	*	implied:Table
267	Financial Instruments [Abstract]	Abstract			tac:FinancialInstrumentsAbstract
268	Risk Management Activities	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinancialRiskManagementExplanatory
269	2140100 - Disclosure - Inventory (Notes)	Network	*	*	http://www.transalta.com/role/InventoryNotes
270	Implied Table	Table	*	*	implied:Table
271	Disclosure of inventories [Abstract]	Abstract			tac:DisclosureofinventoriesAbstract
272	Inventory	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInventoriesExplanatory
273	2143100 - Disclosure - Property, Plant, and Equipment (Notes)	Network	*	*	http://www.transalta.com/role/PropertyPlantAndEquipmentNotes
274	Implied Table	Table	*	*	implied:Table
275	Disclosure of detailed information about property, plant and equipment [abstract]	Abstract			ifrs-full:DisclosureOfPropertyPlantAndEquipmentAbstract
276	Property, Plant, and Equipment	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfPropertyPlantAndEquipmentExplanatory
277	2149100 - Disclosure - Goodwill (Notes)	Network	*	*	http://www.transalta.com/role/GoodwillNotes
278	Implied Table	Table	*	*	implied:Table
279	Disclosure of detailed information about goodwill [Abstract]	Abstract			tac:DisclosureofdetailedinformationaboutgoodwillAbstract
280	Goodwill	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfGoodwillExplanatory
281	2158100 - Disclosure - Intangible Assets (Notes)	Network	*	*	http://www.transalta.com/role/IntangibleAssetsNotes
282	Implied Table	Table	*	*	implied:Table
283	Disclosure of detailed information about intangible assets [abstract]	Abstract			ifrs-full:DisclosureOfIntangibleAssetsAbstract
284	Intangible Assets	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfIntangibleAssetsExplanatory
285	2161100 - Disclosure - Other Assets (Notes)	Network	*	*	http://www.transalta.com/role/OtherAssetsNotes
286	Implied Table	Table	*	*	implied:Table
287	Disclosure of financial assets [abstract]	Abstract			ifrs-full:DisclosureOfFinancialAssetsAbstract
288	Other Assets	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfOtherNoncurrentAssetsExplanatory
289	2164100 - Disclosure - Decommissioning and Other Provisions	Network	*	*	http://www.transalta.com/role/DecommissioningAndOtherProvisions
290	Implied Table	Table	*	*	implied:Table
291	Other Provisions, Contingent Liabilities And Contingent Assets [Abstract]	Abstract			tac:OtherProvisionsContingentLiabilitiesAndContingentAssetsAbstract
292	Decommissioning and Other Provisions	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfProvisionsExplanatory
293	2167100 - Disclosure - Credit Facilities, Long-Term Debt, and Finance Lease Obligations	Network	*	*	http://www.transalta.com/role/CreditFacilitiesLongTermDebtAndFinanceLeaseObligations
294	Implied Table	Table	*	*	implied:Table
295	Subclassifications of assets, liabilities and equities [abstract]	Abstract			ifrs-full:SubclassificationsOfAssetsLiabilitiesAndEquitiesAbstract
296	Credit Facilities, Long-Term Debt, and Finance Lease Obligations	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfBorrowingsExplanatory
297	2170100 - Disclosure - Defined Benefit Obligation and Other Long-Term Liabilities	Network	*	*	http://www.transalta.com/role/DefinedBenefitObligationAndOtherLongTermLiabilities
298	Implied Table	Table	*	*	implied:Table
299	Subclassifications of assets, liabilities and equities [abstract]	Abstract			ifrs-full:SubclassificationsOfAssetsLiabilitiesAndEquitiesAbstract
300	Defined Benefit Obligation and Other Long-Term Liabilities	Concept (Text Block (HTML))	For Period		tac:DisclosureOfNoncurrentDefinedBenefitPlanLiabilitiesandOtherNoncurrentLiabilitiesTextBlock
301	2173100 - Disclosure - Common Shares	Network	*	*	http://www.transalta.com/role/CommonShares
302	Implied Table	Table	*	*	implied:Table
303	Share Capital, Reserves And Other Equity Interest [Abstract]	Abstract			tac:ShareCapitalReservesAndOtherEquityInterestAbstract
304	Common Shares	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfShareCapitalReservesAndOtherEquityInterestExplanatory
305	2176100 - Disclosure - Preferred Shares	Network	*	*	http://www.transalta.com/role/PreferredShares
306	Implied Table	Table	*	*	implied:Table
307	Share Capital, Reserves And Other Equity Interest [Abstract]	Abstract			tac:ShareCapitalReservesAndOtherEquityInterestAbstract
308	Preferred Shares	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfShareCapitalReservesAndOtherEquityInterestExplanatory
309	2179100 - Disclosure - Accumulated Other Comprehensive Income	Network	*	*	http://www.transalta.com/role/AccumulatedOtherComprehensiveIncome
310	Implied Table	Table	*	*	implied:Table
311	Disclosure of analysis of other comprehensive income by item [abstract]	Abstract			ifrs-full:DisclosureOfAnalysisOfOtherComprehensiveIncomeByItemAbstract
312	Accumulated other comprehensive income	Concept (Text Block (HTML))	For Period		tac:DisclosureOfAccumulatedOtherComprehensiveIncomeTextBlock
313	2182100 - Disclosure - Share-Based Payment Plans	Network	*	*	http://www.transalta.com/role/ShareBasedPaymentPlans
314	Implied Table	Table	*	*	implied:Table
315	Share-based payment arrangements [Abstract]	Abstract			tac:SharebasedpaymentarrangementsAbstract
316	Share-Based Payment Plans	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfSharebasedPaymentArrangementsExplanatory
317	2185100 - Disclosure - Employee Future Benefits	Network	*	*	http://www.transalta.com/role/EmployeeFutureBenefits
318	Implied Table	Table	*	*	implied:Table
319	Employee Benefits [Abstract]	Abstract			tac:EmployeeBenefitsAbstract
320	Employee Future Benefits	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfEmployeeBenefitsExplanatory
321	2188100 - Disclosure - Joint Arrangements	Network	*	*	http://www.transalta.com/role/JointArrangements
322	Implied Table	Table	*	*	implied:Table
323	Disclosure of interests in other entities [Abstract]	Abstract			tac:DisclosureofinterestsinotherentitiesAbstract
324	Joint arrangements	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInterestsInOtherEntitiesExplanatory
325	2191100 - Disclosure - Cash Flow Information (Notes)	Network	*	*	http://www.transalta.com/role/CashFlowInformationNotes
326	Implied Table	Table	*	*	implied:Table
327	Disclosure of cash flow statement [Abstract]	Abstract			tac:DisclosureofcashflowstatementAbstract
328	Cash Flow Information	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesExplanatory
329	2194100 - Disclosure - Capital	Network	*	*	http://www.transalta.com/role/Capital
330	Implied Table	Table	*	*	implied:Table
331	Disclosure of notes and other explanatory information [Abstract]	Abstract			tac:DisclosureofnotesandotherexplanatoryinformationAbstract
332	Capital	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfObjectivesPoliciesAndProcessesForManagingCapitalExplanatory
333	2197100 - Disclosure - Related Party Transactions	Network	*	*	http://www.transalta.com/role/RelatedPartyTransactions
334	Implied Table	Table	*	*	implied:Table
335	Related Party [Abstract]	Abstract			tac:RelatedPartyAbstract
336	Related Party Transactions	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfRelatedPartyExplanatory
337	2198100 - Disclosure - Commitments and Contingencies	Network	*	*	http://www.transalta.com/role/CommitmentsAndContingencies
338	Implied Table	Table	*	*	implied:Table
339	Disclosure of other provisions, contingent liabilities and contingent assets [Abstract]	Abstract			tac:DisclosureofotherprovisionscontingentliabilitiesandcontingentassetsAbstract
340	Commitments and Contingencies	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfCommitmentsAndContingentLiabilitiesExplanatory
341	2198100 - Disclosure - Segment Disclosures (Notes)	Network	*	*	http://www.transalta.com/role/SegmentDisclosuresNotes
342	Implied Table	Table	*	*	implied:Table
343	Disclosure of entity's operating segments [Abstract]	Abstract			tac:DisclosureofentitysoperatingsegmentsAbstract
344	Segments Disclosures	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfEntitysReportableSegmentsExplanatory
345	2204201 - Disclosure - Significant Accounting Policies (Policies)	Network	*	*	http://www.transalta.com/role/SignificantAccountingPoliciesPolicies
346	Implied Table	Table	*	*	implied:Table
347	Disclosure of changes in accounting policies, accounting estimates and errors [Abstract]	Abstract			tac:DisclosureofchangesinaccountingpoliciesaccountingestimatesanderrorsAbstract
348	Revenue recognition	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForRecognitionOfRevenue
349	Foreign currency translation	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForForeignCurrencyTranslationExplanatory
350	Financial instruments and hedges	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForFinancialInstrumentsExplanatory
351	Cash and cash equivalents	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyToDetermineComponentsOfCashAndCashEquivalents
352	Collateral paid and received	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForCollateralExplanatory
353	Inventory	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForMeasuringInventories
354	Property, plant and equipment	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForPropertyPlantAndEquipmentExplanatory
355	Intangible assets	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForIntangibleAssetsOtherThanGoodwillExplanatory
356	Impairment of tangible and intangible assets excluding goodwill	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForImpairmentOfAssetsExplanatory
357	Goodwill	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForGoodwillExplanatory
358	Project development costs	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForResearchAndDevelopmentExpenseExplanatory
359	Income taxes	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForIncomeTaxExplanatory
360	Employee future benefits	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForEmployeeBenefitsExplanatory
361	Provisions	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForProvisionsExplanatory
362	Share-based payments	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForSharebasedPaymentTransactionsExplanatory
363	Emission Credits and Allowances	Concept (Text Block (HTML))	For Period		tac:EmissionCreditsandAllowancesPolicyTextBlock
364	Assets Held for Sale	Concept (Text Block (HTML))	For Period		tac:AssetsHeldForSalePolicyTextBlock
365	Leases	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForLeasesExplanatory
366	Borrowing costs	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForBorrowingCostsExplanatory
367	Non-controlling interests	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForTransactionsWithNoncontrollingInterestsExplanatory
368	Joint arrangements	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForInvestmentInAssociatesAndJointVenturesExplanatory
369	Government incentives	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForGovernmentGrants
370	Earnings per share	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForEarningsPerShareExplanatory
371	Business combinations	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForBusinessCombinationsExplanatory
372	Stripping costs	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForStrippingCostsExplanatory
373	Significant accounting judgments and key sources of estimation uncertainty	Concept (Text Block (HTML))	For Period		tac:DescriptionOfAccountingPolicyForSignificantAccountingJudgmentsAndKeySourcesOfEstimationUncertaintyPolicyTextBlock
374	2304302 - Disclosure - Significant Accounting Policies (Tables)	Network	*	*	http://www.transalta.com/role/SignificantAccountingPoliciesTables
375	Implied Table	Table	*	*	implied:Table
376	Disclosure of changes in accounting policies, accounting estimates and errors [Abstract]	Abstract			tac:DisclosureofchangesinaccountingpoliciesaccountingestimatesanderrorsAbstract
377	Disclosure of detailed information about property, plant and equipment	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDetailedInformationAboutPropertyPlantAndEquipmentExplanatory
378	Disclosure of detailed information about intangible assets	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDetailedInformationAboutIntangibleAssetsExplanatory
379	2307301 - Disclosure - Accounting Changes - (Tables)	Network	*	*	http://www.transalta.com/role/AccountingChangesTables
380	Implied Table	Table	*	*	implied:Table
381	Disclosure of changes in accounting policies, accounting estimates and errors [Abstract]	Abstract			tac:DisclosureofchangesinaccountingpoliciesaccountingestimatesanderrorsAbstract
382	Disclosure Of Comparative Information Prepared Under Previous GAAP [Table Text Block]	Concept (Text Block (HTML))	For Period		tac:DisclosureOfComparativeInformationPreparedUnderPreviousGAAPTableTextBlock
383	2310301 - Disclosure - Revenue (Tables)	Network	*	*	http://www.transalta.com/role/RevenueTables
384	Implied Table	Table	*	*	implied:Table
385	Disclosure of revenue from contracts with customers [Abstract]	Abstract			tac:DisclosureofrevenuefromcontractswithcustomersAbstract
386	Disaggregation Of Revenue	Concept (Text Block (HTML))	For Period		tac:DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersTableTextBlock
387	Changes In Contract Liabilities	Concept (Text Block (HTML))	For Period		tac:ChangesInContractWithCustomerLiabilityTableTextBlock
388	2313301 - Disclosure - Expenses by Nature (Tables)	Network	*	*	http://www.transalta.com/role/ExpensesByNatureTables
389	Implied Table	Table	*	*	implied:Table
390	Analysis of income and expense [abstract]	Abstract			ifrs-full:AnalysisOfIncomeAndExpenseAbstract
391	Expenses classified by nature	Concept (Text Block (HTML))	For Period		tac:DisclosureOfExpensesClassifiedByNatureTableTextBlock
392	2316301 - Disclosure - Finance Lease Receivables (Tables)	Network	*	*	http://www.transalta.com/role/FinanceLeaseReceivablesTables
393	Implied Table	Table	*	*	implied:Table
394	Disclosure of leases [Abstract]	Abstract			tac:DisclosureofleasesAbstract
395	Disclosure of recognised finance lease	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinanceLeaseAndOperatingLeaseByLessorExplanatory
396	2319301 - Disclosure - Net Other Operating (Income) Losses (Tables)	Network	*	*	http://www.transalta.com/role/NetOtherOperatingIncomeLossesTables
397	Implied Table	Table	*	*	implied:Table
398	Analysis of income and expense [abstract]	Abstract			ifrs-full:AnalysisOfIncomeAndExpenseAbstract
399	Disclosure of components of net other operating (income) losses	Concept (Text Block (HTML))	For Period		tac:DisclosureofcomponentsofnetotheroperatingincomelossesTableTextBlock
400	2320301 - Disclosure - Net Interest Expense (Tables)	Network	*	*	http://www.transalta.com/role/NetInterestExpenseTables
401	Implied Table	Table	*	*	implied:Table
402	Analysis of income and expense [abstract]	Abstract			ifrs-full:AnalysisOfIncomeAndExpenseAbstract
403	Components of net interest expense	Concept (Text Block (HTML))	For Period		tac:DisclosureofcomponentsofinterestexpenseTableTextBlock
404	2322301 - Disclosure - Income Taxes (Tables)	Network	*	*	http://www.transalta.com/role/IncomeTaxesTables
405	Implied Table	Table	*	*	implied:Table
406	Income Taxes [Abstract]	Abstract			tac:IncomeTaxesAbstract
407	Rate reconciliations	Concept (Text Block (HTML))	For Period		tac:DisclosureOfReconciliationOfAccountingProfitMultipliedByApplicableTaxRatesAndAverageEffectiveTaxRateTableTextBlock
408	Components of income tax expense	Concept (Text Block (HTML))	For Period		tac:DisclosureOfMajorComponentsOfTaxExpenseIncomeTableTextBlock
409	Aggregate current and deferred income tax related to items charged or credited to equity	Concept (Text Block (HTML))	For Period		tac:DisclosureOfCurrentAndDeferredIncomeTaxItemsChargedToEquityTableTextBlock
410	Disclosure of temporary difference, unused tax losses and unused tax credits [text block]	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsExplanatory
411	2325301 - Disclosure - Non-Controlling Interests (Tables)	Network	*	*	http://www.transalta.com/role/NonControllingInterestsTables
412	Implied Table	Table	*	*	implied:Table
413	Interests In Other Entities [Abstract]	Abstract			tac:InterestsInOtherEntitiesAbstract
414	Share of ownership and equity participation in TransAlta Renewables	Concept (Text Block (HTML))	For Period		tac:DisclosureOfNoncontrollingInterestsTableTextBlock
415	Subsidiaries and operations with non-controlling interests	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfEffectsOfChangesInParentsOwnershipInterestInSubsidiaryThatDoNotResultInLossOfControlOnEquityAttributableToOwnersOfParentExplanatory
416	Disclosure of interests in subsidiaries	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInterestsInSubsidiariesExplanatory
417	2328301 - Disclosure - Trade and Other Receivables (Tables)	Network	*	*	http://www.transalta.com/role/TradeAndOtherReceivablesTables
418	Implied Table	Table	*	*	implied:Table
419	Subclassifications of assets, liabilities and equities [abstract]	Abstract			ifrs-full:SubclassificationsOfAssetsLiabilitiesAndEquitiesAbstract
420	Trade and Other Receivables	Concept (Text Block (HTML))	For Period		tac:ComponentsofTradeandOtherReceivablesTableTextBlock
421	2331301 - Disclosure - Financial Instruments (Tables)	Network	*	*	http://www.transalta.com/role/FinancialInstrumentsTables
422	Implied Table	Table	*	*	implied:Table
423	Disclosure of detailed information about financial instruments [abstract]	Abstract			ifrs-full:DisclosureOfFinancialInstrumentsAbstract
424	Disclosure of financial assets	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinancialAssetsExplanatory
425	Disclosure of financial liabilities	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinancialLiabilitiesExplanatory
426	Disclosure for sensitivity ranges for the base fair value	Concept (Text Block (HTML))	For Period		tac:DisclosureForSensitivityRangesForTheBaseFairValueTableTextBlock
427	Disclosure of risk management strategy related to hedge accounting	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfRiskManagementStrategyRelatedToHedgeAccountingExplanatory
428	Disclosure of fair value measurement of liabilities	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFairValueMeasurementOfLiabilitiesExplanatory
429	Disclosure of difference between transaction price and the fair value determined using valuation model	Concept (Text Block (HTML))	For Period		tac:DisclosureOfDifferenceBetweenTransactionPriceAndTheFairValueDeterminedUsingValuationModelTableTextBlock
430	2337301 - Disclosure - Risk Management Activities (Tables)	Network	*	*	http://www.transalta.com/role/RiskManagementActivitiesTables
431	Implied Table	Table	*	*	implied:Table
432	Financial Instruments [Abstract]	Abstract			tac:FinancialInstrumentsAbstract
433	Derivative Financial Instruments	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDerivativeFinancialInstrumentsExplanatory
434	Net Arrangements	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfOffsettingOfFinancialAssetsAndFinancialLiabilitiesExplanatory
435	Effect of Hedges	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDetailedInformationAboutHedgedItemsExplanatory
436	Interest Rate Risk	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsExplanatory
437	Currency Rate Risk	Concept (Text Block (HTML))	For Period		ifrs-full:SensitivityAnalysisForEachTypeOfMarketRisk
438	Credit Risk	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfCreditRiskExplanatory
439	Maturity Analysis of Financial Liabilities	Concept (Text Block (HTML))	For Period		ifrs-full:MaturityAnalysisForDerivativeFinancialLiabilities
440	Hedging Instruments	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDetailedInformationAboutHedgingInstrumentsExplanatory
441	2340301 - Disclosure - Inventory (Tables)	Network	*	*	http://www.transalta.com/role/InventoryTables
442	Implied Table	Table	*	*	implied:Table
443	Disclosure of inventories [Abstract]	Abstract			tac:DisclosureofinventoriesAbstract
444	Disclosure Of The Components Of Inventories	Concept (Text Block (HTML))	For Period		tac:DisclosureOfTheComponentsOfInventoriesTableTextBlock
445	Disclosure Of The Change In Inventory	Concept (Text Block (HTML))	For Period		tac:DisclosureOfTheChangeInInventoryTableTextBlock
446	2343301 - Disclosure - Property, Plant, and Equipment (Tables)	Network	*	*	http://www.transalta.com/role/PropertyPlantAndEquipmentTables
447	Implied Table	Table	*	*	implied:Table
448	Disclosure of detailed information about property, plant and equipment [abstract]	Abstract			ifrs-full:DisclosureOfPropertyPlantAndEquipmentAbstract
449	Disclosure of detailed information about property, plant and equipment	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDetailedInformationAboutPropertyPlantAndEquipmentExplanatory
450	2349301 - Disclosure - Goodwill (Tables)	Network	*	*	http://www.transalta.com/role/GoodwillTables
451	Implied Table	Table	*	*	implied:Table
452	Disclosure of detailed information about goodwill [Abstract]	Abstract			tac:DisclosureofdetailedinformationaboutgoodwillAbstract
453	Disclosure of detailed information about goodwill	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfReconciliationOfChangesInIntangibleAssetsAndGoodwillExplanatory
454	2358301 - Disclosure - Intangible Assets (Tables)	Network	*	*	http://www.transalta.com/role/IntangibleAssetsTables
455	Implied Table	Table	*	*	implied:Table
456	Disclosure of detailed information about intangible assets [abstract]	Abstract			ifrs-full:DisclosureOfIntangibleAssetsAbstract
457	Disclosure of reconciliation of changes in intangible assets	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfReconciliationOfChangesInIntangibleAssetsAndGoodwillExplanatory
458	2361301 - Disclosure - Other Assets (Tables)	Network	*	*	http://www.transalta.com/role/OtherAssetsTables
459	Implied Table	Table	*	*	implied:Table
460	Disclosure of financial assets [abstract]	Abstract			ifrs-full:DisclosureOfFinancialAssetsAbstract
461	Disclosure of components in other assets	Concept (Text Block (HTML))	For Period		tac:DisclosureofComponentsinOtherAssetsTableTextBlock
462	2364301 - Disclosure - Decommissioning and Other Provisions (Tables)	Network	*	*	http://www.transalta.com/role/DecommissioningAndOtherProvisionsTables
463	Implied Table	Table	*	*	implied:Table
464	Other Provisions, Contingent Liabilities And Contingent Assets [Abstract]	Abstract			tac:OtherProvisionsContingentLiabilitiesAndContingentAssetsAbstract
465	Change in decommissioning and other provision balances	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfOtherProvisionsExplanatory
466	2367301 - Disclosure - Credit Facilities, Long-Term Debt, and Finance Lease Obligations (Tables)	Network	*	*	http://www.transalta.com/role/CreditFacilitiesLongTermDebtAndFinanceLeaseObligationsTables
467	Implied Table	Table	*	*	implied:Table
468	Subclassifications of assets, liabilities and equities [abstract]	Abstract			ifrs-full:SubclassificationsOfAssetsLiabilitiesAndEquitiesAbstract
469	Disclosure of borrowings outstanding	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsExplanatory
470	Disclosure of principal repayments	Concept (Text Block (HTML))	For Period		tac:DisclosureOfPrincipalRepaymentsTableTextBlock
471	Disclosure of amounts payable for mining assets and other finance leases	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfRecognisedFinanceLeaseAsAssetsByLesseeExplanatory
472	2370301 - Disclosure - Defined Benefit Obligation and Other Long-Term Liabilities (Tables)	Network	*	*	http://www.transalta.com/role/DefinedBenefitObligationAndOtherLongTermLiabilitiesTables
473	Implied Table	Table	*	*	implied:Table
474	Subclassifications of assets, liabilities and equities [abstract]	Abstract			ifrs-full:SubclassificationsOfAssetsLiabilitiesAndEquitiesAbstract
475	Components of Defined Benefit Obligations and Other Long-Term Liabilities	Concept (Text Block (HTML))	For Period		tac:ComponentsofNoncurrentDefinedBenefitPlanLiabilitiesandOtherLongTermLiabilitiesTableTextBlock
476	2373301 - Disclosure - Common Shares (Tables)	Network	*	*	http://www.transalta.com/role/CommonSharesTables
477	Implied Table	Table	*	*	implied:Table
478	Share Capital, Reserves And Other Equity Interest [Abstract]	Abstract			tac:ShareCapitalReservesAndOtherEquityInterestAbstract
479	Issued and outstanding	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfClassesOfShareCapitalExplanatory
480	Earnings per share	Concept (Text Block (HTML))	For Period		ifrs-full:EarningsPerShareExplanatory
481	2376301 - Disclosure - Preferred Shares (Tables)	Network	*	*	http://www.transalta.com/role/PreferredSharesTables
482	Implied Table	Table	*	*	implied:Table
483	Share Capital, Reserves And Other Equity Interest [Abstract]	Abstract			tac:ShareCapitalReservesAndOtherEquityInterestAbstract
484	Issued and outstanding	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfClassesOfShareCapitalExplanatory
485	Characteristics specific to preferred share series	Concept (Text Block (HTML))	For Period		tac:DisclosureOfCharacteristicsOfPreferenceSharesTableTextBlock
486	Disclosure Of Dividends Declared On Preference Shares [Table Text Block]	Concept (Text Block (HTML))	For Period		tac:DisclosureOfDividendsDeclaredOnPreferenceSharesTableTextBlock
487	2379301 - Disclosure - Accumulated Other Comprehensive Income (Tables)	Network	*	*	http://www.transalta.com/role/AccumulatedOtherComprehensiveIncomeTables
488	Implied Table	Table	*	*	implied:Table
489	Disclosure of analysis of other comprehensive income by item [abstract]	Abstract			ifrs-full:DisclosureOfAnalysisOfOtherComprehensiveIncomeByItemAbstract
490	Disclosure of changes in accumulated other comprehensive income (loss)	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfAnalysisOfOtherComprehensiveIncomeByItemExplanatory
491	2382301 - Disclosure - Share-Based Payment Plans (Tables)	Network	*	*	http://www.transalta.com/role/ShareBasedPaymentPlansTables
492	Implied Table	Table	*	*	implied:Table
493	Share-based payment arrangements [Abstract]	Abstract			tac:SharebasedpaymentarrangementsAbstract
494	Disclosure of range of exercise prices of outstanding share options	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsExplanatory
495	Disclosure of number and weighted average remaining contractual life of outstanding share options	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfNumberAndWeightedAverageRemainingContractualLifeOfOutstandingShareOptionsExplanatory
496	2385301 - Disclosure - Employee Future Benefits (Tables)	Network	*	*	http://www.transalta.com/role/EmployeeFutureBenefitsTables
497	Implied Table	Table	*	*	implied:Table
498	Employee Benefits [Abstract]	Abstract			tac:EmployeeBenefitsAbstract
499	Costs Recognized	Concept (Text Block (HTML))	For Period		tac:DisclosureOfDefinedBenefitPlanExpenseRecognizedInProfitOrLossExplanatoryTableTextBlock
500	Defined Benefit Obligation	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfNetDefinedBenefitLiabilityAssetExplanatory
501	Plan Assets	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFairValueOfPlanAssetsExplanatory
502	Assumptions	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDefinedBenefitPlansExplanatory
503	Schedule of Estimated Increase In The Net Defined Benefit Obligation Assuming Certain Changes In Key Assumptions	Concept (Text Block (HTML))	For Period		tac:EstimatedIncreaseInTheNetDefinedBenefitObligationAssumingCertainChangesInKeyAssumptionsTableTextBlock
504	Sensitivity Analysis	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfSensitivityAnalysisForActuarialAssumptionsExplanatory
505	2388301 - Disclosure - Joint Arrangements (Tables)	Network	*	*	http://www.transalta.com/role/JointArrangementsTables
506	Implied Table	Table	*	*	implied:Table
507	Disclosure of interests in other entities [Abstract]	Abstract			tac:DisclosureofinterestsinotherentitiesAbstract
508	Disclosure of interests in joint arrangements	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInterestsInJointArrangementsExplanatory
509	2391301 - Disclosure - Cash Flow Information (Tables)	Network	*	*	http://www.transalta.com/role/CashFlowInformationTables
510	Implied Table	Table	*	*	implied:Table
511	Disclosure of cash flow statement [Abstract]	Abstract			tac:DisclosureofcashflowstatementAbstract
512	Disclosure of non-cash operating working capital	Concept (Text Block (HTML))	For Period		tac:DisclosureofnoncashoperatingworkingcapitalTableTextBlock
513	Cash flows from (used in) operating activities [Text Block]	Concept (Text Block (HTML))	For Period		tac:CashflowsfromusedinoperatingactivitiesTextBlock
514	2394301 - Disclosure - Capital (Tables)	Network	*	*	http://www.transalta.com/role/CapitalTables
515	Implied Table	Table	*	*	implied:Table
516	Disclosure of notes and other explanatory information [Abstract]	Abstract			tac:DisclosureofnotesandotherexplanatoryinformationAbstract
517	Disclosure of share capital, reserves and other equity interest	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfShareCapitalReservesAndOtherEquityInterestExplanatory
518	Disclosure of investment grade credit rating	Concept (Text Block (HTML))	For Period		tac:DisclosureofinvestmentgradecreditratingTableTextBlock
519	Disclosure of cash flow statement	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfCashFlowStatementExplanatory
520	2397301 - Disclosure - Related Party Transactions (Tables)	Network	*	*	http://www.transalta.com/role/RelatedPartyTransactionsTables
521	Implied Table	Table	*	*	implied:Table
522	Related Party [Abstract]	Abstract			tac:RelatedPartyAbstract
523	Disclosure of interests in subsidiaries	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInterestsInSubsidiariesExplanatory
524	Disclosure of information about key management personnel	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesExplanatory
525	2398301 - Disclosure - Commitments and Contingencies (Tables)	Network	*	*	http://www.transalta.com/role/CommitmentsAndContingenciesTables
526	Implied Table	Table	*	*	implied:Table
527	Disclosure of other provisions, contingent liabilities and contingent assets [Abstract]	Abstract			tac:DisclosureofotherprovisionscontingentliabilitiesandcontingentassetsAbstract
528	Disclosure of commitments and future payments	Concept (Text Block (HTML))	For Period		tac:DisclosureofCommitmentsByCommitmentTableTextBlock
529	2398301 - Disclosure - Segment Disclosures (Tables)	Network	*	*	http://www.transalta.com/role/SegmentDisclosuresTables
530	Implied Table	Table	*	*	implied:Table
531	Disclosure of entity's operating segments [Abstract]	Abstract			tac:DisclosureofentitysoperatingsegmentsAbstract
532	Disclosure of operating segments	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfOperatingSegmentsExplanatory
533	Disclosure of selected consolidated statements of financial position information	Concept (Text Block (HTML))	For Period		tac:DisclosureofselectedconsolidatedstatementsoffinancialpositioninformationTableTextBlock
534	Disclosure of components in other non-current assets	Concept (Text Block (HTML))	For Period		tac:DisclosureofComponentsinOtherNoncurrentAssetsTableTextBlock
535	Disclosure of reconciliation between depreciation and amortization	Concept (Text Block (HTML))	For Period		tac:DisclosureofreconciliationbetweendepreciationandamortizationTableTextBlock
536	Disclosure of geographical areas	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfGeographicalAreasExplanatory
537	2401401 - Disclosure - Corporate Information Corporate Information (Details)	Network	*	*	http://www.transalta.com/role/CorporateInformationCorporateInformationDetails
538	Disclosure of operating segments [table]	Table	*	*	ifrs-full:DisclosureOfOperatingSegmentsTable
539	Segments [axis]	Axis			ifrs-full:SegmentsAxis
540	Segments [member]	Member			ifrs-full:SegmentsMember
541	Generation Segments [Member]	Member			tac:GenerationSegmentsMember
542	Disclosure of operating segments [line items]	LineItems			ifrs-full:DisclosureOfOperatingSegmentsLineItems
543	Number of segments	Concept (Integer)	As Of		tac:NumberOfReportableSegments1
544	2404403 - Disclosure - Significant Accounting Policies (Details)	Network	*	*	http://www.transalta.com/role/SignificantAccountingPoliciesDetails
545	Disclosure of detailed information about intangible assets [table]	Table	*	*	ifrs-full:DisclosureOfIntangibleAssetsTable
546	Classes of intangible assets and goodwill [axis]	Axis			ifrs-full:ClassesOfIntangibleAssetsAndGoodwillAxis
547	Intangible assets and goodwill [member]	Member			ifrs-full:IntangibleAssetsAndGoodwillMember
548	Computer software	Member			ifrs-full:ComputerSoftwareMember
549	Power sale contracts	Member			tac:PowerSaleContractsMember
550	Range [axis]	Axis			ifrs-full:RangeAxis
551	Ranges [member]	Member			ifrs-full:RangesMember
552	Minimum	Member			ifrs-full:BottomOfRangeMember
553	Maximum	Member			ifrs-full:TopOfRangeMember
554	Disclosure of detailed information about intangible assets [line items]	LineItems			ifrs-full:DisclosureOfIntangibleAssetsLineItems
555	Intangible assets, useful life	Concept (xbrli:durationItemType)	For Period		tac:IntangibleAssetsUsefulLife
556	2404403 - Disclosure - Significant Accounting Policies (Details)	Network	*	*	http://www.transalta.com/role/SignificantAccountingPoliciesDetails
557	Disclosure of detailed information about property, plant and equipment [table]	Table	*	*	ifrs-full:DisclosureOfPropertyPlantAndEquipmentTable
558	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
559	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
560	Coal generation	Member			tac:CoalGenerationMember
561	Gas generation	Member			tac:GasGenerationMember
562	Hydro	Member			tac:HydroGenerationMember
563	Wind Generation	Member			tac:WindGenerationMember
564	Mining property and equipment	Member			ifrs-full:MiningPropertyMember
565	Capital spares and other	Member			tac:CapitalSparesAndOtherMember
566	Facilities	Member			tac:FacilitiesMember
567	Range [axis]	Axis			ifrs-full:RangeAxis
568	Ranges [member]	Member			ifrs-full:RangesMember
569	Minimum	Member			ifrs-full:BottomOfRangeMember
570	Maximum	Member			ifrs-full:TopOfRangeMember
571	Disclosure of detailed information about property, plant and equipment [line items]	LineItems			ifrs-full:DisclosureOfPropertyPlantAndEquipmentLineItems
572	PP&E useful life	Concept (xbrli:durationItemType)	For Period		tac:PropertyPlantAndEquipmentUsefulLife1
573	2407402 - Disclosure - Accounting Changes - Narrative (Details)	Network	*	*	http://www.transalta.com/role/AccountingChangesNarrativeDetails
574	Disclosure of changes in accounting estimates [table]	Table	*	*	ifrs-full:DisclosureOfChangesInAccountingEstimatesTable
575	Range [axis]	Axis			ifrs-full:RangeAxis
576	Ranges [member]	Member			ifrs-full:RangesMember
577	Minimum	Member			ifrs-full:BottomOfRangeMember
578	Maximum	Member			ifrs-full:TopOfRangeMember
579	Financial effect of transition from previous GAAP to IFRSs [axis]	Axis			ifrs-full:FinancialEffectOfTransitionFromPreviousGAAPToIFRSsAxis
580	IFRSs [member]	Member			ifrs-full:IFRSsMember
581	Effect of transition to IFRSs [member]	Member			ifrs-full:EffectOfTransitionToIFRSsMember
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583	New IFRSs [member]	Member			ifrs-full:NewIFRSsMember
584	IFRS 15	Member			ifrs-full:IncreaseDecreaseDueToApplicationOfIFRS15Member
585	IFRS 16 [Member]	Member			tac:IFRS16Member
586	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
587	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
588	Alberta Mine	Member			tac:AlbertaMineMember
589	Sundance Unit 1	Member			tac:SundanceUnit1Member
590	Sundance Unit 2	Member			tac:SundanceUnit2Member
591	Accounting estimates [axis]	Axis			ifrs-full:AccountingEstimatesAxis
592	Accounting estimates [member]	Member			ifrs-full:AccountingEstimatesMember
593	Change in Useful Lives Estimate	Member			tac:ChangeinUsefulLivesEstimateMember
594	Disclosure of changes in accounting estimates [line items]	LineItems			ifrs-full:DisclosureOfChangesInAccountingEstimatesLineItems
595	IFRS 15 transition adjustment	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughCumulativeCatchupAdjustmentsToRevenueArisingFromChangeInEstimateOfTransactionPriceContractLiabilities
596	Contract liabilities (Note 5)	Concept (Monetary)	As Of	Credit	ifrs-full:ContractLiabilities
597	Deferred income tax liabilities (Note 11)	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredTaxLiabilities
598	Non-controlling interests (Note 12)	Concept (Monetary)	As Of	Credit	ifrs-full:NoncontrollingInterests
599	Deficit	Concept (Monetary)	As Of	Credit	ifrs-full:RetainedEarnings
600	Depreciation and amortization	Concept (Monetary)	For Period	Debit	ifrs-full:DepreciationAndAmortisationExpense
601	Right-of-use assets	Concept (Monetary)	As Of	Debit	ifrs-full:RightofuseAssets
602	Lease liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:LeaseLiabilities
603	2407403 - Disclosure - Accounting Changes - Disclosure of comparative information prepared under previous GAAP (Details)	Network	*	*	http://www.transalta.com/role/AccountingChangesDisclosureOfComparativeInformationPreparedUnderPreviousGaapDetails
604	Disclosure of comparative information prepared under previous GAAP [table]	Table	*	*	ifrs-full:DisclosureOfComparativeInformationPreparedUnderPreviousGAAPTable
605	Financial effect of transition from previous GAAP to IFRSs [axis]	Axis			ifrs-full:FinancialEffectOfTransitionFromPreviousGAAPToIFRSsAxis
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607	Previous GAAP [member]	Member			ifrs-full:PreviousGAAPMember
608	Effect of transition to IFRSs [member]	Member			ifrs-full:EffectOfTransitionToIFRSsMember
609	Disclosure of comparative information prepared under previous GAAP [line items]	LineItems			ifrs-full:DisclosureOfComparativeInformationPreparedUnderPreviousGAAPLineItems
610	Profit (loss) [abstract]	Abstract			ifrs-full:ProfitLossAbstract
611	Revenues	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromContractsWithCustomers
612	(Note 6)	Concept (Monetary)	For Period	Debit	ifrs-full:CostOfSales
613	Net interest expense	Concept (Monetary)	For Period	Debit	ifrs-full:InterestExpense
614	Net earnings (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
615	Statement of financial position [abstract]	Abstract			ifrs-full:StatementOfFinancialPositionAbstract
616	Deferred income tax liabilities (Note 11)	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredTaxLiabilities
617	Contract liability	Concept (Monetary)	As Of	Credit	ifrs-full:ContractLiabilities
618	Deficit	Concept (Monetary)	As Of	Credit	ifrs-full:RetainedEarnings
619	24100402 - Disclosure - Significant Events - Transition to Clean Power in Alberta (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsTransitionToCleanPowerInAlbertaDetails
620	Investment [Table]	Table	*	*	invest:InvestmentTable
621	Range [axis]	Axis			ifrs-full:RangeAxis
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624	Maximum	Member			ifrs-full:TopOfRangeMember
625	Counterparties [axis]	Axis			ifrs-full:CounterpartiesAxis
626	Counterparties [member]	Member			ifrs-full:CounterpartiesMember
627	Tidewater	Member			tac:TidewaterMidstreamandInfrastructureLtdMember
628	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
629	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
630	Gas conversion units	Member			tac:GasConversionUnitsMember
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632	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
633	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
634	Windrise [Member]	Member			tac:WindriseMember
635	Tidewater Brazeau River Pipeline	Member			tac:TidewaterBrazeauRiverPipelineMember
636	Sundance Power Plant	Member			tac:SundancePowerPlantMember
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638	Sundance Unit 1	Member			tac:SundanceUnit1Member
639	Sundance Unit 2	Member			tac:SundanceUnit2Member
640	Sundance Unit 3	Member			tac:SundanceUnit3Member
641	Sundance Unit 4	Member			tac:SundanceUnit4Member
642	Sundance Unit 5	Member			tac:SundanceUnit5Member
643	Investment [Line Items]	LineItems			invest:InvestmentLineItems
644	Capacity of facility (in megawatts)	Concept (num:powerItemType)	As Of		tac:CapacityOfPowerGenerationAssetsPower
645	Renewable electricity support agreement, term	Concept (xbrli:durationItemType)	For Period		tac:RenewableElectricitySupportAgreementTerm
646	Payments for development project expenditure	Concept (Monetary)	For Period	Credit	ifrs-full:PaymentsForDevelopmentProjectExpenditure
647	Future option to acquire pipeline, ownership percentage	Concept (Percent)	As Of		tac:OptiontoAcquirePipelineOwnershipPercentage
648	Natural gas pipeline, length (km)	Concept (num:lengthItemType)	As Of		tac:NaturalGasPipelineLength
649	Natural gas pipeline capacity (mmcf)	Concept (num:volumeItemType)	As Of		tac:NaturalGasPipelineCapacityVolume
650	Natural gas pipeline capacity, expansion capability (mmcf)	Concept (num:volumeItemType)	As Of		tac:NaturalGasPipelineCapacityExpansionCapabilityVolume
651	Number of pipelines needed to reduce operational risk (at least)	Concept (Integer)	For Period		tac:NumberofPipelinesNeededtoReduceOperationalRisk
652	Transition to gas and renewables generation, mothballing term	Concept (xbrli:durationItemType)	For Period		tac:TransitiontoGasandRenewablesGenerationMothballingTerm
653	Impairment loss	Concept (Monetary)	For Period	Debit	ifrs-full:ImpairmentLoss
654	Impairment loss recognised in profit or loss	Concept (Monetary)	For Period	Debit	ifrs-full:ImpairmentLossRecognisedInProfitOrLoss
655	24100403 - Disclosure - Significant Events - Kent Hills 3 Wind Project (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsKentHills3WindProjectDetails
656	Investment [Table]	Table	*	*	invest:InvestmentTable
657	Counterparties [axis]	Axis			ifrs-full:CounterpartiesAxis
658	Counterparties [member]	Member			ifrs-full:CounterpartiesMember
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660	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
661	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
662	Kent Hills 3 Wind Project	Member			tac:KentHills3WindProjectMember
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664	Capacity of facility (in megawatts)	Concept (num:powerItemType)	As Of		tac:CapacityOfPowerGenerationAssetsPower
665	Increase in contractual power capacity (in megawatts)	Concept (num:powerItemType)	For Period		tac:IncreaseDecreaseinContractualPowerCapacityPower
666	24100404 - Disclosure - Significant Events - TransAlta Renewables Project Financing of New Brunswick (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsTransaltaRenewablesProjectFinancingOfNewBrunswickDetails
667	Investment [Table]	Table	*	*	invest:InvestmentTable
668	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
669	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
670	Bond, 4.454%, November 2033 maturity	Member			tac:Bond4.454PercentNovember2033MaturityMember
671	Unsecured debentures	Member			tac:UnsecuredDebt1Member
672	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
673	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
674	Kent Hills Wind L.P.	Member			tac:KentHillsWindL.P.Member
675	Canadian Hydro Developers Inc.	Member			tac:CanadianHydroDevelopersInc.Member
676	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
677	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
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679	Legal Entity [Axis]	Axis			dei:LegalEntityAxis
680	Entity [Domain]	Member			dei:EntityDomain
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684	Interest rate	Concept (Percent)	As Of		ifrs-full:BorrowingsInterestRate
685	Increase in contractual power capacity (in megawatts)	Concept (num:powerItemType)	For Period		tac:IncreaseDecreaseinContractualPowerCapacityPower
686	Proportion of ownership interests held by non-controlling interests	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestsHeldByNoncontrollingInterests
687	Restricted cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:RestrictedCashAndCashEquivalents
688	Proceeds from non-current borrowings	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromNoncurrentBorrowings
689	Redemption of unsecured debt	Concept (Monetary)	For Period	Credit	tac:RedemptionofNoncurrentBorrowings
690	Redemption of unsecured debt, principal	Concept (Monetary)	For Period	Credit	tac:RedemptionofNoncurrentBorrowingsPrincipal
691	Redemption of unsecured debt, premium	Concept (Monetary)	For Period	Credit	tac:RedemptionofNoncurrentBorrowingsPremium
692	Redemption of unsecured debt, accrued interest	Concept (Monetary)	For Period	Credit	tac:RedemptionofNoncurrentBorrowingsAccruedInterest
693	24100405 - Disclosure - Significant Events - Force Majeure Relief (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsForceMajeureReliefDetails
694	Disclosure of other provisions [table]	Table	*	*	ifrs-full:DisclosureOfOtherProvisionsTable
695	Classes of other provisions [axis]	Axis			ifrs-full:ClassesOfProvisionsAxis
696	Other provisions [member]	Member			ifrs-full:OtherProvisionsMember
697	Force Majeure Relief Claim	Member			tac:ForceMajeureReliefClaimMember
698	Disclosure of other provisions [line items]	LineItems			ifrs-full:DisclosureOfOtherProvisionsLineItems
699	Reversal of unused provision	Concept (Monetary)	For Period	Debit	ifrs-full:UnusedProvisionReversedOtherProvisions
700	24100406 - Disclosure - Significant Events - Poplar Creek Financing (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsPoplarCreekFinancingDetails
701	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
702	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
703	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
704	TAPC Holdings	Member			tac:TAPCHoldingsL.P.Member
705	Types of interest rates [axis]	Axis			ifrs-full:TypesOfInterestRatesAxis
706	Interest rate types [member]	Member			ifrs-full:InterestRateTypesMember
707	Floating interest rate [member]	Member			ifrs-full:FloatingInterestRateMember
708	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
709	Aggregate principle amount of senior secured bonds issued	Concept (Monetary)	As Of	Credit	ifrs-full:BondsIssued
710	Basis spread on variable rate	Concept (Percent)	As Of		ifrs-full:BorrowingsAdjustmentToInterestRateBasis
711	24100407 - Disclosure - Significant Events - Wintering Hills Assets Held for Sale (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsWinteringHillsAssetsHeldForSaleDetails
712	Disclosure of impairment loss and reversal of impairment loss [table]	Table	*	*	ifrs-full:DisclosureOfImpairmentLossAndReversalOfImpairmentLossTable
713	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
714	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
715	Wintering Hills	Member			tac:WinteringHillsMember
716	Segments [axis]	Axis			ifrs-full:SegmentsAxis
717	Segments [member]	Member			ifrs-full:SegmentsMember
718	Wind and Solar	Member			tac:WindandSolarMember
719	Disclosure of impairment loss and reversal of impairment loss [line items]	LineItems			ifrs-full:DisclosureOfImpairmentLossAndReversalOfImpairmentLossLineItems
720	Decrease through classified as held for sale, investment property	Concept (Monetary)	For Period	Credit	ifrs-full:DecreaseThroughClassifiedAsHeldForSaleInvestmentProperty
721	Proceeds from sale of assets held for sale	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromDisposalOfNoncurrentAssetsOrDisposalGroupsClassifiedAsHeldForSaleAndDiscontinuedOperations
722	24100408 - Disclosure - Significant Events - Financing of a Quebec Wind Asset by TransAlta Renewables (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsFinancingOfQuebecWindAssetByTransaltaRenewablesDetails
723	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
724	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
725	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
726	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
727	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
728	Bonds issued	Concept (Monetary)	As Of	Credit	ifrs-full:BondsIssued
729	Interest rate	Concept (Percent)	As Of		ifrs-full:BorrowingsInterestRate
730	24100409 - Disclosure - Significant Events - Investment in and Acquisition by TransAlta Renewables of the Canadian Assets (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsInvestmentInAndAcquisitionByTransaltaRenewablesOfCanadianAssetsDetails
731	Disclosure of detailed information about business combination [table]	Table	*	*	ifrs-full:DisclosureOfBusinessCombinationsTable
732	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
733	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
734	Convertible unsecured debenture	Member			tac:ConvertibleUnsecuredSubordinatedDebentureDueDecember2020Member
735	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
736	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
737	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
738	Business combinations [axis]	Axis			ifrs-full:BusinessCombinationsAxis
739	Entity's total for business combinations [member]	Member			ifrs-full:EntitysTotalForBusinessCombinationsMember
740	Canadian Assets	Member			tac:SarniaCogenerationPlantLeNordaisWindFarmAndRaggedChuteHydroFacilityCanadianAssetsMember
741	Disclosure of detailed information about business combination [line items]	LineItems			ifrs-full:DisclosureOfBusinessCombinationsLineItems
742	Aggregate value of business combination	Concept (Monetary)	As Of	Credit	ifrs-full:AcquisitiondateFairValueOfTotalConsiderationTransferred
743	Capacity of facility (in megawatts)	Concept (num:powerItemType)	As Of		tac:CapacityOfPowerGenerationAssetsPower
744	Cash paid	Concept (Monetary)	As Of	Credit	ifrs-full:CashTransferred
745	Common shares issued (in shares)	Concept (Decimal)	As Of		ifrs-full:NumberOfInstrumentsOrInterestsIssuedOrIssuable
746	Value of common shares issued	Concept (Monetary)	As Of	Credit	ifrs-full:EquityInterestsOfAcquirer
747	Notes and debentures issued	Concept (Monetary)	As Of	Credit	ifrs-full:NotesAndDebenturesIssued
748	Repayments of bonds, notes and debentures	Concept (Monetary)	For Period	Credit	ifrs-full:RepaymentsOfBondsNotesAndDebentures
749	Payment of accrued interest	Concept (Monetary)	For Period	Credit	tac:Paymentofaccruedinterest
750	Subscription receipts (in shares)	Concept (Shares)	As Of		tac:CommonStockSubscriptionsIssuedShares
751	Price per subscription receipt	Concept (Monetary)	As Of	Debit	tac:PricePerCommonStockSubscriptionReceipt
752	Number of shares received per subscription receipt (in shares)	Concept (Shares)	For Period		tac:NumberOfSharesReceivedPerCommonShareSubscriptionReceipt
753	Dividend per subscription receipt (in CAD per share)	Concept (Share)	For Period		ifrs-full:DividendsPaidOrdinarySharesPerShare
754	Number of shares issued	Concept (Shares)	As Of		ifrs-full:NumberOfSharesIssued
755	Dividends paid, ordinary shares	Concept (Monetary)	For Period	Debit	ifrs-full:DividendsPaidOrdinaryShares
756	Share issue related cost	Concept (Monetary)	For Period	Debit	ifrs-full:ShareIssueRelatedCost
757	Effect of share issuance cost on income cost	Concept (Monetary)	For Period	Credit	tac:ShareIssueRelatedCostEffectOnIncomeTaxRecovery
758	Working capital and certain capital spares acquired	Concept (Monetary)	As Of	Debit	tac:WorkingCapitalAndCapitalSparesAcquired
759	Transfer of equity from non-controlling interests	Concept (Monetary)	As Of	Credit	tac:TransferOfEquityFromNonControllingInterests
760	24100410 - Disclosure - Significant Events - Restructured Poplar Creek Contract and Acquisition of Wind Farms (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsRestructuredPoplarCreekContractAndAcquisitionOfWindFarmsDetails
761	Disclosure of detailed information about business combination [table]	Table	*	*	ifrs-full:DisclosureOfBusinessCombinationsTable
762	Counterparties [axis]	Axis			ifrs-full:CounterpartiesAxis
763	Counterparties [member]	Member			ifrs-full:CounterpartiesMember
764	Suncor Energy	Member			tac:SuncorEnergyMember
765	Classes of assets [axis]	Axis			ifrs-full:ClassesOfAssetsAxis
766	Assets [member]	Member			ifrs-full:ClassesOfAssetsMember
767	Finance lease receivables	Member			ifrs-full:LeaseReceivablesMember
768	Maturity [axis]	Axis			ifrs-full:MaturityAxis
769	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
770	2016 to 2018	Member			tac:AnnuallyFrom2016To2018Member
771	2019 to 2030	Member			tac:AnnuallyFrom2019To2030Member
772	Business combinations [axis]	Axis			ifrs-full:BusinessCombinationsAxis
773	Entity's total for business combinations [member]	Member			ifrs-full:EntitysTotalForBusinessCombinationsMember
774	Poplar Creek	Member			tac:PoplarCreekMember
775	Wind Farms	Member			tac:KentBreezeAndWinteringHillsFacilitiesTheWindFarmsMember
776	Kent Breeze	Member			tac:KentBreezeWindFarmMember
777	Wintering Hills	Member			tac:WinteringHillsMember
778	Range [axis]	Axis			ifrs-full:RangeAxis
779	Ranges [member]	Member			ifrs-full:RangesMember
780	Maximum	Member			ifrs-full:TopOfRangeMember
781	Disclosure of detailed information about business combination [line items]	LineItems			ifrs-full:DisclosureOfBusinessCombinationsLineItems
782	Capacity of facility (in megawatts)	Concept (num:powerItemType)	As Of		tac:CapacityOfPowerGenerationAssetsPower
783	Number of turbines acquired	Concept (Integer)	As Of		tac:NumberOfTurbinesAcquired
784	Number of turbines retained	Concept (Integer)	As Of		tac:NumberOfTurbinesRetained
785	Number of wind farms acquired	Concept (Integer)	As Of		tac:NumberOfWindFarmsAcquired
786	Ownership interest (as a percent)	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInSubsidiary
787	Assets	Abstract			ifrs-full:AssetsAbstract
788	Finance lease receivable	Concept (Monetary)	As Of	Debit	tac:FinanceLeaseReceivableRecognisedAsOfAcquisitionDate
789	Property, plant, and equipment	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipmentRecognisedAsOfAcquisitionDate
790	Intangibles	Concept (Monetary)	As Of	Debit	ifrs-full:IdentifiableIntangibleAssetsRecognisedAsOfAcquisitionDate
791	Net working capital	Concept (Monetary)	As Of	Debit	tac:NetWorkingCapitalRecognisedAsOfAcquisitionDate
792	Total assets acquired	Concept (Monetary)	As Of	Debit	tac:AssetsRecognisedAsOfAcquisitionDate
793	Liabilities	Abstract			ifrs-full:LiabilitiesAbstract
794	Decomissioning and restoration provision	Concept (Monetary)	As Of	Credit	tac:DecommissioningAndRestorationProvisionRecognisedAsOfAcquisitionDate
795	Net assets acquired	Concept (Monetary)	As Of	Debit	ifrs-full:IdentifiableAssetsAcquiredLiabilitiesAssumed
796	Consideration transferred	Abstract			ifrs-full:AcquisitiondateFairValueOfTotalConsiderationTransferredAbstract
797	Property, plant, and equipment	Concept (Monetary)	As Of	Credit	tac:PropertyPlantAndEquipmentTransferredAcquisitionDateFairValue
798	Net working capital	Concept (Monetary)	As Of	Credit	tac:NetWorkingCapitalTransferredAcquisitionDateFairValue
799	Decommissioning and restoration provision	Concept (Monetary)	As Of	Debit	tac:DecommissioningAndRestorationProvisionTransferredAcquisitionDateFairValue
800	Carrying amount of transferred net assets	Concept (Monetary)	As Of	Credit	ifrs-full:AcquisitiondateFairValueOfTotalConsiderationTransferred
801	Gain recognised in bargain purchase transaction	Concept (Monetary)	For Period	Credit	ifrs-full:GainRecognisedInBargainPurchaseTransaction
802	Finance lease receivables	Concept (Monetary)	As Of	Debit	ifrs-full:FinanceLeaseReceivables
803	Discount rate	Concept (Percent)	As Of		ifrs-full:DescriptionOfDiscountRatesUsedInCurrentEstimateOfValueInUse
804	Increase (decrease) in revenues	Concept (Monetary)	For Period	Credit	tac:Increasedecreaseinrevenuesofcombinedentity
805	Increase (decrease) in earnings, before tax	Concept (Monetary)	For Period	Credit	tac:Increasedecreaseinearningsofcombinedentitybeforetax
806	24100412 - Disclosure - Significant Events - Sale of Economic Interest in Australian Assets to TransAlta Renewables Inc. (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsSaleOfEconomicInterestInAustralianAssetsToTransaltaRenewablesIncDetails
807	Disclosure of detailed information about business combination [table]	Table	*	*	ifrs-full:DisclosureOfBusinessCombinationsTable
808	Classes of ordinary shares [axis]	Axis			ifrs-full:ClassesOfOrdinarySharesAxis
809	Common shares	Member			ifrs-full:OrdinarySharesMember
810	Class B shares	Member			tac:ClassBsharesMember
811	Common shares	Member			tac:CommonsharesMember
812	Counterparties [axis]	Axis			ifrs-full:CounterpartiesAxis
813	Counterparties [member]	Member			ifrs-full:CounterpartiesMember
814	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
815	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
816	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
817	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
818	Business combinations [axis]	Axis			ifrs-full:BusinessCombinationsAxis
819	Entity's total for business combinations [member]	Member			ifrs-full:EntitysTotalForBusinessCombinationsMember
820	Australian Assets	Member			tac:AustralianAssetsMember
821	Disclosure of detailed information about business combination [line items]	LineItems			ifrs-full:DisclosureOfBusinessCombinationsLineItems
822	Capacity of facility (in megawatts)	Concept (num:powerItemType)	As Of		tac:CapacityOfPowerGenerationAssetsPower
823	Number of operating assets	Concept (Integer)	As Of		tac:NumberOfOperatingAssets
824	Length of pipeline	Concept (Pure)	As Of		tac:LengthOfPipeline
825	Consideration received	Concept (Monetary)	For Period	Credit	ifrs-full:ConsiderationPaidReceived
826	Cash consideration received	Concept (Monetary)	For Period	Credit	ifrs-full:PortionOfConsiderationPaidReceivedConsistingOfCashAndCashEquivalents
827	Value of equity consideration received	Concept (Monetary)	For Period	Credit	tac:PortionOfConsiderationPaidReceivedConsistingOfEquityInterests
828	Shares offered for conversion	Concept (Shares)	As Of		tac:Sharesofferedforconversion
829	Equity securities received upon conversion of shares	Concept (Shares)	As Of		tac:Equitysecuritiesreceiveduponconversionofshares
830	Proportion of equity participation in subsidiary	Concept (Percent)	For Period		tac:ProportionOfEquityParticipationInSubsidiary
831	Target costs of construction and commissioning of assets	Concept (Monetary)	For Period	Debit	tac:EstimatedCostsOfConstructionAndCommissioningOfAssets
832	Common shares issued (in shares)	Concept (Decimal)	As Of		ifrs-full:NumberOfInstrumentsOrInterestsIssuedOrIssuable
833	Share price	Concept (Monetary)	As Of	Credit	tac:SharePriceAtIssuance
834	Proceeds from issuing shares	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromIssuingShares
835	Value of common shares issued	Concept (Monetary)	As Of	Credit	ifrs-full:EquityInterestsOfAcquirer
836	Share issue related cost	Concept (Monetary)	For Period	Debit	ifrs-full:ShareIssueRelatedCost
837	Effect of share issuance cost on income cost	Concept (Monetary)	For Period	Credit	tac:ShareIssueRelatedCostEffectOnIncomeTaxRecovery
838	Dividend-equivalent payments	Concept (Monetary)	For Period	Credit	tac:DividendEquivalentPayments
839	24100413 - Disclosure - Significant Events - Sale of TransAlta Renewables Shares to Alberta Investment Management Corporation (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsSaleOfTransaltaRenewablesSharesToAlbertaInvestmentManagementCorporationDetails
840	Disclosure of subsidiaries [table]	Table	*	*	ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesTable
841	Long-Term Debt, Type [Axis]	Axis			tac:LongTermDebtTypeAxis
842	Long-Term Debt, Type [Domain]	Member			tac:LongTermDebtTypeDomain
843	Non-recourse	Member			tac:NonRecourseDebtMember
844	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
845	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
846	3.834% Non-Recourse Bond due 2028	Member			tac:A3.834NonRecourseBondDue2028Member
847	Non-Recourse Bonds	Member			tac:NonRecourseBondsMember
848	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
849	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
850	Melancthon-Wolfe Wind	Member			tac:MelancthonWolfeWindL.PMember
851	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
852	Disclosure of subsidiaries [line items]	LineItems			ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesLineItems
853	Notional amount	Concept (Monetary)	As Of		ifrs-full:NotionalAmount
854	Common shares of subsidiary transferred	Concept (Shares)	As Of		tac:SharesOfSubsidiarySoldThatDoNotResultInLossOfControl
855	(Note 4)	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromChangesInOwnershipInterestsInSubsidiaries
856	Net proceeds from sale of ownership interest	Concept (Monetary)	For Period	Debit	tac:NetProceedsFromChangesInOwnershipInterestsInSubsidiariesThatDoNotResultInLossOfControl
857	Restricted cash (Note 22)	Concept (Monetary)	As Of	Debit	ifrs-full:RestrictedCashAndCashEquivalents
858	Redemption of unsecured debt	Concept (Monetary)	For Period	Credit	tac:RedemptionofNoncurrentBorrowings
859	24100414 - Disclosure - Significant Events - Changes in Internal Capitalization of U.S. Entities (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsChangesInInternalCapitalizationOfUSEntitiesDetails
860	Disclosure of detailed information about hedges [table]	Table	*	*	ifrs-full:DisclosureOfHedgeAccountingTable
861	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
862	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
863	U.S. Entities	Member			tac:U.S.EntitiesMember
864	Types of hedges [axis]	Axis			ifrs-full:TypesOfHedgesAxis
865	Hedges [member]	Member			ifrs-full:TypesOfHedgesMember
866	Net investment hedges	Member			ifrs-full:HedgesOfNetInvestmentInForeignOperationsMember
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868	Reclassification of cumulative translation gains from OCI	Concept (Monetary)	For Period	Debit	ifrs-full:ReclassificationAdjustmentsOnHedgesOfNetInvestmentsInForeignOperationsBeforeTax
869	Cumulative after-tax losses on net investment hedge	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnHedgesOfNetInvestmentsInForeignOperationsBeforeTax
870	Gains (losses) on hedges of net investments in foreign operations, net of tax	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnHedgesOfNetInvestmentsInForeignOperationsNetOfTax
871	24100415 - Disclosure - Significant Events - Acquisition of Two US Wind Projects (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsAcquisitionOfTwoUsWindProjectsDetails
872	Investment [Table]	Table	*	*	invest:InvestmentTable
873	Non-adjusting events after reporting period [axis]	Axis			ifrs-full:NonadjustingEventsAfterReportingPeriodAxis
874	Non-adjusting events after reporting period [member]	Member			ifrs-full:NonadjustingEventsMember
875	Funding Of Construction Costs [Member]	Member			tac:FundingOfConstructionCostsMember
876	Counterparties [axis]	Axis			ifrs-full:CounterpartiesAxis
877	Counterparties [member]	Member			ifrs-full:CounterpartiesMember
878	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
879	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
880	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
881	US Wind Projects [Member]	Member			tac:USWindProjectsMember
882	US Wind Projects - Big Level [Member]	Member			tac:USWindProjectsBigLevelMember
883	US Wind Projects - Antrim [Member]	Member			tac:USWindProjectsAntrimMember
884	Investment [Line Items]	LineItems			invest:InvestmentLineItems
885	Capacity of facility (in megawatts)	Concept (num:powerItemType)	As Of		tac:CapacityOfPowerGenerationAssetsPower
886	Number of power purchase arrangements	Concept (Integer)	For Period		tac:NumberofPowerPurchaseArrangements
887	Term of power purchase arrangement	Concept (xbrli:durationItemType)	For Period		tac:TermOfPowerPurchaseArrangements
888	Notes and debentures issued	Concept (Monetary)	As Of	Credit	ifrs-full:NotesAndDebenturesIssued
889	Payments for development project expenditure	Concept (Monetary)	For Period	Credit	ifrs-full:PaymentsForDevelopmentProjectExpenditure
890	24100416 - Disclosure - Significant Events - TransAlta Renewables Acquires Three Renewable Assets from the Corporation (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsTransaltaRenewablesAcquiresThreeRenewableAssetsFromCorporationDetails
891	Investment [Table]	Table	*	*	invest:InvestmentTable
892	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
893	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
894	Property, plant, and equipment	Member			tac:PropertyPlantsAndEquipmentMember
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896	Counterparties [axis]	Axis			ifrs-full:CounterpartiesAxis
897	Counterparties [member]	Member			ifrs-full:CounterpartiesMember
898	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
899	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
900	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
901	Lakeswind Wind Farm	Member			tac:LakeswindWindFarmMember
902	Lakeswind Solar Projects	Member			tac:LakeswindSolarProjectsMember
903	Kent Breeze	Member			tac:KentBreezeWindFarmMember
904	Three Renewable Assets	Member			tac:ThreeRenewableAssetsMember
905	Lakeswind	Member			tac:LakeswindMember
906	Investment [Line Items]	LineItems			invest:InvestmentLineItems
907	Capacity of facility (in megawatts)	Concept (num:powerItemType)	As Of		tac:CapacityOfPowerGenerationAssetsPower
908	Consideration received	Concept (Monetary)	For Period	Credit	ifrs-full:ConsiderationPaidReceived
909	Value of equity consideration received	Concept (Monetary)	For Period	Credit	tac:PortionOfConsiderationPaidReceivedConsistingOfEquityInterests
910	Portion of consideration paid (received) consisting of cash and cash equivalents	Concept (Monetary)	For Period	Credit	ifrs-full:PortionOfConsiderationPaidReceivedConsistingOfCashAndCashEquivalents
911	Transfer of equity from non-controlling interests	Concept (Monetary)	As Of	Credit	tac:TransferOfEquityFromNonControllingInterests
912	Issued preferred capital	Concept (Monetary)	As Of	Credit	tac:IssuedPreferredCapital
913	Impairment loss	Concept (Monetary)	For Period	Debit	ifrs-full:ImpairmentLoss
914	24100417 - Disclosure - Significant Events - TransAlta Renewables Closes Offering of Common Shares (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsTransaltaRenewablesClosesOfferingOfCommonSharesDetails
915	Disclosure of components of capital [Table]	Table	*	*	tac:DisclosureofcomponentsofcapitalTable
916	Counterparties [axis]	Axis			ifrs-full:CounterpartiesAxis
917	Counterparties [member]	Member			ifrs-full:CounterpartiesMember
918	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
919	Disclosure of components of capital [Line Items]	LineItems			tac:DisclosureofcomponentsofcapitalLineItems
920	Issued preferred capital	Concept (Monetary)	As Of	Credit	tac:IssuedPreferredCapital
921	Number of shares issued	Concept (Shares)	As Of		ifrs-full:NumberOfSharesIssued
922	Par value per share	Concept (Share)	As Of		ifrs-full:ParValuePerShare
923	Gross Proceeds From Changes In Ownership Interests In Subsidiaries That Do Not Result In Loss Of Control	Concept (Monetary)	For Period	Debit	tac:GrossProceedsFromChangesInOwnershipInterestsInSubsidiariesThatDoNotResultInLossOfControl
924	Issued capital (Note 24)	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
925	Net proceeds on sale of non-controlling interest in subsidiary (Note 4)	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromChangesInOwnershipInterestsInSubsidiaries
926	Entity common stock, shares outstanding	Concept (Shares)	As Of		ifrs-full:NumberOfSharesOutstanding
927	Ownership interest (as a percent)	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInSubsidiary
928	24100418 - Disclosure - Significant Events - Million Dollar Financing (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsMillionDollarFinancingDetails
929	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
930	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
931	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
932	Unsecured debentures	Member			tac:UnsecuredDebt1Member
933	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
934	Bonds issued	Concept (Monetary)	As Of	Credit	ifrs-full:BondsIssued
935	Borrowings, interest rate basis	Concept (Text/String)	For Period		ifrs-full:BorrowingsInterestRateBasis
936	Alberta Off-Coal Agreement	Concept (Monetary)	For Period	Credit	tac:GainsLossesonContractAgreement
937	Alberta off-coal agreement, annual cash payments, net	Concept (Monetary)	For Period	Credit	tac:GainsLossesonContractAgreementNet
938	Interest rate	Concept (Percent)	As Of		ifrs-full:BorrowingsInterestRate
939	24100419 - Disclosure - Significant Events - Normal Course Issuer Bid (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsNormalCourseIssuerBidDetails
940	Disclosure of classes of share capital [table]	Table	*	*	ifrs-full:DisclosureOfClassesOfShareCapitalTable
941	Classes of share capital [axis]	Axis			ifrs-full:ClassesOfShareCapitalAxis
942	Share capital [member]	Member			ifrs-full:ClassesOfShareCapitalMember
943	NCIB Program	Member			tac:NCIBProgramMember
944	Disclosure of classes of share capital [line items]	LineItems			ifrs-full:DisclosureOfClassesOfShareCapitalLineItems
945	Stock purchase agreement, number of shares authorized	Concept (Shares)	As Of		tac:StockPurchaseAgreementSharesNumberAuthorized
946	Stock purchase agreement, maximum shares purchase for a single trading day	Concept (Shares)	For Period		tac:StockPurchaseAgreementMaximumSharesPurchasedForASingleTradingDay
947	Stock purchase agreement, Toronto Stock Exchange, twenty-five percent of daily trading volume	Concept (Shares)	For Period		tac:StockPurchaseAgreementTorontoStockExchangeTwentyFivePercentOfDailyTradingVolume
948	Restricted cash (Note 22)	Concept (Monetary)	As Of	Debit	ifrs-full:RestrictedCashAndCashEquivalents
949	Number of shares issued and fully paid	Concept (Shares)	As Of		ifrs-full:NumberOfSharesIssuedAndFullyPaid
950	Par value per share	Concept (Share)	As Of		ifrs-full:ParValuePerShare
951	Issued capital (Note 24)	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
952	24100420 - Disclosure - Significant Events - Other Narrative Disclosures (Details)	Network	*	*	http://www.transalta.com/role/SignificantEventsOtherNarrativeDisclosuresDetails
953	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
954	Segments [axis]	Axis			ifrs-full:SegmentsAxis
955	Segments [member]	Member			ifrs-full:SegmentsMember
956	Canadian Coal	Member			tac:CanadianCoalMember
957	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
958	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
959	Solomon Power Station	Member			tac:SolomonPowerStationMember
960	Counterparties [axis]	Axis			ifrs-full:CounterpartiesAxis
961	Counterparties [member]	Member			ifrs-full:CounterpartiesMember
962	Fortescue Metals Group Limited	Member			tac:FortescueMetalsGroupLimitedMember
963	Types of contracts [axis]	Axis			ifrs-full:TypesOfContractsAxis
964	Types of contracts [member]	Member			ifrs-full:TypesOfContractsMember
965	Power Purchase Arrangement	Member			tac:PowerPurchaseArrangementMember
966	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
967	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
968	Debentures	Member			tac:UnsecuredDebt1Member
969	6.65% Senior notes, due May 2018	Member			tac:SeniorNotes500Million6.65PercentDueMay2018Member
970	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
971	Portion of consideration paid (received) consisting of cash and cash equivalents	Concept (Monetary)	For Period	Credit	ifrs-full:PortionOfConsiderationPaidReceivedConsistingOfCashAndCashEquivalents
972	Interest rate	Concept (Percent)	As Of		ifrs-full:BorrowingsInterestRate
973	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
974	Redemption of unsecured debt	Concept (Monetary)	For Period	Credit	tac:RedemptionofNoncurrentBorrowings
975	Redemption of unsecured debt, premium	Concept (Monetary)	For Period	Credit	tac:RedemptionofNoncurrentBorrowingsPremium
976	Balancing Pool compensation estimate, termination of contractual arrangement	Concept (Monetary)	As Of	Debit	tac:CounterpartyCompensationEstimateTerminationofContractualArrangement
977	Consideration received	Concept (Monetary)	For Period	Credit	ifrs-full:ConsiderationPaidReceived
978	Government Agreements, Amount	Concept (Monetary)	For Period	Credit	tac:GovernmentAgreementsAmount
979	2410402 - Disclosure - Revenue (Details)	Network	*	*	http://www.transalta.com/role/RevenueDetails
980	Disclosure of disaggregation of revenue from contracts with customers [table]	Table	*	*	ifrs-full:DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersTable
981	Range [axis]	Axis			ifrs-full:RangeAxis
982	Ranges [member]	Member			ifrs-full:RangesMember
983	Minimum	Member			ifrs-full:BottomOfRangeMember
984	Maximum	Member			ifrs-full:TopOfRangeMember
985	Maturity [axis]	Axis			ifrs-full:MaturityAxis
986	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
987	Later than one year	Member			ifrs-full:LaterThanOneYearMember
988	Segment consolidation items [axis]	Axis			ifrs-full:SegmentConsolidationItemsAxis
989	Entity's total for segment consolidation items [member]	Member			ifrs-full:EntitysTotalForSegmentConsolidationItemsMember
990	Canadian Coal	Member			tac:CanadianCoalMember
991	Canadian Gas	Member			tac:CanadianGasMember
992	Australian Gas	Member			tac:AustralianGasMember
993	Wind and Solar	Member			tac:WindandSolarMember
994	Hydro	Member			tac:HydroMember
995	Disclosure of disaggregation of revenue from contracts with customers [line items]	LineItems			ifrs-full:DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems
996	Transaction price allocated to remaining performance obligations	Concept (Monetary)	As Of	Credit	ifrs-full:TransactionPriceAllocatedToRemainingPerformanceObligations
997	Revenue from performance obligations satisfied or partially satisfied in previous periods	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromPerformanceObligationsSatisfiedOrPartiallySatisfiedInPreviousPeriods
998	Revenue from performance obligations satisfied or partially satisfied in previous periods, term	Concept (xbrli:durationItemType)	For Period		tac:RevenueFromPerformanceObligationsSatisfiedOrPartiallySatisfiedInPreviousPeriodsTerm
999	2410403 - Disclosure - Revenue Disaggregation of Revenue (Details)	Network	*	*	http://www.transalta.com/role/RevenueDisaggregationOfRevenueDetails
1000	Disclosure of disaggregation of revenue from contracts with customers [table]	Table	*	*	ifrs-full:DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersTable
1001	Segment consolidation items [axis]	Axis			ifrs-full:SegmentConsolidationItemsAxis
1002	Entity's total for segment consolidation items [member]	Member			ifrs-full:EntitysTotalForSegmentConsolidationItemsMember
1003	Canadian Coal	Member			tac:CanadianCoalMember
1004	United States Coal	Member			tac:UnitedStatesCoalMember
1005	Canadian Gas	Member			tac:CanadianGasMember
1006	Australian Gas	Member			tac:AustralianGasMember
1007	Wind and Solar	Member			tac:WindandSolarMember
1008	Hydro	Member			tac:HydroMember
1009	Energy Marketing	Member			tac:EnergyMarketingMember
1010	Corporate	Member			tac:Corporate1Member
1011	Products and services [axis]	Axis			ifrs-full:ProductsAndServicesAxis
1012	Products and services [member]	Member			ifrs-full:ProductsAndServicesMember
1013	Contract With Customers [Member]	Member			tac:ContractWithCustomersMember
1014	Lease Income [Member]	Member			tac:LeaseIncomeMember
1015	Derivatives Income [Member]	Member			tac:DerivativesIncomeMember
1016	Government Incentives [Member]	Member			tac:GovernmentIncentivesMember
1017	Others	Member			tac:OthersMember
1018	Timing of transfer of goods or services [axis]	Axis			ifrs-full:TimingOfTransferOfGoodsOrServicesAxis
1019	Timing of transfer of goods or services [member]	Member			ifrs-full:TimingOfTransferOfGoodsOrServicesMember
1020	Goods or services transferred at point in time [member]	Member			ifrs-full:GoodsOrServicesTransferredAtPointInTimeMember
1021	Goods or services transferred over time [member]	Member			ifrs-full:GoodsOrServicesTransferredOverTimeMember
1022	Disclosure of disaggregation of revenue from contracts with customers [line items]	LineItems			ifrs-full:DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems
1023	Revenues	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromContractsWithCustomers
1024	Contingent rents recognised as income, classified as operating lease	Concept (Monetary)	For Period	Credit	ifrs-full:ContingentRentsRecognisedAsIncomeClassifiedAsOperatingLease
1025	2410404 - Disclosure - Revenue Contract Balances (Details)	Network	*	*	http://www.transalta.com/role/RevenueContractBalancesDetails
1026	Disclosure of disaggregation of revenue from contracts with customers [table]	Table	*	*	ifrs-full:DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersTable
1027	New IFRSs [axis]	Axis			ifrs-full:NewIFRSsAxis
1028	New IFRSs [member]	Member			ifrs-full:NewIFRSsMember
1029	IFRS 15	Member			ifrs-full:IncreaseDecreaseDueToApplicationOfIFRS15Member
1030	Disclosure of disaggregation of revenue from contracts with customers [line items]	LineItems			ifrs-full:DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems
1031	Changes in Contract Liabilities [Roll Forward]	Abstract			tac:ChangesinContractLiabilitiesRollForward
1032	Dec. 31, 2017	Concept (Monetary)	As Of	Credit	ifrs-full:ContractLiabilities
1033	IFRS 15 transition adjustment	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughCumulativeCatchupAdjustmentsToRevenueArisingFromChangeInEstimateOfTransactionPriceContractLiabilities
1034	Amounts transferred to revenue included in opening balance	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueThatWasIncludedInContractLiabilityBalanceAtBeginningOfPeriod
1035	Consideration received	Concept (Monetary)	For Period	Credit	ifrs-full:ConsiderationPaidReceived
1036	Increases due to interest accrued and expensed during the period	Concept (Monetary)	For Period	Credit	tac:IncreaseDecreaseDueToInterestAccruedAndExpensedDuringPeriodContractLiabilities
1037	Amounts transferred to payables	Concept (Monetary)	For Period	Credit	tac:TransfersToPayablesContractLiabilities
1038	Dec. 31, 2018	Concept (Monetary)	As Of	Credit	ifrs-full:ContractLiabilities
1039	2413402 - Disclosure - Expenses by Nature - Expenses Classified by Nature (Details)	Network	*	*	http://www.transalta.com/role/ExpensesByNatureExpensesClassifiedByNatureDetails
1040	Disclosure of products and services [table]	Table	*	*	ifrs-full:DisclosureOfProductsAndServicesTable
1041	Products and services [axis]	Axis			ifrs-full:ProductsAndServicesAxis
1042	Products and services [member]	Member			ifrs-full:ProductsAndServicesMember
1043	Fuel and purchased power	Member			tac:FuelAndPurchasedPowerMember
1044	Operations, maintenance and administration	Member			tac:OperationsMaintenanceAndAdministrationMember
1045	Disclosure of products and services [line items]	LineItems			ifrs-full:DisclosureOfProductsAndServicesLineItems
1046	Fuel(1)	Concept (Monetary)	For Period	Debit	ifrs-full:FuelExpense
1047	Coal inventory writedown (recovery)	Concept (Monetary)	For Period	Debit	ifrs-full:WritedownsReversalsOfInventories
1048	Purchased power	Concept (Monetary)	For Period	Debit	ifrs-full:CostOfPurchasedEnergySold
1049	Mine depreciation	Concept (Monetary)	For Period	Debit	ifrs-full:DepreciationExpense
1050	Salaries and benefits(1)	Concept (Monetary)	For Period	Debit	ifrs-full:EmployeeBenefitsExpense
1051	Other operating expenses	Concept (Monetary)	For Period	Debit	ifrs-full:OtherExpenseByNature
1052	Total	Concept (Monetary)	For Period	Debit	ifrs-full:CostOfSales
1053	Total	Concept (Monetary)	For Period	Debit	tac:OperationsMaintenanceAndAdministrativeExpense
1054	Adjustments for increase (decrease) in employee benefit liabilities	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForIncreaseDecreaseInEmployeeBenefitLiabilities
1055	2415401 - Disclosure - Asset Impairment Charges and Reversals (Details)	Network	*	*	http://www.transalta.com/role/AssetImpairmentChargesAndReversalsDetails
1056	Disclosure of impairment loss recognised or reversed [table]	Table	*	*	ifrs-full:DisclosureOfImpairmentLossRecognisedOrReversedTable
1057	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
1058	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
1059	Property, plant, and equipment	Member			tac:PropertyPlantsAndEquipmentMember
1060	Intangible assets	Member			ifrs-full:OtherPropertyPlantAndEquipmentMember
1061	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
1062	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
1063	Sundance Unit 2	Member			tac:SundanceUnit2Member
1064	Lakeswind	Member			tac:LakeswindMember
1065	Sundance Unit 1	Member			tac:SundanceUnit1Member
1066	Wintering Hills	Member			tac:WinteringHillsMember
1067	Segments [axis]	Axis			ifrs-full:SegmentsAxis
1068	Segments [member]	Member			ifrs-full:SegmentsMember
1069	Wind and Solar	Member			tac:WindandSolarMember
1070	Disclosure of impairment loss recognised or reversed [line items]	LineItems			ifrs-full:DisclosureOfImpairmentLossRecognisedOrReversedLineItems
1071	Impairment loss	Concept (Monetary)	For Period	Debit	ifrs-full:ImpairmentLoss
1072	Discount rate	Concept (Percent)	As Of		tac:DiscountRate
1073	Equity participation percentage	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInSubsidiary
1074	Cash transferred	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromSalesOfInvestmentProperty
1075	Decrease through classified as held for sale, investment property	Concept (Monetary)	For Period	Credit	ifrs-full:DecreaseThroughClassifiedAsHeldForSaleInvestmentProperty
1076	Write-downs (reversals of write-downs) of property, plant and equipment	Concept (Monetary)	For Period		ifrs-full:WritedownsReversalsOfPropertyPlantAndEquipment
1077	2416402 - Disclosure - Finance Lease Receivables (Details)	Network	*	*	http://www.transalta.com/role/FinanceLeaseReceivablesDetails
1078	Disclosure of recognised finance lease as assets by lessee [table]	Table	*	*	ifrs-full:DisclosureOfRecognisedFinanceLeaseAsAssetsByLesseeTable
1079	Maturity [axis]	Axis			ifrs-full:MaturityAxis
1080	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
1081	Within one year	Member			ifrs-full:NotLaterThanOneYearMember
1082	Second to fifth years inclusive	Member			ifrs-full:LaterThanTwoYearsAndNotLaterThanFiveYearsMember
1083	More than five years	Member			ifrs-full:LaterThanFiveYearsMember
1084	Disclosure of recognised finance lease as assets by lessee [line items]	LineItems			ifrs-full:DisclosureOfRecognisedFinanceLeaseAsAssetsByLesseeLineItems
1085	Minimum lease payments	Concept (Monetary)	As Of	Debit	ifrs-full:ExpectedFutureMinimumSubleasePaymentsReceivableUnderNoncancellableSubleasesClassifiedFinanceLease
1086	Present value of minimum lease payments	Concept (Monetary)	As Of	Debit	ifrs-full:MinimumFinanceLeasePaymentsReceivableAtPresentValue
1087	Less: unearned finance lease income	Concept (Monetary)	As Of	Credit	ifrs-full:UnearnedFinanceIncomeRelatingToFinanceLeasePaymentsReceivable
1088	Less: unearned finance lease income, present value	Concept (Monetary)	As Of	Credit	tac:Unearnedfinanceincomerelatingtofinanceleasepaymentsreceivablepresentvalue
1089	Add: unguaranteed residual value	Concept (Monetary)	As Of	Debit	ifrs-full:DiscountedUnguaranteedResidualValueOfAssetsSubjectToFinanceLease
1090	Add: unguaranteed residual value, present value	Concept (Monetary)	As Of	Debit	tac:Discountedunguaranteedresidualvalueofassetssubjecttofinanceleasepresentvalue
1091	Total finance lease receivables	Concept (Monetary)	As Of	Debit	ifrs-full:FinanceLeaseReceivables
1092	(Note 13)	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentFinanceLeaseReceivables
1093	Long-term portion of finance lease receivable (Note 8)	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentFinanceLeaseReceivables
1094	2416403 - Disclosure - Finance Lease Receivables Narrative (Details)	Network	*	*	http://www.transalta.com/role/FinanceLeaseReceivablesNarrativeDetails
1095	Disclosure of detailed information about business combination [table]	Table	*	*	ifrs-full:DisclosureOfBusinessCombinationsTable
1096	Transactions recognised separately from acquisition of assets and assumption of liabilities in business combination [axis]	Axis			ifrs-full:TransactionsRecognisedSeparatelyFromAcquisitionOfAssetsAndAssumptionOfLiabilitiesInBusinessCombinationAxis
1097	Transactions recognised separately from acquisition of assets and assumption of liabilities in business combination [member]	Member			ifrs-full:TransactionsRecognisedSeparatelyFromAcquisitionOfAssetsAndAssumptionOfLiabilitiesInBusinessCombinationMember
1098	Solomon Power Station	Member			tac:SolomonPowerStationMember
1099	Disclosure of detailed information about business combination [line items]	LineItems			ifrs-full:DisclosureOfBusinessCombinationsLineItems
1100	Total consideration transferred	Concept (Monetary)	As Of	Credit	ifrs-full:AcquisitiondateFairValueOfTotalConsiderationTransferred
1101	Consideration received	Concept (Monetary)	For Period	Credit	ifrs-full:ConsiderationPaidReceived
1102	2419402 - Disclosure - Net Other Operating (Income) Losses Analysis of income and expenses (Details)	Network	*	*	http://www.transalta.com/role/NetOtherOperatingIncomeLossesAnalysisOfIncomeAndExpensesDetails
1103	Analysis of income and expenses [Table]	Table	*	*	tac:AnalysisofincomeandexpensesTable
1104	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
1105	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
1106	California	Member			stpr:CA
1107	Analysis of income and expenses [Line Items]	LineItems			tac:AnalysisofincomeandexpensesLineItems
1108	Alberta Off-Coal Agreement	Concept (Monetary)	For Period	Credit	tac:GainsLossesonContractAgreement
1109	Termination of the Sundance B and C PPAs	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnDisposalsOfInvestments
1110	Mississauga cogeneration facility NUG Contract	Concept (Monetary)	For Period	Credit	tac:GainsLossesonContractRestructuring
1111	Insurance recoveries	Concept (Monetary)	For Period	Credit	ifrs-full:IncomeFromReimbursementsUnderInsurancePolicies
1112	Restructuring provision	Concept (Monetary)	For Period	Debit	ifrs-full:ExpenseOfRestructuringActivities
1113	Net other operating expense (income)	Concept (Monetary)	For Period	Credit	ifrs-full:OtherOperatingIncomeExpense
1114	2419403 - Disclosure - Net Other Operating (Income) Losses (Details)	Network	*	*	http://www.transalta.com/role/NetOtherOperatingIncomeLossesDetails
1115	Disclosure of types of insurance contracts [table]	Table	*	*	ifrs-full:DisclosureOfTypesOfInsuranceContractsTable
1116	Types of contracts [axis]	Axis			ifrs-full:TypesOfContractsAxis
1117	Types of contracts [member]	Member			ifrs-full:TypesOfContractsMember
1118	Mississauga Cogeneration Facility Contract [Member]	Member			tac:MississaugaCogenerationFacilityContractMember
1119	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
1120	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
1121	Wyoming Wind [Member]	Member			tac:WyomingWindMember
1122	Segment consolidation items [axis]	Axis			ifrs-full:SegmentConsolidationItemsAxis
1123	Entity's total for segment consolidation items [member]	Member			ifrs-full:EntitysTotalForSegmentConsolidationItemsMember
1124	Canadian Coal	Member			tac:CanadianCoalMember
1125	Segments [axis]	Axis			ifrs-full:SegmentsAxis
1126	Segments [member]	Member			ifrs-full:SegmentsMember
1127	Wind Generation	Member			tac:WindGenerationMember
1128	Coal generation	Member			tac:CoalGenerationMember
1129	Hydro	Member			tac:HydroGenerationMember
1130	Types of insurance contracts [axis]	Axis			ifrs-full:TypesOfInsuranceContractsAxis
1131	Types of insurance contracts [member]	Member			ifrs-full:InsuranceContractsMember
1132	Equipment Repair [Member]	Member			tac:EquipmentRepairMember
1133	Business interruption [member]	Member			tac:BusinessinterruptionMember
1134	Replacement and Refurbishment [Member]	Member			tac:ReplacementandRefurbishmentMember
1135	Disclosure of types of insurance contracts [line items]	LineItems			ifrs-full:DisclosureOfTypesOfInsuranceContractsLineItems
1136	Alberta off-coal agreement, annual cash payments, gross	Concept (Monetary)	For Period	Credit	tac:GainsLossesonContractAgreement
1137	Alberta off-coal agreement, annual cash payments, net	Concept (Monetary)	For Period	Credit	tac:GainsLossesonContractAgreementNet
1138	Gains (losses) on disposals of investments	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnDisposalsOfInvestments
1139	Mississauga cogeneration facility NUG Contract	Concept (Monetary)	For Period	Credit	tac:GainsLossesonContractRestructuring
1140	Discounted revenue	Concept (Monetary)	For Period	Debit	tac:Discountedrevenue
1141	Contract expenses and termination charges	Concept (Monetary)	For Period	Debit	tac:Contractexpensesandterminationcharges
1142	Accelerated depreciation	Concept (Monetary)	For Period	Debit	tac:Accelerateddepreciation
1143	Cash flow hedge unrealized gains (losses) from AOCI recognized in profit or loss	Concept (Monetary)	For Period	Credit	tac:CashFlowHedgeUnrealizedGainsLossesFromAOCIRecognizedinProfitorLoss
1144	Insurance recoveries	Concept (Monetary)	For Period	Credit	ifrs-full:IncomeFromReimbursementsUnderInsurancePolicies
1145	2420402 - Disclosure - Net Interest Expense (Details)	Network	*	*	http://www.transalta.com/role/NetInterestExpenseDetails
1146	Analysis of income and expenses [Table]	Table	*	*	tac:AnalysisofincomeandexpensesTable
1147	New IFRSs [axis]	Axis			ifrs-full:NewIFRSsAxis
1148	New IFRSs [member]	Member			ifrs-full:NewIFRSsMember
1149	IFRS 15	Member			ifrs-full:IncreaseDecreaseDueToApplicationOfIFRS15Member
1150	Classes of financial assets [axis]	Axis			ifrs-full:ClassesOfFinancialAssetsAxis
1151	Financial assets, class [member]	Member			ifrs-full:FinancialAssetsMember
1152	Project level financing that is no longer practicable	Member			tac:ProjectLevelFinancingThatIsNoLongerPracticableMember
1153	Analysis of income and expenses [Line Items]	LineItems			tac:AnalysisofincomeandexpensesLineItems
1154	Interest on debt	Concept (Monetary)	For Period		ifrs-full:InterestCostsIncurred
1155	Interest income	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromInterest
1156	Capitalized interest (Note 17)	Concept (Monetary)	For Period		ifrs-full:InterestCostsCapitalised
1157	Loss on redemption of bonds (Note 22)	Concept (Monetary)	For Period	Credit	ifrs-full:GainLossArisingFromDifferenceBetweenCarryingAmountOfFinancialLiabilityExtinguishedAndConsiderationPaid
1158	Interest on finance lease obligations	Concept (Monetary)	For Period	Debit	ifrs-full:InterestExpenseOnFinanceLeases
1159	Credit facility fees, bank charges and other interest	Concept (Monetary)	For Period	Debit	ifrs-full:InterestExpenseOnOtherFinancialLiabilities
1160	Keephills 1 outage interest (reversals) (Note 4(P))	Concept (Monetary)	For Period	Debit	tac:Interestaccrualsreversals
1161	Other	Concept (Monetary)	For Period	Debit	tac:OtherInterestExpense
1162	Accretion of provisions (Note 21)	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughTimeValueOfMoneyAdjustmentOtherProvisions
1163	Net interest expense	Concept (Monetary)	For Period	Debit	ifrs-full:InterestExpense
1164	2422402 - Disclosure - Income Taxes - Rate Reconciliations (Details)	Network	*	*	http://www.transalta.com/role/IncomeTaxesRateReconciliationsDetails
1165	Implied Table	Table	*	*	implied:Table
1166	Income Taxes [Abstract]	Abstract			tac:IncomeTaxesAbstract
1167	Earnings before income taxes	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossBeforeTax
1168	Net earnings attributable to non-controlling interests not subject to tax	Concept (Monetary)	For Period	Credit	tac:TaxEffectOfProfitLossAttributableToNonControllingInterestNotSubjectToTax
1169	Adjusted earnings before income taxes	Concept (Monetary)	For Period	Credit	tac:ProfitLossBeforeTaxAdjustedForNonTaxableIncomeNoncontrollingInterest
1170	Statutory Canadian federal and provincial income tax rate	Concept (Percent)	For Period		ifrs-full:ApplicableTaxRate
1171	Expected income tax expense (recovery)	Concept (Monetary)	For Period	Debit	ifrs-full:TaxExpenseIncomeAtApplicableTaxRate
1172	Increase (decrease) in income taxes resulting from:	Abstract			ifrs-full:ReconciliationOfAccountingProfitMultipliedByApplicableTaxRatesAbstract
1173	Lower effective foreign tax rates	Concept (Monetary)	For Period	Debit	ifrs-full:TaxEffectOfForeignTaxRates
1174	Deferred income tax expense related to temporary difference on investment in subsidiary	Concept (Monetary)	For Period	Debit	tac:TaxEffectOfDeferredIncomeTaxExpenseRelatedToInvestmentInSubsidiary
1175	MSA settlement	Concept (Monetary)	For Period	Debit	tac:TaxEffectOfLegalSettlement
1176	Writedown (reversal of writedown) of deferred income tax assets	Concept (Monetary)	For Period	Debit	ifrs-full:DeferredTaxExpenseArisingFromWritedownOrReversalOfWritedownOfDeferredTaxAsset
1177	Statutory and other rate differences	Concept (Monetary)	For Period	Debit	ifrs-full:TaxEffectFromChangeInTaxRate
1178	Resolution of uncertain tax matters	Concept (Monetary)	For Period	Debit	tac:TaxEffectOfResolutionOfUncertainTaxPositions
1179	Divestiture of investment	Concept (Monetary)	For Period	Debit	tac:TaxEffectOfDivestitureOfInvestment
1180	Other	Concept (Monetary)	For Period	Debit	ifrs-full:OtherTaxEffectsForReconciliationBetweenAccountingProfitAndTaxExpenseIncome
1181	Income tax expense (recovery)	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
1182	Effective tax rate	Concept (Percent)	For Period		ifrs-full:AverageEffectiveTaxRate
1183	2422403 - Disclosure - Income Taxes - Components of Income Tax Expense (Details)	Network	*	*	http://www.transalta.com/role/IncomeTaxesComponentsOfIncomeTaxExpenseDetails
1184	Disposal Groups, Including Discontinued Operations [Table]	Table	*	*	tac:DisposalGroupsIncludingDiscontinuedOperationsTable
1185	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
1186	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
1187	New Richmond	Member			tac:NewRichmondWindL.P.Member
1188	Continuing and discontinued operations [axis]	Axis			ifrs-full:ContinuingAndDiscontinuedOperationsAxis
1189	Discontinued operations [member]	Member			ifrs-full:DiscontinuedOperationsMember
1190	Solomon Power Station	Member			tac:SolomonPowerStationMember
1191	Canadian Assets	Member			tac:SarniaCogenerationPlantLeNordaisWindFarmAndRaggedChuteHydroFacilityCanadianAssetsMember
1192	Australian Assets	Member			tac:AustralianAssetsMember
1193	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
1194	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
1195	New Brunswick	Member			stpr:A3
1196	Alberta	Member			stpr:A0
1197	Disposal Groups, Including Discontinued Operations [Line Items]	LineItems			tac:DisposalGroupsIncludingDiscontinuedOperationsLineItems
1198	Current income tax expense(1)	Concept (Monetary)	For Period	Debit	ifrs-full:CurrentTaxExpenseIncomeAndAdjustmentsForCurrentTaxOfPriorPeriods
1199	Adjustments in respect of current income tax of previous years	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForCurrentTaxOfPriorPeriod
1200	Adjustments in respect of deferred income tax of previous years	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDeferredTaxOfPriorPeriods
1201	Deferred income tax expense (recovery) related to the origination and reversal of temporary differences	Concept (Monetary)	For Period	Debit	ifrs-full:DeferredTaxExpenseIncomeRelatingToOriginationAndReversalOfTemporaryDifferences
1202	Deferred income tax expense related to temporary difference on investment in subsidiary	Concept (Monetary)	For Period	Debit	tac:DeferredTaxExpenseIncomeRelatingToTemporaryDifferencesOnInvestmentInSubsidiary
1203	Deferred income tax expense resulting from changes in tax rates or laws	Concept (Monetary)	For Period	Debit	ifrs-full:DeferredTaxExpenseIncomeRelatingToTaxRateChangesOrImpositionOfNewTaxes
1204	Writedown (reversal of writedown) of deferred income tax assets	Concept (Monetary)	For Period	Debit	ifrs-full:DeferredTaxExpenseArisingFromWritedownOrReversalOfWritedownOfDeferredTaxAsset
1205	Income tax expense (recovery)	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
1206	Current income tax expense	Concept (Monetary)	For Period	Debit	ifrs-full:CurrentTaxExpenseIncome
1207	Deferred income tax expense (recovery)	Concept (Monetary)	For Period	Debit	ifrs-full:DeferredTaxExpenseIncome
1208	Deferred income tax liabilities (Note 11)	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredTaxLiabilities
1209	Net deferred tax assets	Concept (Monetary)	As Of	Debit	ifrs-full:NetDeferredTaxAssets
1210	Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Deferred Tax Asset, Income Tax Expense (Benefit)	Concept (Monetary)	For Period	Debit	tac:TaxCutsandJobsActof2017ChangeinTaxRateDeferredTaxAssetIncomeTaxExpenseBenefit
1211	Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Deferred Tax Liability, Income Tax (Expense) Benefit	Concept (Monetary)	For Period	Credit	tac:TaxCutsandJobsActof2017ChangeinTaxRateDeferredTaxLiabilityIncomeTaxExpenseBenefit
1212	Deferred tax expense (income) recognised in profit or loss	Concept (Monetary)	For Period		ifrs-full:DeferredTaxExpenseIncomeRecognisedInProfitOrLoss
1213	Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Deferred Tax Recovery	Concept (Monetary)	For Period	Debit	tac:TaxCutsandJobsActof2017ChangeinTaxRateDeferredTaxRecovery
1214	Corporate tax rate	Concept (Percent)	For Period		ifrs-full:ApplicableTaxRate
1215	2422404 - Disclosure - Income Taxes - Aggregate Current and Deferred Income Tax Charged to Equity (Details)	Network	*	*	http://www.transalta.com/role/IncomeTaxesAggregateCurrentAndDeferredIncomeTaxChargedToEquityDetails
1216	Implied Table	Table	*	*	implied:Table
1217	Income Taxes [Abstract]	Abstract			tac:IncomeTaxesAbstract
1218	Net impact related to cash flow hedges	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxRelatingToCashFlowHedgesOfOtherComprehensiveIncome
1219	Net impact related to net investment hedges	Concept (Monetary)	For Period	Debit	tac:Incometaxrelatingtohedgesofinvestmentsinequityinstruments
1220	Net actuarial gains (losses)	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxRelatingToRemeasurementsOfDefinedBenefitPlansOfOtherComprehensiveIncome
1221	Share issuance costs	Concept (Monetary)	For Period	Debit	tac:Incometaxrelatingtoshareissuancecostsofothercomprehensiveincome
1222	Loss on sale of investment in subsidiary	Concept (Monetary)	For Period	Debit	tac:Incometaxrelatingtogainslossesonsaleofinvestmentinsubsidiaryinothercomprehensiveincome
1223	Income tax expense reported in equity	Concept (Monetary)	For Period	Debit	ifrs-full:CurrentAndDeferredTaxRelatingToItemsChargedOrCreditedDirectlyToEquity
1224	2422405 - Disclosure - Income Taxes - Significant Components of Deferred Income Tax Assets (Liabilities) (Details)	Network	*	*	http://www.transalta.com/role/IncomeTaxesSignificantComponentsOfDeferredIncomeTaxAssetsLiabilitiesDetails
1225	Disclosure of temporary difference, unused tax losses and unused tax credits [table]	Table	*	*	ifrs-full:DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsTable
1226	Carrying amount, accumulated depreciation, amortisation and impairment and gross carrying amount [axis]	Axis			ifrs-full:CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis
1227	Carrying amount [member]	Member			ifrs-full:CarryingAmountMember
1228	Gross carrying amount	Member			ifrs-full:GrossCarryingAmountMember
1229	Accumulated impairment	Member			ifrs-full:AccumulatedImpairmentMember
1230	Temporary difference, unused tax losses and unused tax credits [axis]	Axis			ifrs-full:TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis
1231	Temporary difference, unused tax losses and unused tax credits [member]	Member			ifrs-full:TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsMember
1232	Net operating loss carryforwards	Member			ifrs-full:UnusedTaxLossesMember
1233	Future decommissioning and restoration costs	Member			tac:DecommissioningRestorationAndRehabilitationCostsRelatedTemporaryDifferencesMember
1234	Property, plant and equipment	Member			tac:PropertyPlantAndEquipmentRelatedTemporaryDifferencesMember
1235	Risk management assets and liabilities, net	Member			tac:NetRiskManagementAssetsAndLiabilitiesTemporaryDifferencesMember
1236	Employee future benefits and compensation plans	Member			tac:EmployeeBenefitsAndCompensationPlansTemporaryDifferencesMember
1237	Interest deductible in future periods	Member			tac:InterestDeductibleInFuturePeriodsTemporaryDifferencesMember
1238	Foreign exchange differences on US-denominated debt	Member			tac:ForeignExchangeTemporaryDifferencesMember
1239	Deferred coal revenues	Member			tac:DeferredRevenuesTemporaryDifferencesMember
1240	Other deductible temporary differences	Member			ifrs-full:OtherTemporaryDifferencesMember
1241	Disclosure of temporary difference, unused tax losses and unused tax credits [line items]	LineItems			ifrs-full:DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems
1242	Deferred tax liability (asset)	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredTaxLiabilityAsset
1243	Writedown of deferred income tax assets	Concept (Monetary)	As Of	Debit	ifrs-full:DeferredTaxAssets
1244	Net deferred tax liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NetDeferredTaxLiabilities
1245	2422406 - Disclosure - Income Taxes - Deferred Income Tax Liability Presentation (Details)	Network	*	*	http://www.transalta.com/role/IncomeTaxesDeferredIncomeTaxLiabilityPresentationDetails
1246	Implied Table	Table	*	*	implied:Table
1247	Income Taxes [Abstract]	Abstract			tac:IncomeTaxesAbstract
1248	Deferred income tax assets (Note 11)	Concept (Monetary)	As Of	Debit	ifrs-full:DeferredTaxAssets
1249	Deferred tax liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredTaxLiabilities
1250	Net deferred tax liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NetDeferredTaxLiabilities
1251	2422407 - Disclosure - Income Taxes - Contingencies (Details)	Network	*	*	http://www.transalta.com/role/IncomeTaxesContingenciesDetails
1252	Disclosure of contingent liabilities [table]	Table	*	*	ifrs-full:DisclosureOfContingentLiabilitiesTable
1253	Classes of contingent liabilities [axis]	Axis			ifrs-full:ClassesOfContingentLiabilitiesAxis
1254	Contingent liabilities [member]	Member			ifrs-full:ContingentLiabilitiesMember
1255	Uncertain tax positions	Member			ifrs-full:TaxContingentLiabilityMember
1256	Disclosure of contingent liabilities [line items]	LineItems			ifrs-full:DisclosureOfContingentLiabilitiesLineItems
1257	Provision for uncertain tax positions	Concept (Monetary)	As Of	Credit	ifrs-full:Provisions
1258	2425402 - Disclosure - Non-Controlling Interests - Subsidiaries and Operations with Non-Controlling Interests (Details)	Network	*	*	http://www.transalta.com/role/NonControllingInterestsSubsidiariesAndOperationsWithNonControllingInterestsDetails
1259	Disclosure of subsidiaries [table]	Table	*	*	ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesTable
1260	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
1261	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
1262	Kent Hills 3 Wind Project	Member			tac:KentHills3WindProjectMember
1263	Counterparties [axis]	Axis			ifrs-full:CounterpartiesAxis
1264	Counterparties [member]	Member			ifrs-full:CounterpartiesMember
1265	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
1266	Classes of ordinary shares [axis]	Axis			ifrs-full:ClassesOfOrdinarySharesAxis
1267	Common shares	Member			ifrs-full:OrdinarySharesMember
1268	Class B shares	Member			tac:ClassBsharesMember
1269	Common shares	Member			tac:CommonsharesMember
1270	Business combinations [axis]	Axis			ifrs-full:BusinessCombinationsAxis
1271	Entity's total for business combinations [member]	Member			ifrs-full:EntitysTotalForBusinessCombinationsMember
1272	Australian Assets	Member			tac:AustralianAssetsMember
1273	Legal Entity [Axis]	Axis			dei:LegalEntityAxis
1274	Entity [Domain]	Member			dei:EntityDomain
1275	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
1276	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
1277	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
1278	TransAlta Cogeneration L.P.	Member			tac:TransAltaCogenerationL.P.Member
1279	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
1280	Kent Hills wind farm	Member			tac:KentHillsWindFarmMember
1281	Coal facility	Member			tac:CoalFacilityMember
1282	Disclosure of subsidiaries [line items]	LineItems			ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesLineItems
1283	Proportion of ownership interests held by non-controlling interests	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestsHeldByNoncontrollingInterests
1284	Increase in contractual power capacity (in megawatts)	Concept (num:powerItemType)	For Period		tac:IncreaseDecreaseinContractualPowerCapacityPower
1285	Capacity of facility (in megawatts)	Concept (num:powerItemType)	As Of		tac:CapacityOfPowerGenerationAssetsPower
1286	Increase (decrease) through conversion of convertible instruments, equity	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughConversionOfConvertibleInstruments
1287	Issue of convertible instruments	Concept (Monetary)	For Period	Credit	ifrs-full:IssueOfConvertibleInstruments
1288	Proportion of equity participation in subsidiary	Concept (Percent)	For Period		tac:ProportionOfEquityParticipationInSubsidiary
1289	Shares offered for conversion	Concept (Shares)	As Of		tac:Sharesofferedforconversion
1290	Equity securities received upon conversion of shares	Concept (Shares)	As Of		tac:Equitysecuritiesreceiveduponconversionofshares
1291	2425403 - Disclosure - Non-Controlling Interests - Share of Ownership and Equity Participation in TransAlta Renewables (Details)	Network	*	*	http://www.transalta.com/role/NonControllingInterestsShareOfOwnershipAndEquityParticipationInTransaltaRenewablesDetails
1292	Disclosure of subsidiaries [table]	Table	*	*	ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesTable
1293	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
1294	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
1295	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
1296	Disclosure of subsidiaries [line items]	LineItems			ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesLineItems
1297	Equity participation percentage	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInSubsidiary
1298	Proportion of equity participation in subsidiary	Concept (Percent)	For Period		tac:ProportionOfEquityParticipationInSubsidiary
1299	2425404 - Disclosure - Non-Controlling Interests - Earnings of Subsidiaries with Non-Controlling Interests (Details)	Network	*	*	http://www.transalta.com/role/NonControllingInterestsEarningsOfSubsidiariesWithNonControllingInterestsDetails
1300	Disclosure of subsidiaries [table]	Table	*	*	ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesTable
1301	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
1302	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
1303	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
1304	TransAlta Cogeneration L.P.	Member			tac:TransAltaCogenerationL.P.Member
1305	Disclosure of subsidiaries [line items]	LineItems			ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesLineItems
1306	Revenues	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
1307	Net earnings (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
1308	Total comprehensive income	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncome
1309	Amounts attributable to the non-controlling interests:	Abstract			ifrs-full:ComprehensiveIncomeAttributableToAbstract
1310	Net earnings	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossAttributableToNoncontrollingInterests
1311	Total comprehensive income	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncomeAttributableToNoncontrollingInterests
1312	Distributions paid to non-controlling interests	Concept (Monetary)	For Period	Credit	ifrs-full:DividendsPaidToNoncontrollingInterests
1313	2425405 - Disclosure - Non-Controlling Interests - Financial Position of Non-Controlling Interests (Details)	Network	*	*	http://www.transalta.com/role/NonControllingInterestsFinancialPositionOfNonControllingInterestsDetails
1314	Disclosure of subsidiaries [table]	Table	*	*	ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesTable
1315	Legal Entity [Axis]	Axis			dei:LegalEntityAxis
1316	Entity [Domain]	Member			dei:EntityDomain
1317	TransAlta Cogeneration L.P.	Member			tac:TransAltaCogenerationL.P.Member
1318	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
1319	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
1320	Coal facility	Member			tac:CoalFacilityMember
1321	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
1322	TransAlta Cogeneration L.P.	Member			tac:TransAltaCogenerationL.P.Member
1323	Disclosure of subsidiaries [line items]	LineItems			ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesLineItems
1324	Current assets	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentAssets
1325	Long-term assets	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentAssets
1326	Current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentLiabilities
1327	Long-term liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentLiabilities
1328	Total equity	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
1329	Non-controlling interests (Note 12)	Concept (Monetary)	As Of	Credit	ifrs-full:NoncontrollingInterests
1330	Ownership and voting rights percentage	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestsHeldByNoncontrollingInterests
1331	2428402 - Disclosure - Trade and Other Receivables (Details)	Network	*	*	http://www.transalta.com/role/TradeAndOtherReceivablesDetails
1332	Implied Table	Table	*	*	implied:Table
1333	Subclassifications of assets, liabilities and equities [abstract]	Abstract			ifrs-full:SubclassificationsOfAssetsLiabilitiesAndEquitiesAbstract
1334	Trade accounts receivable	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentTradeReceivables
1335	Mississauga recontracting receivable	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentReceivablesFromContractsWithCustomers
1336	Net trade receivables	Concept (Monetary)	As Of	Debit	ifrs-full:TradeReceivables
1337	Promissory note receivable	Concept (Monetary)	As Of	Debit	ifrs-full:OtherCurrentReceivables
1338	Collateral paid (Note 15)	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentNoncashAssetsPledgedAsCollateralForWhichTransfereeHasRightByContractOrCustomToSellOrRepledgeCollateral
1339	Current portion of finance lease receivables (Note 8)	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentFinanceLeaseReceivables
1340	Current portion of loan receivable (Note 20)	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentLoansAndReceivables
1341	Income taxes receivables	Concept (Monetary)	As Of	Debit	tac:CurrentReceivablesFromIncomeTaxes
1342	Trade and other receivables	Concept (Monetary)	As Of	Debit	ifrs-full:TradeAndOtherCurrentReceivables
1343	2431402 - Disclosure - Financial Instruments Carrying amounts and classifications of financial assets and liabilities (Details)	Network	*	*	http://www.transalta.com/role/FinancialInstrumentsCarryingAmountsAndClassificationsOfFinancialAssetsAndLiabilitiesDetails
1344	Disclosure of financial assets and liabilities [Table]	Table	*	*	tac:DisclosureoffinancialassetsandliabilitiesTable
1345	Classes of financial assets [axis]	Axis			ifrs-full:ClassesOfFinancialAssetsAxis
1346	Financial assets, class [member]	Member			ifrs-full:FinancialAssetsMember
1347	Cash and cash equivalents	Member			tac:CashAndCashEquivalents1Member
1348	Restricted cash	Member			tac:RestrictedCashMember
1349	Trade and other receivables	Member			tac:TradeAndOtherReceivablesMember
1350	Long-term portion of finance lease receivables	Member			tac:LongtermPortionOfFinanceLeaseReceivablesMember
1351	Risk management assets	Member			tac:RiskManagementAssetsMember
1352	Other assets	Member			ifrs-full:OtherAssetsMember
1353	Categories of financial assets [axis]	Axis			ifrs-full:CategoriesOfFinancialAssetsAxis
1354	Financial assets, category [member]	Member			ifrs-full:FinancialAssetsCategoryMember
1355	Hedging Asset	Member			tac:HedgingAssetMember
1356	Trading securities	Member			ifrs-full:TradingSecuritiesMember
1357	Amortized cost	Member			ifrs-full:FinancialAssetsAtAmortisedCostCategoryMember
1358	Other financial assets (FVTPL)	Member			tac:FinancialAssetsOtherCategoryMember
1359	Loans and receivables	Member			ifrs-full:LoansAndReceivablesCategoryMember
1360	Maturity [axis]	Axis			ifrs-full:MaturityAxis
1361	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
1362	Within one year	Member			ifrs-full:NotLaterThanOneYearMember
1363	Later than one year	Member			ifrs-full:LaterThanOneYearMember
1364	Classes of financial instruments [axis]	Axis			ifrs-full:ClassesOfFinancialInstrumentsAxis
1365	Financial instruments, class [member]	Member			ifrs-full:ClassesOfFinancialInstrumentsMember
1366	Derivatives	Member			ifrs-full:DerivativesMember
1367	Classes of financial liabilities [axis]	Axis			ifrs-full:ClassesOfFinancialLiabilitiesAxis
1368	Financial liabilities, class [member]	Member			ifrs-full:FinancialLiabilitiesMember
1369	Accounts payable and accrued liabilities	Member			tac:AccountsPayableAndAccruedLiabilities1Member
1370	Dividends payable	Member			tac:DividendsPayable1Member
1371	Risk management liabilities	Member			tac:RiskManagementLiabilitiesMember
1372	Credit facilities, long-term debt and finance lease obligations(2)	Member			tac:CreditFacilitiesLongtermDebtAndFinanceLeaseObligations1Member
1373	Categories of financial liabilities [axis]	Axis			ifrs-full:CategoriesOfFinancialLiabilitiesAxis
1374	Financial liabilities, category [member]	Member			ifrs-full:FinancialLiabilitiesCategoryMember
1375	Financial liabilities at amortised cost, category [member]	Member			ifrs-full:FinancialLiabilitiesAtAmortisedCostCategoryMember
1376	Trading securities	Member			ifrs-full:TradingSecuritiesMember
1377	Other financial liabilities	Member			tac:OtherFinancialLiabilitiesMember
1378	Hedging Liabilities	Member			tac:HedgingLiabilitiesMember
1379	Carrying amount, accumulated depreciation, amortisation and impairment and gross carrying amount [axis]	Axis			ifrs-full:CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis
1380	Carrying amount [member]	Member			ifrs-full:CarryingAmountMember
1381	Gross carrying amount	Member			ifrs-full:GrossCarryingAmountMember
1382	Past due status [axis]	Axis			ifrs-full:PastDueStatusAxis
1383	Past due status [member]	Member			ifrs-full:PastDueStatusMember
1384	Current	Member			ifrs-full:CurrentMember
1385	Long-term	Member			tac:Longterm1Member
1386	Disclosure of detailed information about financial instruments [line items]	LineItems			ifrs-full:DisclosureOfFinancialInstrumentsLineItems
1387	Cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashEquivalents
1388	Financial assets	Concept (Monetary)	As Of	Debit	ifrs-full:FinancialAssets
1389	Financial liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:FinancialLiabilities
1390	2431403 - Disclosure - Financial Instruments Sensitivity ranges for the base fair values (Details)	Network	*	*	http://www.transalta.com/role/FinancialInstrumentsSensitivityRangesForBaseFairValuesDetails
1391	Disclosure of sensitivity analysis for actuarial assumptions [table]	Table	*	*	ifrs-full:DisclosureOfSensitivityAnalysisForActuarialAssumptionsTable
1392	Range [axis]	Axis			ifrs-full:RangeAxis
1393	Ranges [member]	Member			ifrs-full:RangesMember
1394	Maximum	Member			ifrs-full:TopOfRangeMember
1395	Minimum	Member			ifrs-full:BottomOfRangeMember
1396	Types of contracts [axis]	Axis			ifrs-full:TypesOfContractsAxis
1397	Types of contracts [member]	Member			ifrs-full:TypesOfContractsMember
1398	Long-Term Power Sale - U.S.	Member			tac:LongTermPowerSaleU.S.Member
1399	Long-Term Power Sale - Alberta	Member			tac:LongTermPowerSaleAlbertaMember
1400	Unit Contingent Power Purchases	Member			tac:UnitContingentPowerPurchasesMember
1401	Structured Products - Eastern U.S.	Member			tac:StructuredProductsEasternU.S.Member
1402	Long-Term Wind Energy Sale - Eastern U.S.	Member			tac:LongTermWindEnergySaleEasternU.S.Member
1403	Others	Member			tac:OthersMember
1404	Contract duration [axis]	Axis			ifrs-full:ContractDurationAxis
1405	Contract duration [member]	Member			ifrs-full:ContractDurationMember
1406	Long-term contracts	Member			ifrs-full:LongtermContractsMember
1407	Disclosure of sensitivity analysis for actuarial assumptions [line items]	LineItems			ifrs-full:DisclosureOfSensitivityAnalysisForActuarialAssumptionsLineItems
1408	Base fair value	Concept (Monetary)	As Of		ifrs-full:NotionalAmount
1409	Sensitivity ranges for the base fair value, reasonably possible change in risk assumption, financial instruments	Concept (Integer)	For Period		tac:SensitivityRangesForTheBaseFairValueReasonablyPossibleIncreaseDecreaseInRiskAssumptionFinancialInstruments
1410	2431404 - Disclosure - Financial Instruments (Details)	Network	*	*	http://www.transalta.com/role/FinancialInstrumentsDetails
1411	Disclosure of detailed information about financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfFinancialInstrumentsTable
1412	Measurement [axis]	Axis			ifrs-full:MeasurementAxis
1413	At fair value [member]	Member			ifrs-full:AtFairValueMember
1414	Recurring fair value measurement	Member			ifrs-full:RecurringFairValueMeasurementMember
1415	Levels of fair value hierarchy [axis]	Axis			ifrs-full:LevelsOfFairValueHierarchyAxis
1416	All levels of fair value hierarchy [member]	Member			ifrs-full:AllLevelsOfFairValueHierarchyMember
1417	Level I	Member			ifrs-full:Level1OfFairValueHierarchyMember
1418	Level III	Member			ifrs-full:Level3OfFairValueHierarchyMember
1419	Contract duration [axis]	Axis			ifrs-full:ContractDurationAxis
1420	Contract duration [member]	Member			ifrs-full:ContractDurationMember
1421	Long-term contracts	Member			ifrs-full:LongtermContractsMember
1422	Plan Name [Axis]	Axis			tac:PlanName1Axis
1423	Plan Name [Domain]	Member			tac:PlanName1Domain
1424	UNITED STATES	Member			country:US
1425	Canada	Member			country:CA
1426	Types of contracts [axis]	Axis			ifrs-full:TypesOfContractsAxis
1427	Types of contracts [member]	Member			ifrs-full:TypesOfContractsMember
1428	Fixed-price contracts	Member			ifrs-full:FixedpriceContractsMember
1429	Long-Term Power Sale - Alberta	Member			tac:LongTermPowerSaleAlbertaMember
1430	Unit Contingent Power Purchases	Member			tac:UnitContingentPowerPurchasesMember
1431	Structured Products - Eastern U.S.	Member			tac:StructuredProductsEasternU.S.Member
1432	Forward contract	Member			ifrs-full:ForwardContractMember
1433	Long-Term Wind Energy Sale - Eastern U.S.	Member			tac:LongTermWindEnergySaleEasternU.S.Member
1434	Range [axis]	Axis			ifrs-full:RangeAxis
1435	Ranges [member]	Member			ifrs-full:RangesMember
1436	Minimum	Member			ifrs-full:BottomOfRangeMember
1437	Maximum	Member			ifrs-full:TopOfRangeMember
1438	Disclosure of detailed information about financial instruments [line items]	LineItems			ifrs-full:DisclosureOfFinancialInstrumentsLineItems
1439	Long-term fixed price power sale contract, delivery volume	Concept (num:powerItemType)	As Of		tac:LongtermFixedPricePowerSaleContractDeliveryVolume
1440	Risk management assets (Note 14 and 15)	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentDerivativeFinancialAssets
1441	Forward power price ranges per MWh	Concept (Monetary)	As Of	Credit	tac:DerivativeForwardPrice1
1442	Increase (decrease) in derivative forward power prices, reasonable possible	Concept (Monetary)	For Period	Debit	tac:IncreaseDecreaseinDerivativeForwardPowerPricesReasonablyPossible
1443	Decrease in base fair value	Concept (Monetary)	For Period	Credit	tac:IncreaseDecreaseInBaseFairValue
1444	Decrease in sensitivity values	Concept (Monetary)	For Period	Credit	tac:SensitivityAnalysisForBaseFairValueReasonablyPossibleChangeInFairValueImpactOnPreTaxEarnings
1445	Sensitivity analysis in derivative, forward price, percent	Concept (Percent)	For Period		tac:SensitivityAnalysisInDerivativeForwardPricePercent
1446	Price discount ranges, percent	Concept (Percent)	For Period		tac:IncreaseDecreaseInDerivativePriceDiscountPercent
1447	Volume discount ranges, percent	Concept (Percent)	For Period		tac:IncreaseDecreaseInDerivativeVolumeDiscountPercent
1448	Sensitivity analysis in derivative, price discount, percent	Concept (Percent)	For Period		tac:SensitivityAnalysisInDerivativePriceDiscountPercent
1449	Sensitivity analysis in derivative, volume discount ranges, percent	Concept (Percent)	For Period		tac:SensitivityAnalysisInDerivativeVolumeDiscountPercent
1450	Basis relationship, percent	Concept (Percent)	For Period		tac:IncreaseDecreaseInDerivativeBasisRelationshipPercent
1451	Non-standard shape factors, percent	Concept (Percent)	For Period		tac:IncreaseDecreaseInDerivativeNonStandardShapeFactorsPercent
1452	Sensitivity analysis in derivative, basis relationship, percent	Concept (Percent)	For Period		tac:SensitivityAnalysisInDerivativeBasisRelationshipPercent
1453	Sensitivity analysis in derivative, non-standard shape factors, percent	Concept (Percent)	For Period		tac:SensitivityAnalysisInDerivativeNonStandardShapeFactorsPercent
1454	Implied volatility for shares, significant unobservable inputs, entity's own derivative	Concept (Percent)	For Period		tac:ImpliedVolatilityForSharesSignificantUnobservableInputsEntitysOwnDerivative
1455	Implied correlations for shares, significant unobservable inputs, entity's own derivative	Concept (Percent)	For Period		tac:ImpliedCorrelationsForSharesSignificantUnobservableInputsEntitysOwnDerivative
1456	Sensitivity Analysis In Derivative, Implied Volatility, Percent	Concept (Percent)	For Period		tac:SensitivityAnalysisInDerivativeImpliedVolatilityPercent
1457	Sensitivity Analysis In Derivative, Implied Correlations, Percent	Concept (Percent)	For Period		tac:SensitivityAnalysisInDerivativeImpliedCorrelationsPercent
1458	Sensitivity Analysis In Derivative, Implied Volatility And Correlation, Percent	Concept (Percent)	For Period		tac:SensitivityAnalysisInDerivativeImpliedVolatilityAndCorrelationPercent
1459	Risk exposure associated with instruments sharing characteristic	Concept (Monetary)	As Of		ifrs-full:RiskExposureAssociatedWithInstrumentsSharingCharacteristic
1460	2431405 - Disclosure - Financial Instruments Fair value of the commodity risk management assets and liabilities by classification level (Details)	Network	*	*	http://www.transalta.com/role/FinancialInstrumentsFairValueOfCommodityRiskManagementAssetsAndLiabilitiesByClassificationLevelDetails
1461	Disclosure of risk management strategy related to hedge accounting [table]	Table	*	*	ifrs-full:DisclosureOfRiskManagementStrategyRelatedToHedgeAccountingTable
1462	Types of financial assets [axis]	Axis			ifrs-full:TypesOfFinancialAssetsAxis
1463	Financial assets, type [member]	Member			ifrs-full:FinancialAssetsTypeMember
1464	Derivative Instruments, Existing Contracts [Member]	Member			tac:DerivativeInstrumentsExistingContractsMember
1465	Derivative Instruments, New Contracts [Member]	Member			tac:DerivativeInstrumentsNewContractsMember
1466	Derivative Instruments, Contracts Settled [Member]	Member			tac:DerivativeInstrumentsContractsSettledMember
1467	Classes of financial instruments [axis]	Axis			ifrs-full:ClassesOfFinancialInstrumentsAxis
1468	Financial instruments, class [member]	Member			ifrs-full:ClassesOfFinancialInstrumentsMember
1469	Derivatives	Member			ifrs-full:DerivativesMember
1470	Types of hedges [axis]	Axis			ifrs-full:TypesOfHedgesAxis
1471	Hedges [member]	Member			ifrs-full:TypesOfHedgesMember
1472	Fair value hedges [member]	Member			ifrs-full:FairValueHedgesMember
1473	Non-Hedges	Member			tac:NonHedgesMember
1474	Measurement [axis]	Axis			ifrs-full:MeasurementAxis
1475	At fair value [member]	Member			ifrs-full:AtFairValueMember
1476	Recurring fair value measurement	Member			ifrs-full:RecurringFairValueMeasurementMember
1477	Non-recurring fair value measurement [member]	Member			ifrs-full:NonrecurringFairValueMeasurementMember
1478	Levels of fair value hierarchy [axis]	Axis			ifrs-full:LevelsOfFairValueHierarchyAxis
1479	All levels of fair value hierarchy [member]	Member			ifrs-full:AllLevelsOfFairValueHierarchyMember
1480	Level I	Member			ifrs-full:Level1OfFairValueHierarchyMember
1481	Level 2 of fair value hierarchy [member]	Member			ifrs-full:Level2OfFairValueHierarchyMember
1482	Level III	Member			ifrs-full:Level3OfFairValueHierarchyMember
1483	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1484	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1485	Other	Member			tac:OtherRiskMember
1486	Commodity risk management	Member			ifrs-full:CommodityPriceRiskMember
1487	Disclosure of risk management strategy related to hedge accounting [line items]	LineItems			ifrs-full:DisclosureOfRiskManagementStrategyRelatedToHedgeAccountingLineItems
1488	Risk exposure associated with instruments sharing characteristic	Concept (Monetary)	As Of		ifrs-full:RiskExposureAssociatedWithInstrumentsSharingCharacteristic
1489	Market price changes	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseInExposureToCreditRiskOnLoanCommitmentsAndFinancialGuaranteeContracts
1490	Change in foreign exchange rates	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnExchangeDifferencesOnTranslationRecognisedInProfitOrLoss
1491	Transfers into Level 3 of fair value hierarchy, assets	Concept (Monetary)	For Period	Debit	ifrs-full:TransfersIntoLevel3OfFairValueHierarchyAssets
1492	Discontinued hedge accounting on certain contracts (see Note 4)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossFromDiscontinuedOperations
1493	Gains recognized in OCI	Concept (Monetary)	For Period	Credit	ifrs-full:GainLossOnHedgeIneffectivenessRecognisedInOtherComprehensiveIncome
1494	Total gains included in earnings before income taxes	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnCashFlowHedgesBeforeTax
1495	Unrealized gains included in earnings before income taxes relating to met assets held	Concept (Monetary)	For Period	Credit	tac:UnrealizedGainsLossesOnHedgeInstrumentsBeforeTax
1496	2431406 - Disclosure - Financial Instruments Fair value of financial assets and liabilities measured at other than fair value (Details)	Network	*	*	http://www.transalta.com/role/FinancialInstrumentsFairValueOfFinancialAssetsAndLiabilitiesMeasuredAtOtherThanFairValueDetails
1497	Disclosure of fair value measurement of liabilities [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfLiabilitiesTable
1498	Measurement [axis]	Axis			ifrs-full:MeasurementAxis
1499	At fair value [member]	Member			ifrs-full:AtFairValueMember
1500	Recurring fair value measurement	Member			ifrs-full:RecurringFairValueMeasurementMember
1501	Levels of fair value hierarchy [axis]	Axis			ifrs-full:LevelsOfFairValueHierarchyAxis
1502	All levels of fair value hierarchy [member]	Member			ifrs-full:AllLevelsOfFairValueHierarchyMember
1503	Level 2 of fair value hierarchy [member]	Member			ifrs-full:Level2OfFairValueHierarchyMember
1504	Classes of financial liabilities [axis]	Axis			ifrs-full:ClassesOfFinancialLiabilitiesAxis
1505	Financial liabilities, class [member]	Member			ifrs-full:FinancialLiabilitiesMember
1506	Long-term Debt1 [Member]	Member			tac:LongtermDebt1Member
1507	Categories of financial liabilities [axis]	Axis			ifrs-full:CategoriesOfFinancialLiabilitiesAxis
1508	Financial liabilities, category [member]	Member			ifrs-full:FinancialLiabilitiesCategoryMember
1509	Financial liabilities at fair value through profit or loss, category [member]	Member			ifrs-full:FinancialLiabilitiesAtFairValueThroughProfitOrLossCategoryMember
1510	Disclosure of fair value measurement of liabilities [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfLiabilitiesLineItems
1511	Financial liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:FinancialLiabilities
1512	2431407 - Disclosure - Financial Instruments Inception Gains And Losses (Details)	Network	*	*	http://www.transalta.com/role/FinancialInstrumentsInceptionGainsAndLossesDetails
1513	Implied Table	Table	*	*	implied:Table
1514	Disclosure of detailed information about financial instruments [abstract]	Abstract			ifrs-full:DisclosureOfFinancialInstrumentsAbstract
1515	Changes in aggregate difference between fair value at initial recognition and transaction price yet to be recognised in profit or loss [abstract]	Abstract			ifrs-full:ChangesInAggregateDifferenceBetweenFairValueAtInitialRecognitionAndAmountDeterminedUsingValuationTechniqueYetToBeRecognisedAbstract
1516	Unamortized net gain at beginning of year	Concept (Monetary)	As Of		ifrs-full:AggregateDifferenceBetweenFairValueAtInitialRecognitionAndAmountDeterminedUsingValuationTechniqueYetToBeRecognised
1517	New inception gains (losses)	Concept (Monetary)	For Period		ifrs-full:IncreaseDecreaseThroughNewTransactionsAggregateDifferenceBetweenFairValueAtInitialRecognitionAndAmountDeterminedUsingValuationTechniqueYetToBeRecognised
1518	Change in foreign exchange rates	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughForeignExchangeFinancialAssets
1519	Amortization recorded in net earnings during the year	Concept (Monetary)	For Period		ifrs-full:IncreaseDecreaseInAggregateDifferenceBetweenFairValueAtInitialRecognitionAndAmountDeterminedUsingValuationTechniqueYetToBeRecognised
1520	Unamortized net gain at end of year	Concept (Monetary)	As Of		ifrs-full:AggregateDifferenceBetweenFairValueAtInitialRecognitionAndAmountDeterminedUsingValuationTechniqueYetToBeRecognised
1521	2437402 - Disclosure - Risk Management Activities - Net Risk Management Assets and Liabilities (Details)	Network	*	*	http://www.transalta.com/role/RiskManagementActivitiesNetRiskManagementAssetsAndLiabilitiesDetails
1522	Disclosure of detailed information about financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfFinancialInstrumentsTable
1523	Hedging instruments [axis]	Axis			ifrs-full:HedgingInstrumentsAxis
1524	Hedging instruments [member]	Member			ifrs-full:HedgingInstrumentsMember
1525	Long-term debt	Member			tac:Borrowings1Member
1526	Types of hedges [axis]	Axis			ifrs-full:TypesOfHedgesAxis
1527	Hedges [member]	Member			ifrs-full:TypesOfHedgesMember
1528	Discontinued Cash Flow Hedge Position	Member			tac:DiscontinuedCashFlowHedgePositionMember
1529	Net investment hedges	Member			ifrs-full:HedgesOfNetInvestmentInForeignOperationsMember
1530	Cash flow hedges	Member			ifrs-full:CashFlowHedgesMember
1531	Fair value hedges	Member			ifrs-full:FairValueHedgesMember
1532	Discontinued Hedge Positions	Member			tac:DiscontinuedHedgePositionsMember
1533	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1534	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1535	Interest rate risk	Member			ifrs-full:InterestRateRiskMember
1536	Commodity risk management	Member			ifrs-full:CommodityPriceRiskMember
1537	Other	Member			tac:OtherRiskMember
1538	Hedging Designation [Axis]	Axis			tac:HedgingDesignation1Axis
1539	Hedging Designation [Member]	Member			tac:HedgingDesignation1Member
1540	Designated as a hedge	Member			tac:HedgingInstruments1Member
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1542	Classes of assets [axis]	Axis			ifrs-full:ClassesOfAssetsAxis
1543	Assets [member]	Member			ifrs-full:ClassesOfAssetsMember
1544	Financial Assets	Member			tac:FinancialAssets1Member
1545	Current	Member			tac:CurrentFinancialAssetsMember
1546	Long-term	Member			tac:NoncurrentFinancialAssetsMember
1547	Classes of liabilities [axis]	Axis			ifrs-full:ClassesOfLiabilitiesAxis
1548	Liabilities [member]	Member			ifrs-full:LiabilitiesMember
1549	Financial Liabilities	Member			tac:FinancialLiabilities1Member
1550	Current	Member			tac:CurrentFinancialLiabilitiesMember
1551	Long-term	Member			tac:NoncurrentFinancialLiabilitiesMember
1552	Disclosure of detailed information about financial instruments [line items]	LineItems			ifrs-full:DisclosureOfFinancialInstrumentsLineItems
1553	Derivative hedge, notional amount	Concept (Monetary)	As Of		invest:DerivativeNotionalAmount
1554	Risk exposure associated with instruments sharing characteristic	Concept (Monetary)	As Of		ifrs-full:RiskExposureAssociatedWithInstrumentsSharingCharacteristic
1555	2437403 - Disclosure - Risk Management Activities - Netting Arrangements (Details)	Network	*	*	http://www.transalta.com/role/RiskManagementActivitiesNettingArrangementsDetails
1556	Disclosure of detailed information about financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfFinancialInstrumentsTable
1557	Classes of assets [axis]	Axis			ifrs-full:ClassesOfAssetsAxis
1558	Assets [member]	Member			ifrs-full:ClassesOfAssetsMember
1559	Current financial assets	Member			tac:CurrentFinancialAssetsMember
1560	Long-term financial assets	Member			tac:NoncurrentFinancialAssetsMember
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1562	Liabilities [member]	Member			ifrs-full:LiabilitiesMember
1563	Current financial liabilities	Member			tac:CurrentFinancialLiabilitiesMember
1564	Long-term financial liabilities	Member			tac:NoncurrentFinancialLiabilitiesMember
1565	Disclosure of detailed information about financial instruments [line items]	LineItems			ifrs-full:DisclosureOfFinancialInstrumentsLineItems
1566	Gross financial assets subject to offsetting, enforceable master netting arrangements or similar agreements	Concept (Monetary)	As Of	Debit	ifrs-full:GrossFinancialAssetsSubjectToOffsettingEnforceableMasterNettingArrangementsOrSimilarAgreements
1567	Gross financial liabilities subject to offsetting, enforceable master netting arrangements or similar agreements	Concept (Monetary)	As Of	Credit	ifrs-full:GrossFinancialLiabilitiesSubjectToOffsettingEnforceableMasterNettingArrangementsOrSimilarAgreements
1568	Gross financial liabilities set off against financial assets subject to offsetting, enforceable master netting arrangements or similar agreements	Concept (Monetary)	As Of	Credit	ifrs-full:GrossFinancialLiabilitiesSetOffAgainstFinancialAssetsSubjectToOffsettingEnforceableMasterNettingArrangementsOrSimilarAgreements
1569	Gross financial assets set off against financial liabilities subject to offsetting, enforceable master netting arrangements or similar agreements	Concept (Monetary)	As Of	Debit	ifrs-full:GrossFinancialAssetsSetOffAgainstFinancialLiabilitiesSubjectToOffsettingEnforceableMasterNettingArrangementsOrSimilarAgreements
1570	Net financial assets subject to offsetting, enforceable master netting arrangements or similar agreements in statement of financial position	Concept (Monetary)	As Of	Debit	ifrs-full:NetFinancialAssetsSubjectToOffsettingEnforceableMasterNettingArrangementsOrSimilarAgreementsInStatementOfFinancialPosition
1571	Net financial liabilities subject to offsetting, enforceable master netting arrangements or similar agreements in statement of financial position	Concept (Monetary)	As Of	Credit	ifrs-full:NetFinancialLiabilitiesSubjectToOffsettingEnforceableMasterNettingArrangementsOrSimilarAgreementsInStatementOfFinancialPosition
1572	2437404 - Disclosure - Risk Management Activities - Hedging Instruments (Details)	Network	*	*	http://www.transalta.com/role/RiskManagementActivitiesHedgingInstrumentsDetails
1573	Disclosure of detailed information about financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfFinancialInstrumentsTable
1574	Components of equity [axis]	Axis			ifrs-full:ComponentsOfEquityAxis
1575	Equity [member]	Member			ifrs-full:EquityMember
1576	Reserve of exchange differences on translation	Member			ifrs-full:ReserveOfExchangeDifferencesOnTranslationMember
1577	Currency1 [Axis]	Axis			tac:Currency1Axis
1578	Currency1 [Domain]	Member			tac:Currency1Domain
1579	U.S. Dollars	Member			currency:USD
1580	Australia, Dollars	Member			currency:AUD
1581	Range [axis]	Axis			ifrs-full:RangeAxis
1582	Ranges [member]	Member			ifrs-full:RangesMember
1583	Minimum	Member			ifrs-full:BottomOfRangeMember
1584	Maximum	Member			ifrs-full:TopOfRangeMember
1585	Maturity [axis]	Axis			ifrs-full:MaturityAxis
1586	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
1587	2019	Member			ifrs-full:LaterThanOneYearAndNotLaterThanTwoYearsMember
1588	2018	Member			ifrs-full:NotLaterThanOneYearMember
1589	Hedging instruments [axis]	Axis			ifrs-full:HedgingInstrumentsAxis
1590	Hedging instruments [member]	Member			ifrs-full:HedgingInstrumentsMember
1591	Electricity	Member			tac:ElectricityMember
1592	Long-term debt	Member			tac:Borrowings1Member
1593	Physical power sales	Member			tac:PhysicalPowerSalesMember
1594	Foreign Currency Forward Contracts	Member			ifrs-full:ForwardContractMember
1595	Foreign Exchange Forward Contracts - foreign-denominated receipts/expenditures CAD 1	Member			tac:ForeignExchangeForwardContractsForeignDenominatedReceiptsExpendituresCAD1Member
1596	Foreign Exchange Forward Contracts - foreign-denominated receipts/expenditures CAD 2	Member			tac:ForeignExchangeForwardContractsForeignDenominatedReceiptsExpendituresCAD2Member
1597	Foreign Exchange Forward Contracts - foreign-denominated receipts/expenditures	Member			tac:ForeignExchangeForwardContractsForeignDenominatedReceiptsExpendituresMember
1598	Foreign Exchange Forward Contracts - foreign-denominated debt	Member			tac:ForeignExchangeForwardContractsForeignDenominatedDebtMember
1599	Cross-Currency Swaps - foreign-denominated debt	Member			ifrs-full:CurrencySwapContractMember
1600	Cross-Currency Swaps - foreign-denominated debt 2	Member			tac:CurrencySwapContract2Member
1601	Natural gas	Member			tac:NaturalGasMember
1602	Transmission	Member			tac:TransmissionMember
1603	Emissions	Member			tac:EmissionsMember
1604	Heating Oil	Member			tac:HeatingOil1Member
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1606	Types of hedges [axis]	Axis			ifrs-full:TypesOfHedgesAxis
1607	Hedges [member]	Member			ifrs-full:TypesOfHedgesMember
1608	Discontinued Hedge Positions	Member			tac:DiscontinuedHedgePositionsMember
1609	Discontinued Cash Flow Hedge Position	Member			tac:DiscontinuedCashFlowHedgePositionMember
1610	Non-Hedges	Member			tac:NonHedgesMember
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1612	Cash flow hedges	Member			ifrs-full:CashFlowHedgesMember
1613	Fair value hedges	Member			ifrs-full:FairValueHedgesMember
1614	Net Investment Hedge	Member			tac:NetInvestmentHedgeMember
1615	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1616	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1617	Commodity risk management	Member			ifrs-full:CommodityPriceRiskMember
1618	Currency risk	Member			ifrs-full:CurrencyRiskMember
1619	Interest rate risk	Member			ifrs-full:InterestRateRiskMember
1620	Disclosure of detailed information about financial instruments [line items]	LineItems			ifrs-full:DisclosureOfFinancialInstrumentsLineItems
1621	Derivative hedge, notional amount	Concept (Monetary)	As Of		invest:DerivativeNotionalAmount
1622	Collateral paid (Note 15)	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentNoncashAssetsPledgedAsCollateralForWhichTransfereeHasRightByContractOrCustomToSellOrRepledgeCollateral
1623	Interest rate	Concept (Percent)	As Of		ifrs-full:BorrowingsInterestRate
1624	Notional amount	Concept (Monetary)	As Of		ifrs-full:NotionalAmount
1625	Notional amount sold	Concept (Monetary)	As Of	Debit	tac:DerivativeNotionalAmountSold
1626	Notional amount purchased	Concept (Monetary)	As Of	Debit	tac:DerivativeNotionalAmountPurchased
1627	Fair value asset	Concept (Monetary)	As Of	Debit	ifrs-full:HedgingInstrumentAssets
1628	Fair value liability	Concept (Monetary)	As Of	Credit	ifrs-full:HedgingInstrumentLiabilities
1629	Notional amount sold	Concept (num:energyItemType)	As Of		tac:DerivativeNonmonetaryNotionalAmountSold
1630	Notional amount purchased	Concept (num:energyItemType)	As Of		tac:DerivativeNonmonetaryNotionalAmountPurchased
1631	Unrealized pre-tax gains (losses)	Concept (Monetary)	For Period	Credit	tac:Unrealizedpretaxgainslosses
1632	Cumulative gains (loss) in derivative instruments	Concept (Monetary)	For Period	Credit	tac:CumulativeGainsLossInDerivativeInstruments
1633	Borrowings subject to floating interest rates	Concept (Percent)	As Of		tac:BorrowingsSubjectToFloatingInterestRates
1634	Fair value hedge, cumulative gain (loss) amortized	Concept (Monetary)	For Period	Credit	tac:CumulativeGainsLossesOnDiscontinuedHedgedItem
1635	Gain (loss) on hedge ineffectiveness	Concept (Monetary)	For Period	Credit	ifrs-full:GainLossOnHedgeIneffectiveness
1636	Reserve of cash flow hedges	Concept (Monetary)	As Of	Credit	ifrs-full:ReserveOfCashFlowHedges
1637	Gains (losses) on exchange differences on translation, net of tax	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnExchangeDifferencesOnTranslationNetOfTax
1638	2437405 - Disclosure - Risk Management Activities - Effect on Cash Flow Hedges (Details)	Network	*	*	http://www.transalta.com/role/RiskManagementActivitiesEffectOnCashFlowHedgesDetails
1639	Disclosure of detailed information about financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfFinancialInstrumentsTable
1640	Scenario1 [Axis]	Axis			tac:Scenario1Axis
1641	Scenario1 [Domain]	Member			tac:Scenario1Domain
1642	Scenario, Forecast	Member			tac:ScenarioForecast1Member
1643	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
1644	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
1645	Mississauga Congeneration Facility [Member]	Member			tac:MississaugaCongenerationFacilityMember
1646	Types of hedges [axis]	Axis			ifrs-full:TypesOfHedgesAxis
1647	Hedges [member]	Member			ifrs-full:TypesOfHedgesMember
1648	Fair value hedges	Member			ifrs-full:FairValueHedgesMember
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1651	Profit (Loss)	Member			tac:ProfitLoss1Member
1652	Fuel and purchased power	Member			tac:FuelAndPurchasedPowerMember
1653	Foreign exchange (gain) loss	Member			tac:ForeignExchangeLossMember
1654	Foreign exchange (gain) loss	Member			tac:ForeignExchangeGainMember
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1656	Balance Sheet Location [Axis]	Axis			tac:BalanceSheetLocation1Axis
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1659	Property, plant, and equipment	Member			tac:PropertyPlantsAndEquipmentMember
1660	Hedging instruments [axis]	Axis			ifrs-full:HedgingInstrumentsAxis
1661	Hedging instruments [member]	Member			ifrs-full:HedgingInstrumentsMember
1662	Interest Rate Contracts [Member]	Member			tac:InterestRateContractsMember
1663	Commodity contracts	Member			tac:CommodityContractsMember
1664	Foreign exchange forwards on commodity contracts	Member			tac:ForeignExchangeForwardsOnCommodityContractsMember
1665	Foreign exchange forwards on project hedges	Member			tac:ForeignExchangeForwardsOnProjectHedgesMember
1666	Foreign exchange forwards on US debt	Member			tac:ForeignExchangeForwardsOnU.S.DebtMember
1667	Cross-currency swaps	Member			tac:CrossCurrencySwapsMember
1668	Forward starting interest rate swaps	Member			tac:ForwardStartingInterestRateSwapsMember
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1672	Disclosure of detailed information about financial instruments [line items]	LineItems			ifrs-full:DisclosureOfFinancialInstrumentsLineItems
1673	Total gains included in earnings before income taxes	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnCashFlowHedgesBeforeTax
1674	Other comprehensive income that will be reclassified to profit or loss, net of tax	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeThatWillBeReclassifiedToProfitOrLossNetOfTax
1675	Gains (losses) on exchange differences on translation, before tax	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnExchangeDifferencesOnTranslationBeforeTax
1676	Gains (losses) on cash flow hedges, before tax	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnHedgingInstrument
1677	Gain (loss) on hedge ineffectiveness recognised in other comprehensive income	Concept (Monetary)	For Period	Credit	ifrs-full:GainLossOnHedgeIneffectivenessRecognisedInOtherComprehensiveIncome
1678	Gain (loss) on hedge ineffectiveness recognised in profit or loss	Concept (Monetary)	For Period	Credit	ifrs-full:GainLossOnHedgeIneffectivenessRecognisedInProfitOrLoss
1679	2437406 - Disclosure - Risk Management Activities - Non-Hedges (Details)	Network	*	*	http://www.transalta.com/role/RiskManagementActivitiesNonHedgesDetails
1680	Disclosure of nature and extent of risks arising from financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsTable
1681	Hedging instruments [axis]	Axis			ifrs-full:HedgingInstrumentsAxis
1682	Hedging instruments [member]	Member			ifrs-full:HedgingInstrumentsMember
1683	Electricity	Member			tac:ElectricityMember
1684	Natural gas	Member			tac:NaturalGasMember
1685	Transmission	Member			tac:TransmissionMember
1686	Emissions	Member			tac:EmissionsMember
1687	Types of hedges [axis]	Axis			ifrs-full:TypesOfHedgesAxis
1688	Hedges [member]	Member			ifrs-full:TypesOfHedgesMember
1689	Non-Hedges	Member			tac:NonHedgesMember
1690	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1691	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1692	Commodity risk management	Member			ifrs-full:CommodityPriceRiskMember
1693	Currency risk	Member			ifrs-full:CurrencyRiskMember
1694	Disclosure of nature and extent of risks arising from financial instruments [line items]	LineItems			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
1695	Notional amount sold	Concept (num:energyItemType)	As Of		tac:DerivativeNonmonetaryNotionalAmountSold
1696	Foreign exchange gain (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnExchangeDifferencesOnTranslationRecognisedInProfitOrLoss
1697	Notional amount purchased	Concept (num:energyItemType)	As Of		tac:DerivativeNonmonetaryNotionalAmountPurchased
1698	Derivative, Nonmonetary Notional Amount Sold, Emissions	Concept (num:massItemType)	As Of		tac:DerivativeNonmonetaryNotionalAmountSoldEmissions
1699	Derivative, Nonmonetary Notional Amount Purchased, Emissions	Concept (num:massItemType)	As Of		tac:DerivativeNonmonetaryNotionalAmountPurchasedEmissions
1700	2437407 - Disclosure - Risk Management Activities - Foreign Currency Rate Risk Management (Details)	Network	*	*	http://www.transalta.com/role/RiskManagementActivitiesForeignCurrencyRateRiskManagementDetails
1701	Implied Table	Table	*	*	implied:Table
1702	Financial Instruments [Abstract]	Abstract			tac:FinancialInstrumentsAbstract
1703	Derivative hedge, notional amount	Concept (Monetary)	As Of		invest:DerivativeNotionalAmount
1704	Gains (losses) on derivatives designated as cash flow hedges, net of tax	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnCashFlowHedgesNetOfTax
1705	2437408 - Disclosure - Risk Management Activities - Additional Information (Details)	Network	*	*	http://www.transalta.com/role/RiskManagementActivitiesAdditionalInformationDetails
1706	Disclosure of nature and extent of risks arising from financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsTable
1707	Classes of financial instruments [axis]	Axis			ifrs-full:ClassesOfFinancialInstrumentsAxis
1708	Financial instruments, class [member]	Member			ifrs-full:ClassesOfFinancialInstrumentsMember
1709	Letter of credit	Member			tac:LetterofCreditMember
1710	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1711	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1712	Commodity risk management	Member			ifrs-full:CommodityPriceRiskMember
1713	Commodity Price Risk - Proprietary Trading [Member]	Member			tac:CommodityPriceRiskProprietaryTradingMember
1714	Commodity Price Risk - Generation [Member]	Member			tac:CommodityPriceRiskGenerationMember
1715	Commodity Price Risk - Generation - Mark To Market Value [Member]	Member			tac:CommodityPriceRiskGenerationMarkToMarketValueMember
1716	Disclosure of nature and extent of risks arising from financial instruments [line items]	LineItems			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
1717	Collateral paid (Note 15)	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentNoncashAssetsPledgedAsCollateralForWhichTransfereeHasRightByContractOrCustomToSellOrRepledgeCollateral
1718	Financial assets pledged as collateral for liabilities or contingent liabilities	Concept (Monetary)	As Of	Debit	ifrs-full:FinancialAssetsPledgedAsCollateralForLiabilitiesOrContingentLiabilities
1719	Value at risk	Concept (Monetary)	As Of		ifrs-full:ValueAtRisk
1720	Collateral posted on derivative liabilities	Concept (Monetary)	As Of	Debit	tac:CollateralonDerivativeInstruments
1721	Derivative, contingent feature, additional collateral requirement	Concept (Monetary)	As Of	Debit	tac:DerivativeInstrumentContingentFeatureIncreaseinCollateralRequirement
1722	2437409 - Disclosure - Risk Management Activities - Interest Rate Risk (Details)	Network	*	*	http://www.transalta.com/role/RiskManagementActivitiesInterestRateRiskDetails
1723	Disclosure of nature and extent of risks arising from financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsTable
1724	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1725	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1726	Interest rate risk	Member			ifrs-full:InterestRateRiskMember
1727	Disclosure of nature and extent of risks arising from financial instruments [line items]	LineItems			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
1728	Sensitivity analysis, Net earnings increase (decrease)	Concept (Monetary)	For Period	Credit	tac:SensitivityAnalysisForTypesOfMarketRiskReasonablyPossibleChangeInRiskVariableImpactOnProfitLoss
1729	Sensitivity Analysis For Types Of Market Risk, Reasonably Possible Change In Risk Variable, Percent	Concept (Percent)	For Period		tac:SensitivityAnalysisForTypesOfMarketRiskReasonablyPossibleChangeInRiskVariablePercent
1730	Sensitivity analysis, OCI gain	Concept (Monetary)	For Period	Credit	tac:SensitivityAnalysisForTypesOfMarketRiskReasonablyPossibleChangeInRiskVariableImpactOnOtherComprehensiveIncome
1731	2437410 - Disclosure - Risk Management Activities - Sensitivity Analysis For Management Assessment (Details)	Network	*	*	http://www.transalta.com/role/RiskManagementActivitiesSensitivityAnalysisForManagementAssessmentDetails
1732	Disclosure of sensitivity analysis for actuarial assumptions [table]	Table	*	*	ifrs-full:DisclosureOfSensitivityAnalysisForActuarialAssumptionsTable
1733	Currency1 [Axis]	Axis			tac:Currency1Axis
1734	Currency1 [Domain]	Member			tac:Currency1Domain
1735	U.S. Dollars	Member			currency:USD
1736	Australia, Dollars	Member			currency:AUD
1737	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1738	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1739	Currency risk	Member			ifrs-full:CurrencyRiskMember
1740	Disclosure of sensitivity analysis for actuarial assumptions [line items]	LineItems			ifrs-full:DisclosureOfSensitivityAnalysisForActuarialAssumptionsLineItems
1741	Sensitivity analysis, Net earnings increase (decrease)	Concept (Monetary)	For Period	Credit	tac:SensitivityAnalysisForTypesOfMarketRiskReasonablyPossibleChangeInRiskVariableImpactOnProfitLoss
1742	Sensitivity analysis, OCI gain	Concept (Monetary)	For Period	Credit	tac:SensitivityAnalysisForTypesOfMarketRiskReasonablyPossibleChangeInRiskVariableImpactOnOtherComprehensiveIncome
1743	Sensitivity analysis, management assessment	Concept (Monetary)	For Period	Credit	tac:SensitivityAnalysisForTypesOfMarketRiskReasonablyPossibleChangeInRiskVariable
1744	2437411 - Disclosure - Risk Management Activities - Credit Risk (Details)	Network	*	*	http://www.transalta.com/role/RiskManagementActivitiesCreditRiskDetails
1745	Disclosure of credit risk exposure [table]	Table	*	*	ifrs-full:DisclosureOfCreditRiskExposureTable
1746	Classes of financial assets [axis]	Axis			ifrs-full:ClassesOfFinancialAssetsAxis
1747	Financial assets, class [member]	Member			ifrs-full:FinancialAssetsMember
1748	Trade and other receivables	Member			tac:TradeAndOtherReceivablesMember
1749	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1750	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1751	Credit risk	Member			ifrs-full:CreditRiskMember
1752	External credit grades [axis]	Axis			ifrs-full:ExternalCreditGradesAxis
1753	Entity's total for external credit grades [member]	Member			ifrs-full:EntitysTotalForExternalCreditGradesMember
1754	Investment Grade [Member]	Member			tac:InvestmentGradeMember
1755	Non-Investment Grade [Member]	Member			tac:NonInvestmentGradeMember
1756	Classes of financial instruments [axis]	Axis			ifrs-full:ClassesOfFinancialInstrumentsAxis
1757	Financial instruments, class [member]	Member			ifrs-full:ClassesOfFinancialInstrumentsMember
1758	Trade and other receivables	Member			tac:TradeAndOtherReceivablesMember
1759	Long-term portion of finance lease receivables	Member			tac:LongtermPortionOfFinanceLeaseReceivablesMember
1760	Risk management assets	Member			tac:RiskManagementAssetsMember
1761	Loans and receivables	Member			ifrs-full:LoansAndReceivablesCategoryMember
1762	Disclosure of credit risk exposure [line items]	LineItems			ifrs-full:DisclosureOfCreditRiskExposureLineItems
1763	Credit risk, allocation percentage	Concept (Percent)	As Of		tac:CreditRiskAllocationPercentage
1764	Maximum exposure to credit risk	Concept (Monetary)	As Of		ifrs-full:MaximumExposureToCreditRisk
1765	Trade and other receivables	Concept (Monetary)	As Of	Debit	ifrs-full:TradeAndOtherCurrentReceivables
1766	2437412 - Disclosure - Risk Management Activities - Maturity (Details)	Network	*	*	http://www.transalta.com/role/RiskManagementActivitiesMaturityDetails
1767	Disclosure of financial liabilities [table]	Table	*	*	ifrs-full:DisclosureOfFinancialLiabilitiesTable
1768	Types of hedges [axis]	Axis			ifrs-full:TypesOfHedgesAxis
1769	Hedges [member]	Member			ifrs-full:TypesOfHedgesMember
1770	Non-Hedges	Member			tac:NonHedgesMember
1771	Hedging instruments [axis]	Axis			ifrs-full:HedgingInstrumentsAxis
1772	Hedging instruments [member]	Member			ifrs-full:HedgingInstrumentsMember
1773	Electricity	Member			tac:ElectricityMember
1774	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1775	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1776	Commodity risk management	Member			ifrs-full:CommodityPriceRiskMember
1777	Carrying amount, accumulated depreciation, amortisation and impairment and gross carrying amount [axis]	Axis			ifrs-full:CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis
1778	Carrying amount [member]	Member			ifrs-full:CarryingAmountMember
1779	Gross carrying amount	Member			ifrs-full:GrossCarryingAmountMember
1780	Maturity [axis]	Axis			ifrs-full:MaturityAxis
1781	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
1782	Within one year	Member			ifrs-full:NotLaterThanOneYearMember
1783	2019	Member			ifrs-full:LaterThanOneYearAndNotLaterThanTwoYearsMember
1784	2020	Member			ifrs-full:LaterThanTwoYearsAndNotLaterThanThreeYearsMember
1785	2021	Member			ifrs-full:LaterThanThreeYearsAndNotLaterThanFourYearsMember
1786	2022	Member			ifrs-full:LaterThanFourYearsAndNotLaterThanFiveYearsMember
1787	More than five years	Member			ifrs-full:LaterThanFiveYearsMember
1788	Classes of financial liabilities [axis]	Axis			ifrs-full:ClassesOfFinancialLiabilitiesAxis
1789	Financial liabilities, class [member]	Member			ifrs-full:FinancialLiabilitiesMember
1790	Categories of financial liabilities [axis]	Axis			ifrs-full:CategoriesOfFinancialLiabilitiesAxis
1791	Financial liabilities, category [member]	Member			ifrs-full:FinancialLiabilitiesCategoryMember
1792	Disclosure of financial liabilities [line items]	LineItems			ifrs-full:DisclosureOfFinancialLiabilitiesLineItems
1793	Notional amount	Concept (Decimal)	As Of		invest:DerivativeNonmonetaryNotionalAmount
1794	Accounts payable and accrued liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:TradeAndOtherCurrentPayables
1795	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
1796	Derivative financial liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:DerivativeFinancialLiabilities
1797	Finance lease liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:FinanceLeaseLiabilities
1798	Interest income on debt instruments held	Concept (Monetary)	As Of	Credit	ifrs-full:InterestPayable
1799	Dividends payable (Note 24 and 25)	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentDividendPayables
1800	Liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:Liabilities
1801	Average Power Prices	Concept (Share)	As Of		tac:AveragePowerPrices
1802	2437413 - Disclosure - Risk Management Activities - Commodity Risk Management (Details)	Network	*	*	http://www.transalta.com/role/RiskManagementActivitiesCommodityRiskManagementDetails
1803	Disclosure of detailed information about hedges [table]	Table	*	*	ifrs-full:DisclosureOfHedgeAccountingTable
1804	Hedging instruments [axis]	Axis			ifrs-full:HedgingInstrumentsAxis
1805	Hedging instruments [member]	Member			ifrs-full:HedgingInstrumentsMember
1806	Electricity	Member			tac:ElectricityMember
1807	Natural gas	Member			tac:NaturalGasMember
1808	Transmission	Member			tac:TransmissionMember
1809	Emissions	Member			tac:EmissionsMember
1810	Heating Oil	Member			tac:HeatingOil1Member
1811	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1812	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1813	Commodity risk management	Member			ifrs-full:CommodityPriceRiskMember
1814	Types of hedges [axis]	Axis			ifrs-full:TypesOfHedgesAxis
1815	Hedges [member]	Member			ifrs-full:TypesOfHedgesMember
1816	Cash flow hedges	Member			ifrs-full:CashFlowHedgesMember
1817	Non-Hedges	Member			tac:NonHedgesMember
1818	Disclosure of detailed information about hedges [line items]	LineItems			ifrs-full:DisclosureOfHedgeAccountingLineItems
1819	Notional amount sold	Concept (num:energyItemType)	As Of		tac:DerivativeNonmonetaryNotionalAmountSold
1820	Notional amount purchased	Concept (num:energyItemType)	As Of		tac:DerivativeNonmonetaryNotionalAmountPurchased
1821	Derivative, Nonmonetary Notional Amount Sold, Emissions	Concept (num:massItemType)	As Of		tac:DerivativeNonmonetaryNotionalAmountSoldEmissions
1822	Derivative, Nonmonetary Notional Amount Purchased, Emissions	Concept (num:massItemType)	As Of		tac:DerivativeNonmonetaryNotionalAmountPurchasedEmissions
1823	Derivative, Nonmonetary Notional Amount Sold In Gallons	Concept (num:volumeItemType)	As Of		tac:DerivativeNonmonetaryNotionalAmountSoldInGallons
1824	Derivative, Nonmonetary Notional Amount Purchased In Gallons	Concept (num:volumeItemType)	As Of		tac:DerivativeNonmonetaryNotionalAmountPurchasedInGallons
1825	2440402 - Disclosure - Inventory Components of Inventory (Details)	Network	*	*	http://www.transalta.com/role/InventoryComponentsOfInventoryDetails
1826	Implied Table	Table	*	*	implied:Table
1827	Disclosure of inventories [Abstract]	Abstract			tac:DisclosureofinventoriesAbstract
1828	Parts and materials	Concept (Monetary)	As Of	Debit	ifrs-full:ProductionSupplies
1829	Coal	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentFuel
1830	Deferred stripping costs	Concept (Monetary)	As Of	Debit	tac:CurrentDeferredStrippingCosts
1831	Natural gas	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentNaturalGas
1832	Purchased emission credits	Concept (Monetary)	As Of	Debit	tac:CurrentPurchasedEmissionCredit
1833	Inventories	Concept (Monetary)	As Of	Debit	ifrs-full:Inventories
1834	2440403 - Disclosure - Inventory Change in Inventory (Details)	Network	*	*	http://www.transalta.com/role/InventoryChangeInInventoryDetails
1835	Implied Table	Table	*	*	implied:Table
1836	Disclosure of inventories [Abstract]	Abstract			tac:DisclosureofinventoriesAbstract
1837	Inventories at the beginning of the period	Concept (Monetary)	As Of	Debit	ifrs-full:Inventories
1838	Net addition	Concept (Monetary)	For Period	Debit	tac:AdditionsOtherThanThroughBusinessCombinationsInventory
1839	Writedowns	Concept (Monetary)	For Period	Debit	tac:AdditionsFromAcquisitionsInventory
1840	Reversal of writedowns	Concept (Monetary)	For Period		ifrs-full:InventoryWritedown2011
1841	Change in foreign exchange rates	Concept (Monetary)	For Period	Debit	tac:IncreaseDecreaseThroughNetExchangeDifferencesInventory
1842	Net addition	Concept (Monetary)	For Period	Credit	tac:InventoryUsed
1843	Reversal of writedowns	Concept (Monetary)	For Period		ifrs-full:ReversalOfInventoryWritedown
1844	Inventories at the end of the period	Concept (Monetary)	As Of	Debit	ifrs-full:Inventories
1845	2443402 - Disclosure - Property, Plant, and Equipment (Details)	Network	*	*	http://www.transalta.com/role/PropertyPlantAndEquipmentDetails
1846	Disclosure of detailed information about property, plant and equipment [table]	Table	*	*	ifrs-full:DisclosureOfPropertyPlantAndEquipmentTable
1847	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
1848	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
1849	Mining property and equipment	Member			ifrs-full:MiningPropertyMember
1850	Disclosure of detailed information about property, plant and equipment [line items]	LineItems			ifrs-full:DisclosureOfPropertyPlantAndEquipmentLineItems
1851	Interest costs capitalised	Concept (Monetary)	For Period		ifrs-full:InterestCostsCapitalised
1852	Capitalisation rate of borrowing costs eligible for capitalisation	Concept (Percent)	For Period		ifrs-full:CapitalisationRateOfBorrowingCostsEligibleForCapitalisation
1853	Assets under finance leases	Concept (Monetary)	As Of	Debit	ifrs-full:RecognisedFinanceLeaseAsAssets
1854	2443403 - Disclosure - Property, Plant, and Equipment - Reconciliation of the changes in the carrying amount of PP&E (Details)	Network	*	*	http://www.transalta.com/role/PropertyPlantAndEquipmentReconciliationOfChangesInCarryingAmountOfPpeDetails
1855	Disclosure of detailed information about property, plant and equipment [table]	Table	*	*	ifrs-full:DisclosureOfPropertyPlantAndEquipmentTable
1856	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
1857	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
1858	US Wind Projects - Big Level [Member]	Member			tac:USWindProjectsBigLevelMember
1859	Classes of financial instruments [axis]	Axis			ifrs-full:ClassesOfFinancialInstrumentsAxis
1860	Financial instruments, class [member]	Member			ifrs-full:ClassesOfFinancialInstrumentsMember
1861	Finance lease receivables	Member			ifrs-full:LeaseReceivablesMember
1862	Categories of financial assets [axis]	Axis			ifrs-full:CategoriesOfFinancialAssetsAxis
1863	Financial assets, category [member]	Member			ifrs-full:FinancialAssetsCategoryMember
1864	Finance Lease	Member			tac:FinanceLeaseMember
1865	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
1866	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
1867	Poplar Creek	Member			tac:PoplarCreekMember
1868	Wintering Hills	Member			tac:WinteringHillsMember
1869	Classes of other provisions [axis]	Axis			ifrs-full:ClassesOfProvisionsAxis
1870	Other provisions [member]	Member			ifrs-full:OtherProvisionsMember
1871	Decommissioning and restoration	Member			ifrs-full:ProvisionForDecommissioningRestorationAndRehabilitationCostsMember
1872	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
1873	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
1874	Land	Member			ifrs-full:LandMember
1875	Coal generation	Member			tac:CoalGenerationMember
1876	Gas generation	Member			tac:GasGenerationMember
1877	Renewable generation	Member			tac:RenewableGenerationMember
1878	Mining property and equipment	Member			ifrs-full:MiningPropertyMember
1879	Assets under construction	Member			ifrs-full:ConstructionInProgressMember
1880	Capital spares and other	Member			tac:CapitalSparesAndOtherMember
1881	Gas equipment	Member			tac:GasEquipmentMember
1882	Carrying amount, accumulated depreciation, amortisation and impairment and gross carrying amount [axis]	Axis			ifrs-full:CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis
1883	Carrying amount [member]	Member			ifrs-full:CarryingAmountMember
1884	Gross carrying amount	Member			ifrs-full:GrossCarryingAmountMember
1885	Accumulated depreciation	Member			ifrs-full:AccumulatedDepreciationAndAmortisationMember
1886	Disclosure of detailed information about property, plant and equipment [line items]	LineItems			ifrs-full:DisclosureOfPropertyPlantAndEquipmentLineItems
1887	Property, plant and equipment, beginning of the period	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
1888	Additions	Concept (Monetary)	For Period	Debit	ifrs-full:AdditionsOtherThanThroughBusinessCombinationsPropertyPlantAndEquipment
1889	Acquisitions	Concept (Monetary)	For Period	Debit	ifrs-full:AcquisitionsThroughBusinessCombinationsPropertyPlantAndEquipment
1890	Disposals	Concept (Monetary)	For Period	Credit	ifrs-full:DisposalsPropertyPlantAndEquipment
1891	Reclassification to held for sale (Note 4)	Concept (Monetary)	For Period	Credit	ifrs-full:DecreaseThroughClassifiedAsHeldForSalePropertyPlantAndEquipment
1892	Impairment reversals	Concept (Monetary)	For Period		ifrs-full:ReversalOfImpairmentLossRecognisedInProfitOrLossPropertyPlantAndEquipment
1893	Revisions and additions to decommissioning and restoration costs	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughOtherChangesPropertyPlantAndEquipment
1894	Retirement of assets	Concept (Monetary)	For Period	Credit	ifrs-full:RetirementsPropertyPlantAndEquipment
1895	Change in foreign exchange rates	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughNetExchangeDifferencesPropertyPlantAndEquipment
1896	Reclassification to held for sale	Concept (Monetary)	For Period	Debit	ifrs-full:ReclassificationIntoAvailableforsaleFinancialAssets
1897	Transfers(2)(3)	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughTransfersPropertyPlantAndEquipment
1898	Impairment charges	Concept (Monetary)	For Period		ifrs-full:ImpairmentLossRecognisedInProfitOrLossPropertyPlantAndEquipment
1899	Depreciation	Concept (Monetary)	For Period		ifrs-full:DepreciationPropertyPlantAndEquipment
1900	Property, plant and equipment, end of the period	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
1901	Current spare parts	Concept (Monetary)	As Of	Debit	ifrs-full:SpareParts
1902	2449402 - Disclosure - Goodwill (Details)	Network	*	*	http://www.transalta.com/role/GoodwillDetails
1903	Disclosure of detailed information about intangible assets [table]	Table	*	*	ifrs-full:DisclosureOfIntangibleAssetsTable
1904	Range [axis]	Axis			ifrs-full:RangeAxis
1905	Ranges [member]	Member			ifrs-full:RangesMember
1906	Minimum	Member			ifrs-full:BottomOfRangeMember
1907	Maximum	Member			ifrs-full:TopOfRangeMember
1908	Segments [axis]	Axis			ifrs-full:SegmentsAxis
1909	Segments [member]	Member			ifrs-full:SegmentsMember
1910	Hydro	Member			tac:HydroGenerationMember
1911	Wind and Solar	Member			tac:WindandSolarMember
1912	Energy Marketing	Member			tac:EnergyMarketingMember
1913	Disclosure of detailed information about intangible assets [line items]	LineItems			ifrs-full:DisclosureOfIntangibleAssetsLineItems
1914	Goodwill (Note 18)	Concept (Monetary)	As Of	Debit	ifrs-full:Goodwill
1915	Electricity prices	Concept (num:energyItemType)	For Period		tac:ElectricityPriceEnergy
1916	Discount rate used to calculate goodwill impairment	Concept (Percent)	As Of		ifrs-full:DiscountRateUsedInCurrentMeasurementOfFairValueLessCostsOfDisposal
1917	2458402 - Disclosure - Intangible Assets (Details)	Network	*	*	http://www.transalta.com/role/IntangibleAssetsDetails
1918	Disclosure of reconciliation of changes in intangible assets and goodwill [table]	Table	*	*	ifrs-full:DisclosureOfReconciliationOfChangesInIntangibleAssetsAndGoodwillTable
1919	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
1920	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
1921	US Wind Projects - Big Level [Member]	Member			tac:USWindProjectsBigLevelMember
1922	Lakeswind	Member			tac:LakeswindMember
1923	Classes of intangible assets other than goodwill [axis]	Axis			ifrs-full:ClassesOfIntangibleAssetsOtherThanGoodwillAxis
1924	Intangible assets other than goodwill [member]	Member			ifrs-full:IntangibleAssetsOtherThanGoodwillMember
1925	Coal rights	Member			ifrs-full:MiningRightsMember
1926	Software and other	Member			ifrs-full:ComputerSoftwareMember
1927	Power sale contracts	Member			ifrs-full:OtherIntangibleAssetsMember
1928	Intangibles under development	Member			ifrs-full:IntangibleAssetsUnderDevelopmentMember
1929	Carrying amount, accumulated depreciation, amortisation and impairment and gross carrying amount [axis]	Axis			ifrs-full:CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis
1930	Carrying amount [member]	Member			ifrs-full:CarryingAmountMember
1931	Gross carrying amount	Member			ifrs-full:GrossCarryingAmountMember
1932	Accumulated amortization	Member			ifrs-full:AccumulatedDepreciationAndAmortisationMember
1933	Disclosure of reconciliation of changes in intangible assets and goodwill [line items]	LineItems			ifrs-full:DisclosureOfReconciliationOfChangesInIntangibleAssetsAndGoodwillLineItems
1934	Impairment loss	Concept (Monetary)	For Period	Debit	ifrs-full:ImpairmentLoss
1935	Reconciliation of changes in intangible assets other than goodwill [abstract]	Abstract			ifrs-full:ReconciliationOfChangesInIntangibleAssetsOtherThanGoodwillAbstract
1936	Beginning balance	Concept (Monetary)	As Of	Debit	ifrs-full:IntangibleAssetsOtherThanGoodwill
1937	Additions	Concept (Monetary)	For Period	Debit	ifrs-full:AdditionsOtherThanThroughBusinessCombinationsIntangibleAssetsOtherThanGoodwill
1938	Additions other than through business combinations, intangible assets other than goodwill, capital lease	Concept (Monetary)	For Period	Debit	tac:Additionsotherthanthroughbusinesscombinationsintangibleassetsotherthangoodwillcapitallease
1939	Acquisitions through business combinations, intangible assets other than goodwill	Concept (Monetary)	For Period	Debit	ifrs-full:AcquisitionsThroughBusinessCombinationsIntangibleAssetsOtherThanGoodwill
1940	Retirements	Concept (Monetary)	For Period	Credit	ifrs-full:RetirementsIntangibleAssetsOtherThanGoodwill
1941	Change in foreign exchange rates	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughNetExchangeDifferencesIntangibleAssetsOtherThanGoodwill
1942	Transfers	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughTransfersIntangibleAssetsOtherThanGoodwill
1943	Amortization	Concept (Monetary)	For Period		ifrs-full:AmortisationIntangibleAssetsOtherThanGoodwill
1944	Ending balance	Concept (Monetary)	As Of	Debit	ifrs-full:IntangibleAssetsOtherThanGoodwill
1945	2461402 - Disclosure - Other Assets (Details)	Network	*	*	http://www.transalta.com/role/OtherAssetsDetails
1946	Implied Table	Table	*	*	implied:Table
1947	Disclosure of financial assets [abstract]	Abstract			ifrs-full:DisclosureOfFinancialAssetsAbstract
1948	Prepaid Transmission Access And Distribution, Non-Current	Concept (Monetary)	As Of	Debit	tac:PrepaidTransmissionAccessAndDistributionNonCurrent
1949	Deferred licence fees	Concept (Monetary)	As Of	Debit	tac:NoncurrentDeferredLicenseFees
1950	Project development costs	Concept (Monetary)	As Of	Debit	tac:ProjectDevelopmentCostsNoncurrent
1951	Deferred service costs	Concept (Monetary)	As Of	Debit	tac:NoncurrentDeferredServiceCosts
1952	Mississauga long-term receivable (Note 4)	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentReceivablesFromContractsWithCustomers
1953	Long-term prepaids and other assets	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentPrepayments
1954	Loan receivable	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentPortionOfNoncurrentLoansReceived
1955	Keephills Unit 3 transmission deposit	Concept (Monetary)	As Of	Debit	ifrs-full:LongtermDeposits
1956	Total other assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherNoncurrentAssets
1957	2461403 - Disclosure - Other Assets Narrative (Details)	Network	*	*	http://www.transalta.com/role/OtherAssetsNarrativeDetails
1958	Disclosure of joint operations [table]	Table	*	*	ifrs-full:DisclosureOfJointOperationsTable
1959	Classes of financial assets [axis]	Axis			ifrs-full:ClassesOfFinancialAssetsAxis
1960	Financial assets, class [member]	Member			ifrs-full:FinancialAssetsMember
1961	Other assets	Member			ifrs-full:OtherAssetsMember
1962	Categories of financial assets [axis]	Axis			ifrs-full:CategoriesOfFinancialAssetsAxis
1963	Financial assets, category [member]	Member			ifrs-full:FinancialAssetsCategoryMember
1964	Loans and receivables	Member			ifrs-full:LoansAndReceivablesCategoryMember
1965	Levels of fair value hierarchy [axis]	Axis			ifrs-full:LevelsOfFairValueHierarchyAxis
1966	All levels of fair value hierarchy [member]	Member			ifrs-full:AllLevelsOfFairValueHierarchyMember
1967	Level 2 of fair value hierarchy [member]	Member			ifrs-full:Level2OfFairValueHierarchyMember
1968	Measurement [axis]	Axis			ifrs-full:MeasurementAxis
1969	At fair value [member]	Member			ifrs-full:AtFairValueMember
1970	Recurring fair value measurement	Member			ifrs-full:RecurringFairValueMeasurementMember
1971	Categories of financial liabilities [axis]	Axis			ifrs-full:CategoriesOfFinancialLiabilitiesAxis
1972	Financial liabilities, category [member]	Member			ifrs-full:FinancialLiabilitiesCategoryMember
1973	Financial liabilities at fair value through profit or loss, category [member]	Member			ifrs-full:FinancialLiabilitiesAtFairValueThroughProfitOrLossCategoryMember
1974	Classes of financial liabilities [axis]	Axis			ifrs-full:ClassesOfFinancialLiabilitiesAxis
1975	Financial liabilities, class [member]	Member			ifrs-full:FinancialLiabilitiesMember
1976	Long-term Debt1 [Member]	Member			tac:LongtermDebt1Member
1977	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
1978	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
1979	Kent Hills Wind L.P.	Member			tac:KentHillsWindL.P.Member
1980	Joint operations [axis]	Axis			ifrs-full:JointOperationsAxis
1981	Entity's total for joint operations [member]	Member			ifrs-full:EntitysTotalForJointOperationsMember
1982	TAMA Power [Member]	Member			tac:TAMAPowerMember
1983	Disclosure of joint operations [line items]	LineItems			ifrs-full:DisclosureOfJointOperationsLineItems
1984	Current portion of loan receivable (Note 20)	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentLoansAndReceivables
1985	Non-current portion of non-current loans received	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentLoansAndReceivables
1986	Proportion of ownership interest in joint operation	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInJointOperation
1987	Consideration received	Concept (Monetary)	For Period	Credit	ifrs-full:ConsiderationPaidReceived
1988	Financial liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:FinancialLiabilities
1989	Proportion of ownership interests held by non-controlling interests	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestsHeldByNoncontrollingInterests
1990	Interest rate	Concept (Percent)	As Of		ifrs-full:BorrowingsInterestRate
1991	Non-current portion of non-current loans received	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentPortionOfNoncurrentLoansReceived
1992	2464402 - Disclosure - Decommissioning and Other Provisions - Change in Decommissioning and Other Provision Balances (Details)	Network	*	*	http://www.transalta.com/role/DecommissioningAndOtherProvisionsChangeInDecommissioningAndOtherProvisionBalancesDetails
1993	Disclosure of other provisions [table]	Table	*	*	ifrs-full:DisclosureOfOtherProvisionsTable
1994	Classes of other provisions [axis]	Axis			ifrs-full:ClassesOfProvisionsAxis
1995	Other provisions [member]	Member			ifrs-full:OtherProvisionsMember
1996	Decommissioning and restoration	Member			ifrs-full:ProvisionForDecommissioningRestorationAndRehabilitationCostsMember
1997	Other	Member			ifrs-full:MiscellaneousOtherProvisionsMember
1998	Range [axis]	Axis			ifrs-full:RangeAxis
1999	Ranges [member]	Member			ifrs-full:RangesMember
2000	Minimum	Member			ifrs-full:BottomOfRangeMember
2001	Maximum	Member			ifrs-full:TopOfRangeMember
2002	Disclosure of other provisions [line items]	LineItems			ifrs-full:DisclosureOfOtherProvisionsLineItems
2003	Reconciliation of changes in other provisions [abstract]	Abstract			ifrs-full:ReconciliationOfChangesInOtherProvisionsAbstract
2004	Balance	Concept (Monetary)	As Of	Credit	ifrs-full:OtherProvisions
2005	Liabilities incurred	Concept (Monetary)	For Period	Credit	ifrs-full:NewProvisionsOtherProvisions
2006	Liabilities settled	Concept (Monetary)	For Period	Debit	ifrs-full:ProvisionUsedOtherProvisions
2007	Liabilities disposed	Concept (Monetary)	For Period	Debit	tac:ProvisionsDisposed
2008	Accretion	Concept (Monetary)	For Period	Credit	tac:IncreaseThroughAdjustmentsArisingFromPassageOfTimeOtherProvisionsNetOfReceivable
2009	Acquisition of liabilities (Big Level)	Concept (Monetary)	For Period	Credit	ifrs-full:AcquisitionsThroughBusinessCombinationsOtherProvisions
2010	Revisions in estimated cash flows(2)	Concept (Monetary)	For Period	Credit	tac:IncreaseDecreaseThroughChangeInEstimatedCashFlows
2011	Revisions in discount rates(2)	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughChangeInDiscountRateOtherProvisions
2012	Reversals	Concept (Monetary)	For Period	Debit	ifrs-full:UnusedProvisionReversedOtherProvisions
2013	Change in foreign exchange rates	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughNetExchangeDifferencesOtherProvisions
2014	Balance	Concept (Monetary)	As Of	Credit	ifrs-full:OtherProvisions
2015	Use of lower, short-term discount rate (in years)	Concept (xbrli:durationItemType)	For Period		tac:UseofLowerShortTermDiscountRate
2016	Increase (decrease) in discount rates, other provisions	Concept (Percent)	For Period		tac:IncreaseDecreaseinDiscountRatesOtherProvisions
2017	2464403 - Disclosure - Decommissioning and Other Provisions - Current and Non-Current Portion of Decommissioning and Other Provisions (Details)	Network	*	*	http://www.transalta.com/role/DecommissioningAndOtherProvisionsCurrentAndNonCurrentPortionOfDecommissioningAndOtherProvisionsDetails
2018	Disclosure of other provisions [table]	Table	*	*	ifrs-full:DisclosureOfOtherProvisionsTable
2019	Classes of other provisions [axis]	Axis			ifrs-full:ClassesOfProvisionsAxis
2020	Other provisions [member]	Member			ifrs-full:OtherProvisionsMember
2021	Decommissioning and restoration	Member			ifrs-full:ProvisionForDecommissioningRestorationAndRehabilitationCostsMember
2022	Other	Member			ifrs-full:MiscellaneousOtherProvisionsMember
2023	Disclosure of other provisions [line items]	LineItems			ifrs-full:DisclosureOfOtherProvisionsLineItems
2024	Balance	Concept (Monetary)	As Of	Credit	ifrs-full:OtherProvisions
2025	Current portion	Concept (Monetary)	As Of	Credit	ifrs-full:OtherShorttermProvisions
2026	Non-current portion	Concept (Monetary)	As Of	Credit	ifrs-full:OtherLongtermProvisions
2027	2464404 - Disclosure - Decommissioning and Other Provisions - Decommissioning and Restoration (Details)	Network	*	*	http://www.transalta.com/role/DecommissioningAndOtherProvisionsDecommissioningAndRestorationDetails
2028	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
2029	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
2030	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
2031	Centralia Coal Mine	Member			tac:CentraliaCoalMineMember
2032	Alberta Mine	Member			tac:AlbertaMineMember
2033	Classes of financial instruments [axis]	Axis			ifrs-full:ClassesOfFinancialInstrumentsAxis
2034	Financial instruments, class [member]	Member			ifrs-full:ClassesOfFinancialInstrumentsMember
2035	Surety Bonds	Member			tac:SuretyBondsMember
2036	Letters Of Credit [Member]	Member			tac:LettersOfCreditMember
2037	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
2038	Undiscounted cash flows required for future removal of facilities	Concept (Monetary)	As Of	Credit	tac:AssetRetirementObligationUndiscounted
2039	Bonds issued	Concept (Monetary)	As Of	Credit	ifrs-full:ExposureToCreditRiskOnLoanCommitmentsAndFinancialGuaranteeContracts
2040	2464405 - Disclosure - Decommissioning and Other Provisions - Other Provisions (Details)	Network	*	*	http://www.transalta.com/role/DecommissioningAndOtherProvisionsOtherProvisionsDetails
2041	Disclosure of other provisions [table]	Table	*	*	ifrs-full:DisclosureOfOtherProvisionsTable
2042	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
2043	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
2044	Keephills 1	Member			tac:KeephillsOneMember
2045	Disclosure of other provisions [line items]	LineItems			ifrs-full:DisclosureOfOtherProvisionsLineItems
2046	Reversal of unused provision	Concept (Monetary)	For Period	Debit	ifrs-full:UnusedProvisionReversedOtherProvisions
2047	2467402 - Disclosure - Credit Facilities, Long-Term Debt, and Finance Lease Obligations - Amounts Outstanding (Details)	Network	*	*	http://www.transalta.com/role/CreditFacilitiesLongTermDebtAndFinanceLeaseObligationsAmountsOutstandingDetails
2048	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
2049	Range [axis]	Axis			ifrs-full:RangeAxis
2050	Ranges [member]	Member			ifrs-full:RangesMember
2051	Weighted average [member]	Member			ifrs-full:WeightedAverageMember
2052	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
2053	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
2054	All Borrowings Except Finance Lease Obligations [Member]	Member			tac:AllBorrowingsExceptFinanceLeaseObligationsMember
2055	Credit facilities	Member			tac:LineOfCreditFacilityMember
2056	Debentures	Member			tac:UnsecuredDebt1Member
2057	Senior notes	Member			tac:SeniorNotes1Member
2058	Non-recourse	Member			tac:NonRecourseDebtMember
2059	Other	Member			tac:OtherBorrowingsMember
2060	Finance lease obligation	Member			tac:FinanceLeaseObligationMember
2061	Portion Denominated In Foreign Currency [Axis]	Axis			tac:PortionDenominatedInForeignCurrencyAxis
2062	Portion Denominated in Foreign Currency [Domain]	Member			tac:PortionDenominatedInForeignCurrencyDomain
2063	U.S. Dollars	Member			currency:USD
2064	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
2065	Carrying value	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
2066	Notional amount	Concept (Monetary)	As Of		ifrs-full:NotionalAmount
2067	Interest rate	Concept (Percent)	As Of		ifrs-full:BorrowingsInterestRate
2068	Less: current portion of long-term debt	Concept (Monetary)	As Of	Credit	ifrs-full:ShorttermBorrowings
2069	Less: current portion of finance lease obligations	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentFinanceLeaseLiabilities
2070	Total current long-term debt and finance lease obligations	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentBorrowingsAndCurrentPortionOfNoncurrentBorrowings
2071	Credit facilities, long-term debt, and finance lease obligations (Note 22)	Concept (Monetary)	As Of	Credit	ifrs-full:LongtermBorrowings
2072	2467403 - Disclosure - Credit Facilities, Long-Term Debt, and Finance Lease Obligations - Credit Facilities (Details)	Network	*	*	http://www.transalta.com/role/CreditFacilitiesLongTermDebtAndFinanceLeaseObligationsCreditFacilitiesDetails
2073	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
2074	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
2075	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
2076	Corporation and TransAlta Renewables	Member			tac:ParentCompanyandTransAltaRenewablesInc.Member
2077	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
2078	TransAlta OCP	Member			tac:TransAltaOCPMember
2079	Business combinations [axis]	Axis			ifrs-full:BusinessCombinationsAxis
2080	Entity's total for business combinations [member]	Member			ifrs-full:EntitysTotalForBusinessCombinationsMember
2081	Canadian Assets	Member			tac:SarniaCogenerationPlantLeNordaisWindFarmAndRaggedChuteHydroFacilityCanadianAssetsMember
2082	Long-Term Debt, Type [Axis]	Axis			tac:LongTermDebtTypeAxis
2083	Long-Term Debt, Type [Domain]	Member			tac:LongTermDebtTypeDomain
2084	Credit facilities	Member			tac:LineOfCreditFacilityMember
2085	Letter of credit	Member			tac:LetterofCreditMember
2086	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
2087	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
2088	Syndicated Bank Credit Facility [Member]	Member			tac:SyndicatedBankCreditFacilityMember
2089	Committed Bilateral Credit Facilities Expiring In 2019 [Member]	Member			tac:CommittedBilateralCreditFacilitiesExpiringIn2019Member
2090	Committed Bilateral Credit Facilities In 2021 [Member]	Member			tac:CommittedBilateralCreditFacilitiesIn2021Member
2091	Revolving committed syndicated bank facility	Member			tac:RevolvingCommittedSyndicatedBankFacilityMember
2092	Committed bilateral credit facilities expiring in 2018	Member			tac:CommittedBilateralCreditFacilitiesExpiringIn2018Member
2093	Committed bilateral credit facilities expiring in 2020	Member			tac:CommittedBilateralCreditFacilitiesExpiringIn2020Member
2094	Committed credit facilities	Member			tac:CommittedCreditFacilitiesMember
2095	Credit Facility Cancelled In 2017 [Member]	Member			tac:CreditFacilityCancelledIn2017Member
2096	Classes of financial assets [axis]	Axis			ifrs-full:ClassesOfFinancialAssetsAxis
2097	Financial assets, class [member]	Member			ifrs-full:FinancialAssetsMember
2098	Cash and cash equivalents	Member			tac:CashAndCashEquivalents1Member
2099	Categories of financial assets [axis]	Axis			ifrs-full:CategoriesOfFinancialAssetsAxis
2100	Financial assets, category [member]	Member			ifrs-full:FinancialAssetsCategoryMember
2101	Loans and receivables	Member			ifrs-full:LoansAndReceivablesCategoryMember
2102	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
2103	Increase (decrease) in borrowings	Concept (Monetary)	As Of	Credit	tac:IncreaseDecreaseInMaximumBorrowingCapacity
2104	Maximum borrowing capacity under line of credit	Concept (Monetary)	As Of	Credit	tac:LineOfCreditFacilityMaximumBorrowingCapacity1
2105	Line of credit facility, cancelled capacity	Concept (Monetary)	For Period	Credit	tac:LineofCreditFacilityCancelledCapacity
2106	Line of credit facility, increase (decrease)	Concept (Monetary)	For Period	Credit	tac:LineofCreditFacilityIncreaseDecreaseNet1
2107	Term of credit facility	Concept (xbrli:durationItemType)	For Period		tac:TermofCreditFacility
2108	Net cash proceeds	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromLosingControlOfSubsidiariesOrOtherBusinessesClassifiedAsInvestingActivities
2109	Notional amount	Concept (Monetary)	As Of		ifrs-full:NotionalAmount
2110	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
2111	Undrawn borrowing capacity under line of credit	Concept (Monetary)	As Of	Credit	tac:LineOfCreditFacilityRemainingBorrowingCapacity1
2112	Actual drawings on borrowings	Concept (Monetary)	As Of	Credit	tac:LineofCreditCurrent1
2113	Long-term Line Of Credit	Concept (Monetary)	As Of	Credit	tac:LongtermLineOfCredit
2114	Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
2115	Restricted cash (Note 22)	Concept (Monetary)	As Of	Debit	ifrs-full:RestrictedCashAndCashEquivalents
2116	Proceeds from non-current borrowings	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromNoncurrentBorrowings
2117	Restricted cash (Note 22)	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentRestrictedCashAndCashEquivalents
2118	2467404 - Disclosure - Credit Facilities, Long-Term Debt, and Finance Lease Obligations - Debentures (Details)	Network	*	*	http://www.transalta.com/role/CreditFacilitiesLongTermDebtAndFinanceLeaseObligationsDebenturesDetails
2119	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
2120	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
2121	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
2122	Debentures	Member			tac:UnsecuredDebt1Member
2123	Range [axis]	Axis			ifrs-full:RangeAxis
2124	Ranges [member]	Member			ifrs-full:RangesMember
2125	Minimum	Member			ifrs-full:BottomOfRangeMember
2126	Maximum	Member			ifrs-full:TopOfRangeMember
2127	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
2128	Notional amount	Concept (Monetary)	As Of		ifrs-full:NotionalAmount
2129	Redemption of unsecured debt	Concept (Monetary)	For Period	Credit	tac:RedemptionofNoncurrentBorrowings
2130	Redemption of prepayment premium recognized in net interest expense	Concept (Monetary)	For Period	Credit	tac:RedemptionofNoncurrentBorrowingsPremium
2131	Accrued and unpaid interest	Concept (Monetary)	For Period	Credit	tac:RedemptionofNoncurrentBorrowingsAccruedInterest
2132	Interest rate	Concept (Percent)	As Of		ifrs-full:BorrowingsInterestRate
2133	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
2134	Alberta off-coal agreement, annual cash payments, gross	Concept (Monetary)	For Period	Credit	tac:GainsLossesonContractAgreement
2135	Alberta off-coal agreement, annual cash payments, net	Concept (Monetary)	For Period	Credit	tac:GainsLossesonContractAgreementNet
2136	2467405 - Disclosure - Credit Facilities, Long-Term Debt, and Finance Lease Obligations - Senior Notes (Details)	Network	*	*	http://www.transalta.com/role/CreditFacilitiesLongTermDebtAndFinanceLeaseObligationsSeniorNotesDetails
2137	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
2138	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
2139	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
2140	Melancthon-Wolfe Wind	Member			tac:MelancthonWolfeWindL.PMember
2141	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
2142	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
2143	6.65% Senior notes, due May 2018	Member			tac:SeniorNotes500Million6.65PercentDueMay2018Member
2144	4.75% Senior Notes due 2015	Member			tac:A4.75SeniorNotesDue2015Member
2145	3.834% Non-Recourse Bond due 2028	Member			tac:A3.834NonRecourseBondDue2028Member
2146	Non-Recourse Bonds	Member			tac:NonRecourseBondsMember
2147	Long-Term Debt, Type [Axis]	Axis			tac:LongTermDebtTypeAxis
2148	Long-Term Debt, Type [Domain]	Member			tac:LongTermDebtTypeDomain
2149	Senior notes	Member			tac:SeniorNotes1Member
2150	Non-recourse	Member			tac:NonRecourseDebtMember
2151	Hedging Designation [Axis]	Axis			tac:HedgingDesignation1Axis
2152	Hedging Designation [Member]	Member			tac:HedgingDesignation1Member
2153	Designated as hedging instrument	Member			tac:DesignatedasHedgingInstrumentMember
2154	Range [axis]	Axis			ifrs-full:RangeAxis
2155	Ranges [member]	Member			ifrs-full:RangesMember
2156	Minimum	Member			ifrs-full:BottomOfRangeMember
2157	Maximum	Member			ifrs-full:TopOfRangeMember
2158	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
2159	Interest rate	Concept (Percent)	As Of		ifrs-full:BorrowingsInterestRate
2160	Notional amount	Concept (Monetary)	As Of		ifrs-full:NotionalAmount
2161	Redemption of unsecured debt, principal	Concept (Monetary)	For Period	Credit	tac:RedemptionofNoncurrentBorrowingsPrincipal
2162	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
2163	Redemption of noncurrent borrowings	Concept (Monetary)	For Period	Credit	tac:RedemptionofNoncurrentBorrowings
2164	Redemption of prepayment premium recognized in net interest expense	Concept (Monetary)	For Period	Credit	tac:RedemptionofNoncurrentBorrowingsPremium
2165	Accrued and unpaid interest	Concept (Monetary)	For Period	Credit	tac:RedemptionofNoncurrentBorrowingsAccruedInterest
2166	2467406 - Disclosure - Credit Facilities, Long-Term Debt, and Finance Lease Obligations - Non-Recourse Debt (Details)	Network	*	*	http://www.transalta.com/role/CreditFacilitiesLongTermDebtAndFinanceLeaseObligationsNonRecourseDebtDetails
2167	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
2168	Business combinations [axis]	Axis			ifrs-full:BusinessCombinationsAxis
2169	Entity's total for business combinations [member]	Member			ifrs-full:EntitysTotalForBusinessCombinationsMember
2170	Solar assets	Member			tac:RCSolarLLCMember
2171	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
2172	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
2173	TransAlta OCP	Member			tac:TransAltaOCPMember
2174	New Richmond	Member			tac:NewRichmondWindL.P.Member
2175	Melancthon-Wolfe Wind	Member			tac:MelancthonWolfeWindL.PMember
2176	TAPC Holdings	Member			tac:TAPCHoldingsL.P.Member
2177	Joint operations [axis]	Axis			ifrs-full:JointOperationsAxis
2178	Entity's total for joint operations [member]	Member			ifrs-full:EntitysTotalForJointOperationsMember
2179	Pingston	Member			tac:PingstonMember
2180	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
2181	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
2182	5.69% Non-Recourse Debenture due 2016	Member			tac:A5.69NonRecourseDebentureDue2016Member
2183	3.963% Non-Recourse Bond due 2032	Member			tac:A3.963NonRecourseBondDue2032Member
2184	3.834% Non-Recourse Bond due 2028	Member			tac:A3.834NonRecourseBondDue2028Member
2185	Variable Rate Bond due 2030	Member			tac:VariableRateBondDue2030Member
2186	Non-Recourse Bonds	Member			tac:NonRecourseBondsMember
2187	2.95% Non-Recourse Bonds due 2023	Member			tac:A2.95NonRecourseBondsDueMay2023Member
2188	5.28% Non-Recourse Debenture	Member			tac:A5.28NonRecourseDebentureMember
2189	5.33% Non-Recourse Debentures Due 2015	Member			tac:A5.33NonRecourseDebenturesDue2015Member
2190	Non-Recourse Variable Rate Debt	Member			tac:NonRecourseVariableRateDebtMember
2191	Long-Term Debt, Type [Axis]	Axis			tac:LongTermDebtTypeAxis
2192	Long-Term Debt, Type [Domain]	Member			tac:LongTermDebtTypeDomain
2193	Non-recourse debt	Member			tac:NonRecourseDebtMember
2194	Variable Rate [Axis]	Axis			tac:VariableRate1Axis
2195	Variable Rate [Domain]	Member			tac:VariableRate1Domain
2196	Canadian Dollar Offered Rate	Member			tac:CanadianDollarOfferedRateMember
2197	Hedging Designation [Axis]	Axis			tac:HedgingDesignation1Axis
2198	Hedging Designation [Member]	Member			tac:HedgingDesignation1Member
2199	Hedged item	Member			ifrs-full:HedgedItemsMember
2200	Range [axis]	Axis			ifrs-full:RangeAxis
2201	Ranges [member]	Member			ifrs-full:RangesMember
2202	Minimum	Member			ifrs-full:BottomOfRangeMember
2203	Maximum	Member			ifrs-full:TopOfRangeMember
2204	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
2205	Borrowings, adjustment to interest rate basis	Concept (Percent)	As Of		ifrs-full:BorrowingsAdjustmentToInterestRateBasis
2206	Interest rate	Concept (Percent)	As Of		ifrs-full:BorrowingsInterestRate
2207	Notional amount	Concept (Monetary)	As Of		ifrs-full:NotionalAmount
2208	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
2209	Bonds issued	Concept (Monetary)	As Of	Credit	ifrs-full:BondsIssued
2210	Redemption of noncurrent borrowings	Concept (Monetary)	For Period	Credit	tac:RedemptionofNoncurrentBorrowings
2211	Principal payment	Concept (Monetary)	For Period	Credit	ifrs-full:RepaymentsOfNoncurrentBorrowings
2212	Loss on early redemption of bonds	Concept (Monetary)	For Period	Debit	tac:LossOnRedemptionOfBonds
2213	Financial liabilities recognised as of acquisition date	Concept (Monetary)	As Of	Credit	ifrs-full:FinancialLiabilitiesRecognisedAsOfAcquisitionDate
2214	2467407 - Disclosure - Credit Facilities, Long-Term Debt, and Finance Lease Obligations - Other (Details)	Network	*	*	http://www.transalta.com/role/CreditFacilitiesLongTermDebtAndFinanceLeaseObligationsOtherDetails
2215	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
2216	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
2217	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
2218	TransAlta OCP	Member			tac:TransAltaOCPMember
2219	Kent Hills Wind L.P.	Member			tac:KentHillsWindL.P.Member
2220	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
2221	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
2222	Renewable generation facilities	Member			ifrs-full:PowerGeneratingAssetsMember
2223	Long-Term Debt, Type [Axis]	Axis			tac:LongTermDebtTypeAxis
2224	Long-Term Debt, Type [Domain]	Member			tac:LongTermDebtTypeDomain
2225	Other	Member			tac:OtherBorrowingsMember
2226	Non-recourse	Member			tac:NonRecourseDebtMember
2227	Secured Debt	Member			tac:SecuredDebt1Member
2228	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
2229	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
2230	5.9% Unsecured Commercial Loan Obligation due 2023	Member			tac:A5.9UnsecuredCommercialLoanObligationDue2023Member
2231	Secured by first rate ranking charge over subsidiaries	Member			tac:SecuredByChargesOverAssetsOfSubsidiariesMember
2232	Secured by equity interests of the issuer	Member			tac:SecuredbyequityinterestsoftheissuerMember
2233	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
2234	Restricted cash (Note 22)	Concept (Monetary)	As Of	Debit	ifrs-full:RestrictedCashAndCashEquivalents
2235	Interest rate	Concept (Percent)	As Of		ifrs-full:BorrowingsInterestRate
2236	Notional amount	Concept (Monetary)	As Of		ifrs-full:NotionalAmount
2237	Property, plant and equipment (Note 17)	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
2238	2467408 - Disclosure - Credit Facilities, Long-Term Debt, and Finance Lease Obligations - Restrictions on Non-Recourse Debt and Security (Details)	Network	*	*	http://www.transalta.com/role/CreditFacilitiesLongTermDebtAndFinanceLeaseObligationsRestrictionsOnNonRecourseDebtAndSecurityDetails
2239	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
2240	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
2241	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
2242	Renewable generation facilities	Member			ifrs-full:PowerGeneratingAssetsMember
2243	Long-Term Debt, Type [Axis]	Axis			tac:LongTermDebtTypeAxis
2244	Long-Term Debt, Type [Domain]	Member			tac:LongTermDebtTypeDomain
2245	Non-recourse debt	Member			tac:NonRecourseDebtMember
2246	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
2247	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
2248	Secured by first rate ranking charge over subsidiaries	Member			tac:SecuredByChargesOverAssetsOfSubsidiariesMember
2249	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
2250	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
2251	CHD	Member			tac:CHDMember
2252	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
2253	Debentures issued	Concept (Monetary)	As Of	Credit	ifrs-full:NotesAndDebenturesIssued
2254	Other borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:OtherBorrowings
2255	Restricted cash (Note 22)	Concept (Monetary)	As Of	Debit	ifrs-full:RestrictedCashAndCashEquivalents
2256	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
2257	Property, plant and equipment (Note 17)	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
2258	Bonds issued	Concept (Monetary)	As Of	Credit	ifrs-full:BondsIssued
2259	Cash on deposit, non-recourse bonds	Concept (Monetary)	As Of	Debit	tac:CashReservesonNonRecourseBonds
2260	2467409 - Disclosure - Credit Facilities, Long-Term Debt, and Finance Lease Obligations - Principal Repayments (Details)	Network	*	*	http://www.transalta.com/role/CreditFacilitiesLongTermDebtAndFinanceLeaseObligationsPrincipalRepaymentsDetails
2261	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
2262	Carrying amount, accumulated depreciation, amortisation and impairment and gross carrying amount [axis]	Axis			ifrs-full:CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis
2263	Carrying amount [member]	Member			ifrs-full:CarryingAmountMember
2264	Gross carrying amount	Member			ifrs-full:GrossCarryingAmountMember
2265	Maturity [axis]	Axis			ifrs-full:MaturityAxis
2266	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
2267	2018	Member			ifrs-full:NotLaterThanOneYearMember
2268	2019	Member			ifrs-full:LaterThanOneYearAndNotLaterThanTwoYearsMember
2269	2020	Member			ifrs-full:LaterThanTwoYearsAndNotLaterThanThreeYearsMember
2270	2021	Member			ifrs-full:LaterThanThreeYearsAndNotLaterThanFourYearsMember
2271	2022	Member			ifrs-full:LaterThanFourYearsAndNotLaterThanFiveYearsMember
2272	2023 and thereafter	Member			ifrs-full:LaterThanFiveYearsMember
2273	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
2274	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
2275	2467410 - Disclosure - Credit Facilities, Long-Term Debt, and Finance Lease Obligations - Finance Lease Obligations (Details)	Network	*	*	http://www.transalta.com/role/CreditFacilitiesLongTermDebtAndFinanceLeaseObligationsFinanceLeaseObligationsDetails
2276	Disclosure of finance lease and operating lease by lessee [table]	Table	*	*	ifrs-full:DisclosureOfFinanceLeaseAndOperatingLeaseByLesseeTable
2277	Long-Term Debt, Type [Axis]	Axis			tac:LongTermDebtTypeAxis
2278	Long-Term Debt, Type [Domain]	Member			tac:LongTermDebtTypeDomain
2279	Letter of credit	Member			tac:LetterofCreditMember
2280	Maturity [axis]	Axis			ifrs-full:MaturityAxis
2281	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
2282	Within one year	Member			ifrs-full:NotLaterThanOneYearMember
2283	Second to fifth years inclusive	Member			ifrs-full:LaterThanTwoYearsAndNotLaterThanFiveYearsMember
2284	More than five years	Member			ifrs-full:LaterThanFiveYearsMember
2285	Disclosure of finance lease and operating lease by lessee [line items]	LineItems			ifrs-full:DisclosureOfFinanceLeaseAndOperatingLeaseByLesseeLineItems
2286	Minimum lease payments	Concept (Monetary)	As Of	Credit	ifrs-full:MinimumFinanceLeasePaymentsPayable
2287	Present value of minimum lease payments	Concept (Monetary)	As Of	Credit	ifrs-full:MinimumFinanceLeasePaymentsPayableAtPresentValue
2288	Less: interest costs	Concept (Monetary)	As Of	Credit	ifrs-full:FutureFinanceChargeOnFinanceLease
2289	Total finance lease obligations	Concept (Monetary)	As Of	Credit	ifrs-full:FinanceLeaseLiabilities
2290	Current portion of finance lease obligations	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentFinanceLeaseLiabilities
2291	Long-term portion of finance lease obligations	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentFinanceLeaseLiabilities
2292	2467411 - Disclosure - Credit Facilities, Long-Term Debt, and Finance Lease Obligations - Letters of Credit (Details)	Network	*	*	http://www.transalta.com/role/CreditFacilitiesLongTermDebtAndFinanceLeaseObligationsLettersOfCreditDetails
2293	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
2294	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
2295	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
2296	4.75% Senior Notes due 2015	Member			tac:A4.75SeniorNotesDue2015Member
2297	Committed bilateral credit facilities	Member			tac:CommittedBilateralCreditFacilitiesMember
2298	Uncommitted demand letter facility	Member			tac:UncommittedDemandLetterFacilityMember
2299	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
2300	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
2301	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
2302	Classes of financial instruments [axis]	Axis			ifrs-full:ClassesOfFinancialInstrumentsAxis
2303	Financial instruments, class [member]	Member			ifrs-full:ClassesOfFinancialInstrumentsMember
2304	Letter of credit	Member			tac:LetterofCreditMember
2305	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
2306	Maximum borrowing capacity under line of credit	Concept (Monetary)	As Of	Credit	tac:LineOfCreditFacilityMaximumBorrowingCapacity1
2307	Exposure to credit risk on loan commitments and financial guarantee contracts	Concept (Monetary)	As Of	Credit	ifrs-full:ExposureToCreditRiskOnLoanCommitmentsAndFinancialGuaranteeContracts
2308	Amount exercised under letters of credit	Concept (Monetary)	As Of	Credit	tac:AmountExercisedUnderLettersOfCredit
2309	2470402 - Disclosure - Defined Benefit Obligation and Other Long-Term Liabilities (Details)	Network	*	*	http://www.transalta.com/role/DefinedBenefitObligationAndOtherLongTermLiabilitiesDetails
2310	Implied Table	Table	*	*	implied:Table
2311	Subclassifications of assets, liabilities and equities [abstract]	Abstract			ifrs-full:SubclassificationsOfAssetsLiabilitiesAndEquitiesAbstract
2312	Defined benefit obligation (Note 28)	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentRecognisedLiabilitiesDefinedBenefitPlan
2313	Long-term incentive accruals (Note 27)	Concept (Monetary)	As Of	Credit	ifrs-full:AccrualsClassifiedAsNoncurrent
2314	Other	Concept (Monetary)	As Of	Credit	ifrs-full:OtherNoncurrentLiabilities
2315	Total(1)	Concept (Monetary)	As Of	Credit	tac:NoncurrentDefinedBenefitObligationAndOtherLongtermLiabilities
2316	Contract liabilities (Note 5)	Concept (Monetary)	As Of	Credit	ifrs-full:ContractLiabilities
2317	2473402 - Disclosure - Common Shares - Issued and Outstanding (Details)	Network	*	*	http://www.transalta.com/role/CommonSharesIssuedAndOutstandingDetails
2318	Disclosure of classes of share capital [table]	Table	*	*	ifrs-full:DisclosureOfClassesOfShareCapitalTable
2319	Classes of share capital [axis]	Axis			ifrs-full:ClassesOfShareCapitalAxis
2320	Share capital [member]	Member			ifrs-full:ClassesOfShareCapitalMember
2321	Common shares	Member			tac:CommonsharesMember
2322	Disclosure of classes of share capital [line items]	LineItems			ifrs-full:DisclosureOfClassesOfShareCapitalLineItems
2323	Issued and outstanding, end of year	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
2324	Proceeds from issuing shares	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromIssuingShares
2325	Issued Capital, Amount Before Receivables Under Employee Share Purchase Plan	Concept (Monetary)	As Of	Credit	tac:IssuedCapitalAmountBeforeReceivablesUnderEmployeeSharePurchasePlan
2326	Amounts receivable under Employee Share Purchase Plan	Concept (Monetary)	For Period	Debit	tac:ReceivablesUnderEmployeeSharePurchasePlan
2327	Issued and outstanding, end of year	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
2328	Common shares	Abstract			ifrs-full:ReconciliationOfNumberOfSharesOutstandingAbstract
2329	Issued and outstanding, beginning of year	Concept (Shares)	As Of		ifrs-full:NumberOfSharesOutstanding
2330	Shares issued	Concept (Shares)	For Period		ifrs-full:IncreaseDecreaseInNumberOfSharesOutstanding
2331	Issued and outstanding, end of year	Concept (Shares)	As Of		ifrs-full:NumberOfSharesOutstanding
2332	2473403 - Disclosure - Common Shares - The effects of the Corporation's purchase and cancellation of the common shares (Details)	Network	*	*	http://www.transalta.com/role/CommonSharesEffectsOfCorporationsPurchaseAndCancellationOfCommonSharesDetails
2333	Disclosure of classes of share capital [table]	Table	*	*	ifrs-full:DisclosureOfClassesOfShareCapitalTable
2334	Classes of share capital [axis]	Axis			ifrs-full:ClassesOfShareCapitalAxis
2335	Share capital [member]	Member			ifrs-full:ClassesOfShareCapitalMember
2336	NCIB Program	Member			tac:NCIBProgramMember
2337	Common shares	Member			tac:CommonsharesMember
2338	Disclosure of classes of share capital [line items]	LineItems			ifrs-full:DisclosureOfClassesOfShareCapitalLineItems
2339	Number of shares issued and fully paid	Concept (Shares)	As Of		ifrs-full:NumberOfSharesIssuedAndFullyPaid
2340	Par value per share	Concept (Share)	As Of		ifrs-full:ParValuePerShare
2341	Issued capital (Note 24)	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
2342	Weighted average share price	Concept (Monetary)	For Period		ifrs-full:WeightedAverageSharePrice
2343	Deficit	Concept (Monetary)	As Of	Credit	ifrs-full:RetainedEarnings
2344	2473404 - Disclosure - Common Shares - Shareholder Rights Plan (Details)	Network	*	*	http://www.transalta.com/role/CommonSharesShareholderRightsPlanDetails
2345	Disclosure of classes of share capital [table]	Table	*	*	ifrs-full:DisclosureOfClassesOfShareCapitalTable
2346	Plan Name [Axis]	Axis			tac:PlanName1Axis
2347	Plan Name [Domain]	Member			tac:PlanName1Domain
2348	Shareholder Rights Plan	Member			tac:ShareholderRightsPlanMember
2349	Classes of share capital [axis]	Axis			ifrs-full:ClassesOfShareCapitalAxis
2350	Share capital [member]	Member			ifrs-full:ClassesOfShareCapitalMember
2351	Common shares	Member			tac:CommonsharesMember
2352	Range [axis]	Axis			ifrs-full:RangeAxis
2353	Ranges [member]	Member			ifrs-full:RangesMember
2354	Minimum	Member			ifrs-full:BottomOfRangeMember
2355	Disclosure of classes of share capital [line items]	LineItems			ifrs-full:DisclosureOfClassesOfShareCapitalLineItems
2356	Percentage of outstanding common shares at which Shareholder Rights Plan may take effect	Concept (Percent)	For Period		tac:ShareholderRightsPlanPercentageOfOutstandingCommonSharesPotentiallyPurchasedAtWhichShareholderRightsAreExercisable
2357	Value of common shares received under Shareholder Rights Plan	Concept (Monetary)	For Period		tac:ValueOfCommonSharesReceivedUnderShareholderRights
2358	Purchase price of common shares under Shareholder Rights Plan	Concept (Monetary)	For Period		tac:PurchasePriceOfCommonSharesUnderShareholderRights
2359	2473405 - Disclosure - Common Shares - Earnings per Common Share (Details)	Network	*	*	http://www.transalta.com/role/CommonSharesEarningsPerCommonShareDetails
2360	Implied Table	Table	*	*	implied:Table
2361	Earnings per share [abstract]	Abstract			ifrs-full:EarningsPerShareAbstract
2362	Net earnings (loss) attributable to common shareholders	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossAttributableToOrdinaryEquityHoldersOfParentEntity
2363	Basic and diluted weighted average number of common shares outstanding (millions)	Concept (Shares)	For Period		ifrs-full:WeightedAverageShares
2364	Net earnings (loss) per share attributable to common shareholders, basic and diluted (in CAD per share)	Concept (Share)	For Period		ifrs-full:BasicAndDilutedEarningsLossPerShare
2365	2473406 - Disclosure - Common Shares - Dividends (Details)	Network	*	*	http://www.transalta.com/role/CommonSharesDividendsDetails
2366	Implied Table	Table	*	*	implied:Table
2367	Share Capital, Reserves And Other Equity Interest [Abstract]	Abstract			tac:ShareCapitalReservesAndOtherEquityInterestAbstract
2368	Annual dividend per share	Concept (Share)	As Of		tac:AnnualDividendPerShare
2369	Dividends declared per share	Concept (Share)	For Period		ifrs-full:DividendsProposedOrDeclaredBeforeFinancialStatementsAuthorisedForIssueButNotRecognisedAsDistributionToOwnersPerShare
2370	2476402 - Disclosure - Preferred Shares - Issued and Outstanding (Details)	Network	*	*	http://www.transalta.com/role/PreferredSharesIssuedAndOutstandingDetails
2371	Disclosure of classes of share capital [table]	Table	*	*	ifrs-full:DisclosureOfClassesOfShareCapitalTable
2372	Classes of share capital [axis]	Axis			ifrs-full:ClassesOfShareCapitalAxis
2373	Share capital [member]	Member			ifrs-full:ClassesOfShareCapitalMember
2374	Preferred Shares	Member			ifrs-full:PreferenceSharesMember
2375	Series A	Member			tac:PreferenceSharesSeriesAMember
2376	Series B	Member			tac:PreferenceSharesSeriesBMember
2377	Series C	Member			tac:PreferenceSharesSeriesCMember
2378	Series E	Member			tac:PreferenceSharesSeriesEMember
2379	Series G	Member			tac:PreferenceSharesSeriesGMember
2380	Disclosure of classes of share capital [line items]	LineItems			ifrs-full:DisclosureOfClassesOfShareCapitalLineItems
2381	Number of shares outstanding	Concept (Shares)	As Of		ifrs-full:NumberOfSharesOutstanding
2382	Number of shares issued and outstanding	Concept (Shares)	As Of		ifrs-full:NumberOfSharesIssued
2383	Issued capital (Note 25)	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
2384	2476403 - Disclosure - Preferred Shares - Series A Cumulative Fixed Redeemable Rate Reset Preferred Shares Conversion (Details)	Network	*	*	http://www.transalta.com/role/PreferredSharesSeriesCumulativeFixedRedeemableRateResetPreferredSharesConversionDetails
2385	Disclosure of classes of share capital [table]	Table	*	*	ifrs-full:DisclosureOfClassesOfShareCapitalTable
2386	Classes of share capital [axis]	Axis			ifrs-full:ClassesOfShareCapitalAxis
2387	Share capital [member]	Member			ifrs-full:ClassesOfShareCapitalMember
2388	Series A	Member			tac:PreferenceSharesSeriesAMember
2389	Series F	Member			tac:PreferenceSharesSeriesFMember
2390	Series B	Member			tac:PreferenceSharesSeriesBMember
2391	Series E	Member			tac:PreferenceSharesSeriesEMember
2392	Series D	Member			tac:PreferenceSharesSeriesDMember
2393	Series C	Member			tac:PreferenceSharesSeriesCMember
2394	Disclosure of classes of share capital [line items]	LineItems			ifrs-full:DisclosureOfClassesOfShareCapitalLineItems
2395	Number of shares converted into other classes of shares	Concept (Shares)	As Of		tac:ConvertiblePreferredSharesConvertedToOtherSecurities
2396	Number of shares issued upon conversion	Concept (Shares)	As Of		ifrs-full:NumberOfSharesIssued
2397	Shares Required To Cause Conversion of Securities, Trigger	Concept (Shares)	For Period		tac:SharesRequiredToCauseConversionofSecuritiesTrigger
2398	Number of shares outstanding	Concept (Shares)	As Of		ifrs-full:NumberOfSharesOutstanding
2399	Payment period for cumulative preferential cash dividends	Concept (xbrli:durationItemType)	For Period		tac:TermOfPreferenceSharesDividendDistribution
2400	Annualized fixed dividend rate	Concept (Percent)	For Period		tac:DividendRateOnPreferenceShares
2401	2476404 - Disclosure - Preferred Shares - Preferred Share Series Information (Details)	Network	*	*	http://www.transalta.com/role/PreferredSharesPreferredShareSeriesInformationDetails
2402	Disclosure of classes of share capital [table]	Table	*	*	ifrs-full:DisclosureOfClassesOfShareCapitalTable
2403	Classes of share capital [axis]	Axis			ifrs-full:ClassesOfShareCapitalAxis
2404	Share capital [member]	Member			ifrs-full:ClassesOfShareCapitalMember
2405	Series E	Member			tac:PreferenceSharesSeriesEMember
2406	Preferred Shares	Member			ifrs-full:PreferenceSharesMember
2407	Series C	Member			tac:PreferenceSharesSeriesCMember
2408	Disclosure of classes of share capital [line items]	LineItems			ifrs-full:DisclosureOfClassesOfShareCapitalLineItems
2409	Convertible preferred shares tendered for conversion	Concept (Shares)	As Of		tac:ConvertiblePreferredSharesTenderedForConversion
2410	Fixed rate reset term	Concept (xbrli:durationItemType)	For Period		tac:PreferenceSharesFixedRateResetTerm
2411	Amount per share redeemable at reset date	Concept (Share)	For Period		tac:AmountPerShareRedeemableAtResetDate
2412	Annualized fixed dividend rate	Concept (Percent)	For Period		tac:DividendRateOnPreferenceShares
2413	Bond yield	Concept (Percent)	For Period		tac:BondYield
2414	Dividend rate on preference shares, term	Concept (Percent)	For Period		tac:DividendRateOnPreferenceSharesSpread
2415	2476405 - Disclosure - Preferred Shares - Characteristics Specific to Series of Preferred Shares (Details)	Network	*	*	http://www.transalta.com/role/PreferredSharesCharacteristicsSpecificToSeriesOfPreferredSharesDetails
2416	Disclosure of classes of share capital [table]	Table	*	*	ifrs-full:DisclosureOfClassesOfShareCapitalTable
2417	Classes of share capital [axis]	Axis			ifrs-full:ClassesOfShareCapitalAxis
2418	Share capital [member]	Member			ifrs-full:ClassesOfShareCapitalMember
2419	Series A	Member			tac:PreferenceSharesSeriesAMember
2420	Series B	Member			tac:PreferenceSharesSeriesBMember
2421	Series C	Member			tac:PreferenceSharesSeriesCMember
2422	Series D	Member			tac:PreferenceSharesSeriesDMember
2423	Series E	Member			tac:PreferenceSharesSeriesEMember
2424	Series F	Member			tac:PreferenceSharesSeriesFMember
2425	Series G	Member			tac:PreferenceSharesSeriesGMember
2426	Series H	Member			tac:PreferenceSharesSeriesHMember
2427	Variable Rate [Axis]	Axis			tac:VariableRate1Axis
2428	Variable Rate [Domain]	Member			tac:VariableRate1Domain
2429	Benchmark	Member			tac:BenchmarkMember
2430	Disclosure of classes of share capital [line items]	LineItems			ifrs-full:DisclosureOfClassesOfShareCapitalLineItems
2431	Annual dividend rate per share	Concept (Share)	As Of		tac:AnnualDividendPerShare
2432	Rate spread over Benchmark	Concept (Percent)	For Period		tac:PreferenceSharesBasisSpreadOnVariableRate
2433	2476406 - Disclosure - Preferred Shares - Preferred Share Dividends Declared (Details)	Network	*	*	http://www.transalta.com/role/PreferredSharesPreferredShareDividendsDeclaredDetails
2434	Disclosure of classes of share capital [table]	Table	*	*	ifrs-full:DisclosureOfClassesOfShareCapitalTable
2435	Classes of share capital [axis]	Axis			ifrs-full:ClassesOfShareCapitalAxis
2436	Share capital [member]	Member			ifrs-full:ClassesOfShareCapitalMember
2437	Series A	Member			tac:PreferenceSharesSeriesAMember
2438	Series B	Member			tac:PreferenceSharesSeriesBMember
2439	Series C	Member			tac:PreferenceSharesSeriesCMember
2440	Series E	Member			tac:PreferenceSharesSeriesEMember
2441	Series G	Member			tac:PreferenceSharesSeriesGMember
2442	Preferred Shares	Member			ifrs-full:PreferenceSharesMember
2443	Disclosure of classes of share capital [line items]	LineItems			ifrs-full:DisclosureOfClassesOfShareCapitalLineItems
2444	Dividends declared	Concept (Monetary)	For Period	Debit	ifrs-full:DividendsRecognisedAsDistributionsToOwnersOfParent
2445	Dividends declared per share	Concept (Share)	For Period		ifrs-full:DividendsProposedOrDeclaredBeforeFinancialStatementsAuthorisedForIssueButNotRecognisedAsDistributionToOwnersPerShare
2446	2479402 - Disclosure - Accumulated Other Comprehensive Income (Details)	Network	*	*	http://www.transalta.com/role/AccumulatedOtherComprehensiveIncomeDetails
2447	Disclosure of analysis of other comprehensive income by item [table]	Table	*	*	ifrs-full:DisclosureOfAnalysisOfOtherComprehensiveIncomeByItemTable
2448	Components of equity [axis]	Axis			ifrs-full:ComponentsOfEquityAxis
2449	Equity [member]	Member			ifrs-full:EquityMember
2450	Reserve of exchange differences on translation	Member			ifrs-full:ReserveOfExchangeDifferencesOnTranslationMember
2451	Reserve of cash flow hedges [member]	Member			ifrs-full:ReserveOfCashFlowHedgesMember
2452	Reserve of remeasurements of defined benefit plans [member]	Member			ifrs-full:ReserveOfRemeasurementsOfDefinedBenefitPlansMember
2453	Other reserves [member]	Member			ifrs-full:OtherReservesMember
2454	Disclosure of analysis of other comprehensive income by item [line items]	LineItems			ifrs-full:DisclosureOfAnalysisOfOtherComprehensiveIncomeByItemLineItems
2455	Components and changes in accumulated other comprehensive Income (loss)	Abstract			ifrs-full:MiscellaneousEquityAbstract
2456	Accumulated other comprehensive income, beginning of the period	Concept (Monetary)	As Of	Credit	ifrs-full:AccumulatedOtherComprehensiveIncome
2457	Currency translation adjustment	Abstract			ifrs-full:ExchangeDifferencesOnTranslationAbstract
2458	Losses on translating net assets of foreign operations, net of reclassifications to net earnings, net of tax	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnExchangeDifferencesOnTranslationNetOfTax
2459	Gains (losses) on financial instruments designated as hedges of foreign operations, net of tax	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnHedgesOfNetInvestmentsInForeignOperationsNetOfTax
2460	Cash flow hedges	Abstract			ifrs-full:CashFlowHedgesAbstract
2461	Gains (losses) on derivatives designated as cash flow hedges, net of tax	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnCashFlowHedgesNetOfTax
2462	Employee future benefits	Abstract			tac:EmployeeBenefitsAbstract
2463	Net actuarial gains (losses) on defined benefit plans, net of tax	Concept (Monetary)	For Period	Debit	ifrs-full:ActuarialGainsLossesArisingFromChangesInFinancialAssumptionsNetDefinedBenefitLiabilityAsset
2464	Other	Abstract			ifrs-full:OtherProvisionsAbstract
2465	Change in ownership of TransAlta Renewables	Concept (Monetary)	For Period	Credit	tac:ChangeInOwnershipOfSubsidiary
2466	Intercompany available-for-sale investments	Concept (Monetary)	For Period	Credit	tac:IntercompanyAvailableForSaleInvestments
2467	Accumulated other comprehensive income, end of the period	Concept (Monetary)	As Of	Credit	ifrs-full:AccumulatedOtherComprehensiveIncome
2468	Income tax relating to exchange differences on translation of other comprehensive income	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxRelatingToExchangeDifferencesOnTranslationOfOtherComprehensiveIncome
2469	Income tax relating to hedges of net investments in foreign operations of other comprehensive income	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxRelatingToHedgesOfNetInvestmentsInForeignOperationsOfOtherComprehensiveIncome
2470	Net impact related to cash flow hedges	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxRelatingToCashFlowHedgesOfOtherComprehensiveIncome
2471	Income tax relating to net actuarial gains (losses)	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxRelatingToRemeasurementsOfDefinedBenefitPlansOfOtherComprehensiveIncome
2472	2482402 - Disclosure - Share-Based Payment Plans (Details)	Network	*	*	http://www.transalta.com/role/ShareBasedPaymentPlansDetails
2473	Disclosure of terms and conditions of share-based payment arrangement [table]	Table	*	*	ifrs-full:DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable
2474	Types of share-based payment arrangements [axis]	Axis			ifrs-full:TypesOfSharebasedPaymentArrangementsAxis
2475	Share-based payment arrangements [member]	Member			ifrs-full:SharebasedPaymentArrangementsMember
2476	PSUs and RSUs	Member			tac:PerformanceShareUnitPSUandRestrictedShareUnitRSUPlanMember
2477	PSUs	Member			tac:PerformanceShareUnitPSUMember
2478	RSUs	Member			tac:RestrictedShareUnitRSUMember
2479	DSUs	Member			tac:DeferredShareUnitDSUMember
2480	Stock Options	Member			tac:StockOptionsMember
2481	Employee Share Purchase Plan	Member			tac:EmployeeSharePurchasePlanMember
2482	Title of Individuals [Axis]	Axis			tac:TitleofIndividuals1Axis
2483	Title of Individuals1 [Member]	Member			tac:TitleofIndividuals1Member
2484	Executive officers	Member			tac:ExecutiveOfficer1Member
2485	Non-executive employees	Member			tac:Employee1Member
2486	Disclosure of terms and conditions of share-based payment arrangement [line items]	LineItems			ifrs-full:DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems
2487	Performance period	Concept (xbrli:durationItemType)	For Period		tac:ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod2
2488	Number of performance measures	Concept (Integer)	For Period		tac:ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberofPerformanceMeasures
2489	Vesting period	Concept (xbrli:durationItemType)	For Period		tac:ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod2
2490	Compensation expense (reversal)	Concept (Monetary)	For Period	Debit	ifrs-full:ExpenseFromSharebasedPaymentTransactionsWithEmployees
2491	Number of shares authorized (in shares)	Concept (Shares)	As Of		ifrs-full:SharesReservedForIssueUnderOptionsAndContractsForSaleOfShares
2492	Number of share options granted (in shares)	Concept (Decimal)	For Period		ifrs-full:NumberOfShareOptionsGrantedInSharebasedPaymentArrangement
2493	Exercise price of share options granted (in dollars per share)	Concept (Monetary)	For Period		ifrs-full:WeightedAverageExercisePriceOfShareOptionsGrantedInSharebasedPaymentArrangement
2494	Expiration period of shares granted	Concept (xbrli:durationItemType)	For Period		tac:SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod1
2495	Maximum amount of interest fee loan as percent of employee salary (as percent)	Concept (Percent)	For Period		tac:SharebasedCompensationArrangementbySharebasedPaymentAwardInterestFreeLoanMaximumAmountasPercentageofEmployeeSalary
2496	Repayment period	Concept (xbrli:durationItemType)	For Period		tac:SharebasedCompensationArrangementbySharebasedPaymentAwardInterestFeeLoanTerm
2497	Amount receivable from employees	Concept (Monetary)	As Of	Debit	ifrs-full:TradeAndOtherReceivablesDueFromRelatedParties
2498	2482403 - Disclosure - Share-Based Payment Plans - Stock Options (Details)	Network	*	*	http://www.transalta.com/role/ShareBasedPaymentPlansStockOptionsDetails
2499	Disclosure of number and weighted average remaining contractual life of outstanding share options [table]	Table	*	*	ifrs-full:DisclosureOfNumberAndWeightedAverageRemainingContractualLifeOfOutstandingShareOptionsTable
2500	Ranges of exercise prices for outstanding share options [axis]	Axis			ifrs-full:RangesOfExercisePricesForOutstandingShareOptionsAxis
2501	Ranges of exercise prices for outstanding share options [member]	Member			ifrs-full:RangesOfExercisePricesForOutstandingShareOptionsMember
2502	5.00 - 8.00	Member			tac:ExercisePriceRangeOneMember
2503	22.00 - 30.00	Member			tac:ExercisePriceRangeTwoMember
2504	31.00 - 48.00	Member			tac:ExercisePriceRangeThreeMember
2505	Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]	LineItems			ifrs-full:DisclosureOfNumberAndWeightedAverageRemainingContractualLifeOfOutstandingShareOptionsLineItems
2506	Number of options (in shares)	Concept (Decimal)	As Of		ifrs-full:NumberOfOutstandingShareOptions
2507	Weighted average remaining contractual life (in years)	Concept (xbrli:durationItemType)	For Period		tac:WeightedAverageRemainingContractualLifeOfOutstandingShareOption
2508	Weighted average exercise price (in dollars per share)	Concept (Monetary)	As Of		ifrs-full:WeightedAverageExercisePriceOfShareOptionsOutstandingInSharebasedPaymentArrangement
2509	2482403 - Disclosure - Share-Based Payment Plans - Stock Options (Details)	Network	*	*	http://www.transalta.com/role/ShareBasedPaymentPlansStockOptionsDetails
2510	Disclosure of range of exercise prices of outstanding share options [table]	Table	*	*	ifrs-full:DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsTable
2511	Ranges of exercise prices for outstanding share options [axis]	Axis			ifrs-full:RangesOfExercisePricesForOutstandingShareOptionsAxis
2512	Ranges of exercise prices for outstanding share options [member]	Member			ifrs-full:RangesOfExercisePricesForOutstandingShareOptionsMember
2513	5.00 - 8.00	Member			tac:ExercisePriceRangeOneMember
2514	22.00 - 30.00	Member			tac:ExercisePriceRangeTwoMember
2515	31.00 - 48.00	Member			tac:ExercisePriceRangeThreeMember
2516	Range [axis]	Axis			ifrs-full:RangeAxis
2517	Ranges [member]	Member			ifrs-full:RangesMember
2518	Minimum	Member			ifrs-full:BottomOfRangeMember
2519	Maximum	Member			ifrs-full:TopOfRangeMember
2520	Disclosure of range of exercise prices of outstanding share options [line items]	LineItems			ifrs-full:DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems
2521	Exercise price of outstanding share options (in dollars per share)	Concept (Monetary)	As Of		ifrs-full:ExercisePriceOfOutstandingShareOptions
2522	2485402 - Disclosure - Employee Future Benefits (Details)	Network	*	*	http://www.transalta.com/role/EmployeeFutureBenefitsDetails
2523	Disclosure of defined benefit plans [table]	Table	*	*	ifrs-full:DisclosureOfDefinedBenefitPlansTable
2524	Categories of related parties [axis]	Axis			ifrs-full:CategoriesOfRelatedPartiesAxis
2525	Entity's total for related parties [member]	Member			ifrs-full:EntitysTotalForRelatedPartiesMember
2526	Related parties [member]	Member			ifrs-full:RelatedPartiesMember
2527	Retirement Plan Name [Axis]	Axis			tac:RetirementPlanName1Axis
2528	Retirement Plan Name [Member]	Member			tac:RetirementPlanName1Member
2529	Registered Pension Plan	Member			tac:RegisteredPensionPlanMember
2530	Supplemental Pension Plan	Member			tac:SupplementalPensionPlanMember
2531	Other Post-Employment Benefit Plans	Member			tac:OtherPostEmploymentBenefitPlansMember
2532	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
2533	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
2534	Letter of credit	Member			tac:LetterofCreditMember
2535	Range [axis]	Axis			ifrs-full:RangeAxis
2536	Ranges [member]	Member			ifrs-full:RangesMember
2537	Minimum	Member			ifrs-full:BottomOfRangeMember
2538	Maximum	Member			ifrs-full:TopOfRangeMember
2539	Disclosure of defined benefit plans [line items]	LineItems			ifrs-full:DisclosureOfDefinedBenefitPlansLineItems
2540	Letter of credit, posted	Concept (Monetary)	As Of	Credit	ifrs-full:ExposureToCreditRiskOnLoanCommitmentsAndFinancialGuaranteeContracts
2541	Maximum age disabled and retired members eligible for benefits	Concept (Integer)	For Period		tac:DefinedBenefitPlanMaximumAgeDisabledandRetiredMemberEligibleForBenefits
2542	Employer contribution (as percent)	Concept (Percent)	For Period		tac:DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent1
2543	Administration expenses	Concept (Monetary)	For Period	Credit	tac:AdministrativeExpensesNetDefinedBenefitLiabilityAsset
2544	Weighted average duration of defined benefit obligation	Concept (Decimal)	For Period		ifrs-full:WeightedAverageDurationOfDefinedBenefitObligation
2545	2485403 - Disclosure - Employee Future Benefits - Costs Recognized (Details)	Network	*	*	http://www.transalta.com/role/EmployeeFutureBenefitsCostsRecognizedDetails
2546	Disclosure of net defined benefit liability (asset) [table]	Table	*	*	ifrs-full:DisclosureOfNetDefinedBenefitLiabilityAssetTable
2547	Retirement Plan Name [Axis]	Axis			tac:RetirementPlanName1Axis
2548	Retirement Plan Name [Member]	Member			tac:RetirementPlanName1Member
2549	Registered	Member			tac:RegisteredPensionPlanMember
2550	Supplemental	Member			tac:SupplementalPensionPlanMember
2551	Other	Member			tac:OtherPostEmploymentBenefitPlansMember
2552	Net defined benefit liability (asset) [axis]	Axis			ifrs-full:NetDefinedBenefitLiabilityAssetAxis
2553	Net defined benefit liability (asset) [member]	Member			ifrs-full:NetDefinedBenefitLiabilityAssetMember
2554	Defined benefit obligation	Member			ifrs-full:PresentValueOfDefinedBenefitObligationMember
2555	Plan assets	Member			ifrs-full:PlanAssetsMember
2556	Disclosure of net defined benefit liability (asset) [line items]	LineItems			ifrs-full:DisclosureOfNetDefinedBenefitLiabilityAssetLineItems
2557	Current service cost	Concept (Monetary)	For Period	Credit	ifrs-full:CurrentServiceCostNetDefinedBenefitLiabilityAsset
2558	Administration expenses	Concept (Monetary)	For Period	Credit	tac:AdministrativeExpensesNetDefinedBenefitLiabilityAsset
2559	Interest cost	Concept (Monetary)	For Period	Credit	ifrs-full:InterestExpenseIncomeNetDefinedBenefitLiabilityAsset
2560	Curtailment and amendment gain	Concept (Monetary)	For Period	Debit	tac:CurtailmentandPlanAmendmentGainLossNetDefinedBenefitLiabilityAsset
2561	Defined benefit expense	Concept (Monetary)	For Period	Debit	ifrs-full:PostemploymentBenefitExpenseDefinedBenefitPlans
2562	Defined contribution expense	Concept (Monetary)	For Period	Debit	ifrs-full:PostemploymentBenefitExpenseDefinedContributionPlans
2563	Net expense	Concept (Monetary)	For Period	Debit	ifrs-full:EmployeeBenefitsExpense
2564	2485404 - Disclosure - Employee Future Benefits - Status of Plans (Details)	Network	*	*	http://www.transalta.com/role/EmployeeFutureBenefitsStatusOfPlansDetails
2565	Disclosure of net defined benefit liability (asset) [table]	Table	*	*	ifrs-full:DisclosureOfNetDefinedBenefitLiabilityAssetTable
2566	Retirement Plan Name [Axis]	Axis			tac:RetirementPlanName1Axis
2567	Retirement Plan Name [Member]	Member			tac:RetirementPlanName1Member
2568	Registered	Member			tac:RegisteredPensionPlanMember
2569	Supplemental	Member			tac:SupplementalPensionPlanMember
2570	Other	Member			tac:OtherPostEmploymentBenefitPlansMember
2571	Net defined benefit liability (asset) [axis]	Axis			ifrs-full:NetDefinedBenefitLiabilityAssetAxis
2572	Net defined benefit liability (asset) [member]	Member			ifrs-full:NetDefinedBenefitLiabilityAssetMember
2573	Fair value of plan assets	Member			ifrs-full:PlanAssetsMember
2574	Present value of defined benefit obligation	Member			ifrs-full:PresentValueOfDefinedBenefitObligationMember
2575	Balance Sheet Location [Axis]	Axis			tac:BalanceSheetLocation1Axis
2576	Balance Sheet Location [Member]	Member			tac:BalanceSheetLocation1Member
2577	Accrued current liabilities	Member			tac:AccruedCurrentLiabilitiesMember
2578	Other long-term liabilities	Member			tac:OtherNoncurrentLiabilities1Member
2579	Disclosure of net defined benefit liability (asset) [line items]	LineItems			ifrs-full:DisclosureOfNetDefinedBenefitLiabilityAssetLineItems
2580	Net defined benefit liability (asset)	Concept (Monetary)	As Of	Credit	ifrs-full:LiabilityAssetOfDefinedBenefitPlans
2581	2485405 - Disclosure - Employee Future Benefits - Fair Value of Plan Assets (Details)	Network	*	*	http://www.transalta.com/role/EmployeeFutureBenefitsFairValueOfPlanAssetsDetails
2582	Disclosure of net defined benefit liability (asset) [table]	Table	*	*	ifrs-full:DisclosureOfNetDefinedBenefitLiabilityAssetTable
2583	Retirement Plan Name [Axis]	Axis			tac:RetirementPlanName1Axis
2584	Retirement Plan Name [Member]	Member			tac:RetirementPlanName1Member
2585	Supplemental	Member			tac:SupplementalPensionPlanMember
2586	Registered	Member			tac:RegisteredPensionPlanMember
2587	Other	Member			tac:OtherPostEmploymentBenefitPlansMember
2588	Net defined benefit liability (asset) [axis]	Axis			ifrs-full:NetDefinedBenefitLiabilityAssetAxis
2589	Net defined benefit liability (asset) [member]	Member			ifrs-full:NetDefinedBenefitLiabilityAssetMember
2590	Plan assets	Member			ifrs-full:PlanAssetsMember
2591	Disclosure of net defined benefit liability (asset) [line items]	LineItems			ifrs-full:DisclosureOfNetDefinedBenefitLiabilityAssetLineItems
2592	Net asset, beginning of period	Concept (Monetary)	As Of	Credit	ifrs-full:LiabilityAssetOfDefinedBenefitPlans
2593	Interest on plan assets	Concept (Monetary)	For Period	Credit	ifrs-full:InterestExpenseIncomeNetDefinedBenefitLiabilityAsset
2594	Net return on plan assets	Concept (Monetary)	For Period	Debit	ifrs-full:ReturnOnPlanAssetsNetDefinedBenefitLiabilityAsset
2595	Contributions	Concept (Monetary)	For Period	Debit	ifrs-full:ContributionsToPlanNetDefinedBenefitLiabilityAsset
2596	Benefits paid	Concept (Monetary)	For Period	Debit	ifrs-full:PaymentsInRespectOfSettlementsNetDefinedBenefitLiabilityAsset
2597	Administration expenses	Concept (Monetary)	For Period	Credit	tac:AdministrativeExpensesNetDefinedBenefitLiabilityAsset
2598	Effect of translation on US plans	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughChangesInForeignExchangeRatesNetDefinedBenefitLiabilityAsset
2599	Net asset, ending of period	Concept (Monetary)	As Of	Credit	ifrs-full:LiabilityAssetOfDefinedBenefitPlans
2600	2485406 - Disclosure - Employee Future Benefits - Fair Value of Plan Assets by Major Category (Details)	Network	*	*	http://www.transalta.com/role/EmployeeFutureBenefitsFairValueOfPlanAssetsByMajorCategoryDetails
2601	Disclosure of fair value of plan assets [table]	Table	*	*	ifrs-full:DisclosureOfFairValueOfPlanAssetsTable
2602	Levels of fair value hierarchy [axis]	Axis			ifrs-full:LevelsOfFairValueHierarchyAxis
2603	All levels of fair value hierarchy [member]	Member			ifrs-full:AllLevelsOfFairValueHierarchyMember
2604	Level I	Member			ifrs-full:Level1OfFairValueHierarchyMember
2605	Level II	Member			ifrs-full:Level2OfFairValueHierarchyMember
2606	Level III	Member			ifrs-full:Level3OfFairValueHierarchyMember
2607	External credit grades [axis]	Axis			ifrs-full:ExternalCreditGradesAxis
2608	Entity's total for external credit grades [member]	Member			ifrs-full:EntitysTotalForExternalCreditGradesMember
2609	AAA	Member			tac:AAARatingMember
2610	AA	Member			tac:AARatingMember
2611	A	Member			tac:ARatingMember
2612	BBB	Member			tac:BBBRatingMember
2613	Below BBB	Member			tac:BelowBBBRatingMember
2614	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
2615	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
2616	Country of domicile [member]	Member			ifrs-full:CountryOfDomicileMember
2617	Canadian	Member			country:CA
2618	Foreign countries	Member			ifrs-full:ForeignCountriesMember
2619	US	Member			country:US
2620	International	Member			tac:OtherForeignCountriesMember
2621	Private [Member]	Member			tac:PrivateMember
2622	Disclosure of fair value of plan assets [line items]	LineItems			ifrs-full:DisclosureOfFairValueOfPlanAssetsLineItems
2623	Equity securities	Concept (Monetary)	As Of	Debit	ifrs-full:EquityInstrumentsAmountContributedToFairValueOfPlanAssets
2624	Bonds	Concept (Monetary)	As Of	Debit	ifrs-full:DebtInstrumentsAmountContributedToFairValueOfPlanAssets
2625	Money market and cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalentsAmountContributedToFairValueOfPlanAssets
2626	Total	Concept (Monetary)	As Of	Debit	ifrs-full:PlanAssetsAtFairValue
2627	2485407 - Disclosure - Employee Future Benefits - Defined Benefit Obligation (Details)	Network	*	*	http://www.transalta.com/role/EmployeeFutureBenefitsDefinedBenefitObligationDetails
2628	Disclosure of net defined benefit liability (asset) [table]	Table	*	*	ifrs-full:DisclosureOfNetDefinedBenefitLiabilityAssetTable
2629	Retirement Plan Name [Axis]	Axis			tac:RetirementPlanName1Axis
2630	Retirement Plan Name [Member]	Member			tac:RetirementPlanName1Member
2631	Registered	Member			tac:RegisteredPensionPlanMember
2632	Supplemental	Member			tac:SupplementalPensionPlanMember
2633	Other	Member			tac:OtherPostEmploymentBenefitPlansMember
2634	Net defined benefit liability (asset) [axis]	Axis			ifrs-full:NetDefinedBenefitLiabilityAssetAxis
2635	Net defined benefit liability (asset) [member]	Member			ifrs-full:NetDefinedBenefitLiabilityAssetMember
2636	Present value of defined benefit obligation	Member			ifrs-full:PresentValueOfDefinedBenefitObligationMember
2637	Disclosure of net defined benefit liability (asset) [line items]	LineItems			ifrs-full:DisclosureOfNetDefinedBenefitLiabilityAssetLineItems
2638	Defined benefit obligation, beginning of period	Concept (Monetary)	As Of	Credit	ifrs-full:LiabilityAssetOfDefinedBenefitPlans
2639	Current service cost	Concept (Monetary)	For Period	Credit	ifrs-full:CurrentServiceCostNetDefinedBenefitLiabilityAsset
2640	Interest cost	Concept (Monetary)	For Period	Credit	ifrs-full:InterestExpenseIncomeNetDefinedBenefitLiabilityAsset
2641	Benefits paid	Concept (Monetary)	For Period	Debit	ifrs-full:PaymentsInRespectOfSettlementsNetDefinedBenefitLiabilityAsset
2642	Actuarial gain arising from demographic assumptions	Concept (Monetary)	For Period	Debit	ifrs-full:ActuarialGainsLossesArisingFromChangesInDemographicAssumptionsNetDefinedBenefitLiabilityAsset
2643	Actuarial loss arising from financial assumptions	Concept (Monetary)	For Period	Debit	ifrs-full:ActuarialGainsLossesArisingFromChangesInFinancialAssumptionsNetDefinedBenefitLiabilityAsset
2644	Actuarial gain (loss) arising from experience adjustments	Concept (Monetary)	For Period	Debit	ifrs-full:GainLossOnChangesInEffectOfLimitingNetDefinedBenefitAssetToAssetCeiling
2645	Effect of translation on US plans	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughChangesInForeignExchangeRatesNetDefinedBenefitLiabilityAsset
2646	Defined benefit obligation, ending of period	Concept (Monetary)	As Of	Credit	ifrs-full:LiabilityAssetOfDefinedBenefitPlans
2647	2485408 - Disclosure - Employee Future Benefits - Contributions (Details)	Network	*	*	http://www.transalta.com/role/EmployeeFutureBenefitsContributionsDetails
2648	Disclosure of defined benefit plans [table]	Table	*	*	ifrs-full:DisclosureOfDefinedBenefitPlansTable
2649	Retirement Plan Name [Axis]	Axis			tac:RetirementPlanName1Axis
2650	Retirement Plan Name [Member]	Member			tac:RetirementPlanName1Member
2651	Registered	Member			tac:RegisteredPensionPlanMember
2652	Supplemental	Member			tac:SupplementalPensionPlanMember
2653	Other	Member			tac:OtherPostEmploymentBenefitPlansMember
2654	Disclosure of defined benefit plans [line items]	LineItems			ifrs-full:DisclosureOfDefinedBenefitPlansLineItems
2655	Expected employer contributions	Concept (Monetary)	For Period	Credit	ifrs-full:EstimateOfContributionsExpectedToBePaidToPlan
2656	2485409 - Disclosure - Employee Future Benefits - Assumptions (Details)	Network	*	*	http://www.transalta.com/role/EmployeeFutureBenefitsAssumptionsDetails
2657	Disclosure of defined benefit plans [table]	Table	*	*	ifrs-full:DisclosureOfDefinedBenefitPlansTable
2658	Retirement Plan Type1 [Axis]	Axis			tac:RetirementPlanType1Axis
2659	Retirement Plan Type1 [Domain]	Member			tac:RetirementPlanType1Domain
2660	Accrued Benefit Obligation	Member			tac:AccruedBenefitObligationMember
2661	Other Post-Employment Benefit Plans	Member			tac:OtherPostEmploymentBenefitPlansMember
2662	Retirement Plan Name [Axis]	Axis			tac:RetirementPlanName1Axis
2663	Retirement Plan Name [Member]	Member			tac:RetirementPlanName1Member
2664	Registered	Member			tac:RegisteredPensionPlanMember
2665	Supplemental	Member			tac:SupplementalPensionPlanMember
2666	Other Post-Employment Benefit Plans	Member			tac:OtherPostEmploymentBenefitPlansMember
2667	Other, through 2026	Member			tac:OtherPostEmploymentBenefitPlansthrough2026Member
2668	Other, through 2024	Member			tac:OtherPostEmploymentBenefitPlansthrough2024Member
2669	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
2670	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
2671	US plans	Member			ifrs-full:ForeignDefinedBenefitPlansMember
2672	Canadian plans	Member			ifrs-full:DomesticDefinedBenefitPlansMember
2673	Disclosure of defined benefit plans [line items]	LineItems			ifrs-full:DisclosureOfDefinedBenefitPlansLineItems
2674	Discount rate	Concept (Percent)	As Of		ifrs-full:ActuarialAssumptionOfDiscountRates
2675	Rate of compensation increase	Concept (Percent)	As Of		ifrs-full:ActuarialAssumptionOfExpectedRatesOfSalaryIncreases
2676	Assumed health care cost trend rate	Abstract			tac:ActuarialAssumptionsAbstract
2677	Health care cost escalation(1)(3)	Concept (Percent)	As Of		ifrs-full:ActuarialAssumptionOfMedicalCostTrendRates
2678	Dental care cost escalation	Concept (Percent)	As Of		tac:ActuarialAssumptionOfDentalCostTrendRates
2679	Provincial health care premium escalation	Concept (Percent)	As Of		ifrs-full:ActuarialAssumptionOfExpectedRatesOfInflation
2680	Maximum age disabled and retired members eligible for benefits	Concept (Integer)	For Period		tac:DefinedBenefitPlanMaximumAgeDisabledandRetiredMemberEligibleForBenefits
2681	Percentage of reasonably possible decrease in actuarial assumption	Concept (Percent)	As Of		ifrs-full:PercentageOfReasonablyPossibleDecreaseInActuarialAssumption
2682	2485410 - Disclosure - Employee Future Benefits - Sensitivity Analysis (Details)	Network	*	*	http://www.transalta.com/role/EmployeeFutureBenefitsSensitivityAnalysisDetails
2683	Disclosure of sensitivity analysis for actuarial assumptions [table]	Table	*	*	ifrs-full:DisclosureOfSensitivityAnalysisForActuarialAssumptionsTable
2684	Retirement Plan Name [Axis]	Axis			tac:RetirementPlanName1Axis
2685	Retirement Plan Name [Member]	Member			tac:RetirementPlanName1Member
2686	Registered	Member			tac:RegisteredPensionPlanMember
2687	Supplemental	Member			tac:SupplementalPensionPlanMember
2688	Other	Member			tac:OtherPostEmploymentBenefitPlansMember
2689	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
2690	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
2691	Canadian plans	Member			ifrs-full:DomesticDefinedBenefitPlansMember
2692	US plans	Member			ifrs-full:ForeignDefinedBenefitPlansMember
2693	Actuarial assumptions [axis]	Axis			ifrs-full:ActuarialAssumptionsAxis
2694	Actuarial assumptions [member]	Member			ifrs-full:ActuarialAssumptionsMember
2695	1% decrease in the discount rate	Member			ifrs-full:ActuarialAssumptionOfDiscountRatesMember
2696	1% increase in the salary scale	Member			ifrs-full:ActuarialAssumptionOfExpectedRatesOfSalaryIncreasesMember
2697	1% increase in the health care cost trend rate	Member			ifrs-full:ActuarialAssumptionOfMedicalCostTrendRatesMember
2698	10% improvement in mortality rates	Member			ifrs-full:ActuarialAssumptionOfMortalityRatesMember
2699	Disclosure of sensitivity analysis for actuarial assumptions [line items]	LineItems			ifrs-full:DisclosureOfSensitivityAnalysisForActuarialAssumptionsLineItems
2700	Increase in defined benefit obligation	Concept (Monetary)	As Of	Credit	ifrs-full:IncreaseDecreaseInDefinedBenefitObligationDueToReasonablyPossibleIncreaseInActuarialAssumption
2701	Percentage of reasonably possible increase in actuarial assumption (as percent)	Concept (Percent)	As Of		ifrs-full:PercentageOfReasonablyPossibleIncreaseInActuarialAssumption
2702	2488402 - Disclosure - Joint Arrangements (Details)	Network	*	*	http://www.transalta.com/role/JointArrangementsDetails
2703	Disclosure of joint operations [table]	Table	*	*	ifrs-full:DisclosureOfJointOperationsTable
2704	Joint operations [axis]	Axis			ifrs-full:JointOperationsAxis
2705	Entity's total for joint operations [member]	Member			ifrs-full:EntitysTotalForJointOperationsMember
2706	Sheerness	Member			tac:SheernessMember
2707	Genesee Unit 3	Member			tac:GeneseeUnit3Member
2708	Keephills Unit 3	Member			tac:KeephillsUnit3Member
2709	Goldfields Power	Member			tac:GoldfieldsPowerMember
2710	Fort Saskatchewan	Member			tac:FortSaskatchewanMember
2711	Fortescue River Gas Pipeline	Member			tac:FortescueRiverGasPipelineMember
2712	Wintering Hills	Member			tac:WinteringHillsMember
2713	McBride Lake	Member			tac:McBrideLakeMember
2714	Soderglen	Member			tac:SoderglenMember
2715	Pingston	Member			tac:PingstonMember
2716	Segments [axis]	Axis			ifrs-full:SegmentsAxis
2717	Segments [member]	Member			ifrs-full:SegmentsMember
2718	Coal generation	Member			tac:CoalGenerationMember
2719	Gas generation	Member			tac:GasGenerationMember
2720	Wind Generation	Member			tac:WindGenerationMember
2721	Hydro	Member			tac:HydroGenerationMember
2722	Disclosure of joint operations [line items]	LineItems			ifrs-full:DisclosureOfJointOperationsLineItems
2723	Proportion of ownership interest in joint operation	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInJointOperation
2724	2491402 - Disclosure - Cash Flow Information (Details)	Network	*	*	http://www.transalta.com/role/CashFlowInformationDetails
2725	Implied Table	Table	*	*	implied:Table
2726	Cash flows from (used in) operating activities [abstract]	Abstract			ifrs-full:CashFlowsFromUsedInOperatingActivitiesAbstract
2727	Accounts receivable	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDecreaseIncreaseInTradeAccountReceivable
2728	Prepaid expenses	Concept (Monetary)	For Period	Debit	tac:Adjustmentsforincreasedecreaseinprepaidexpenses
2729	Income taxes receivable	Concept (Monetary)	For Period	Debit	tac:Adjustmentsforincometaxreceivable
2730	Inventory	Concept (Monetary)	For Period	Debit	tac:Adjustmentsfordecreaseincreaseininventory
2731	Accounts payable, accrued liabilities, and provisions	Concept (Monetary)	For Period	Debit	tac:Adjustmentsforincreasedecreaseinaccountspayableandothercurrentliabilities
2732	Income taxes payable	Concept (Monetary)	For Period	Credit	tac:Adjustmentsforincometaxpayable
2733	Change in non-cash operating working capital	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseInWorkingCapital
2734	2491403 - Disclosure - Cash Flow Information Changes in Liabilities from Financing Activities (Details)	Network	*	*	http://www.transalta.com/role/CashFlowInformationChangesInLiabilitiesFromFinancingActivitiesDetails
2735	Disclosure of reconciliation of liabilities arising from financing activities [table]	Table	*	*	ifrs-full:DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesTable
2736	Liabilities arising from financing activities [axis]	Axis			ifrs-full:LiabilitiesArisingFromFinancingActivitiesAxis
2737	Liabilities arising from financing activities [member]	Member			ifrs-full:LiabilitiesArisingFromFinancingActivitiesMember
2738	Long-term debt and finance lease obligations	Member			ifrs-full:LongtermBorrowingsMember
2739	Dividends payable (common and preferred)	Member			tac:DividendsPayable1Member
2740	Disclosure of reconciliation of liabilities arising from financing activities [line items]	LineItems			ifrs-full:DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems
2741	Balance at beginning of the period	Concept (Monetary)	As Of	Credit	ifrs-full:LiabilitiesArisingFromFinancingActivities
2742	Net cash flows	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughFinancingCashFlowsLiabilitiesArisingFromFinancingActivities
2743	New leases	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseThroughNewLeasesLiabilitiesArisingFromFinancingActivities
2744	Dividends declared	Concept (Monetary)	For Period	Credit	tac:IncreaseDecreaseThroughDividendsDeclaredLiabilitiesArisingFromFinancingActivities
2745	Foreign exchange impact	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughEffectOfChangesInForeignExchangeRatesLiabilitiesArisingFromFinancingActivities
2746	Other	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughOtherChangesLiabilitiesArisingFromFinancingActivities
2747	Balance at end of the period	Concept (Monetary)	As Of	Credit	ifrs-full:LiabilitiesArisingFromFinancingActivities
2748	2494402 - Disclosure - Capital Disclosure of components of capital (Details)	Network	*	*	http://www.transalta.com/role/CapitalDisclosureOfComponentsOfCapitalDetails
2749	Disclosure of components of capital [Table]	Table	*	*	tac:DisclosureofcomponentsofcapitalTable
2750	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
2751	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
2752	TransAlta OCP	Member			tac:TransAltaOCPMember
2753	Components of equity [axis]	Axis			ifrs-full:ComponentsOfEquityAxis
2754	Equity [member]	Member			ifrs-full:EquityMember
2755	Common shares	Member			tac:CommonsharesMember
2756	Preferred shares	Member			ifrs-full:PreferenceSharesMember
2757	Contributed surplus	Member			ifrs-full:AdditionalPaidinCapitalMember
2758	Deficit	Member			ifrs-full:RetainedEarningsMember
2759	Accumulated other comprehensive income	Member			ifrs-full:AccumulatedOtherComprehensiveIncomeMember
2760	Non-controlling interests	Member			ifrs-full:NoncontrollingInterestsMember
2761	Disclosure of components of capital [Line Items]	LineItems			tac:DisclosureofcomponentsofcapitalLineItems
2762	Long-term debt	Concept (Monetary)	As Of	Credit	ifrs-full:FinancialLiabilities
2763	Increase (decrease) in financial liabilities	Concept (Monetary)	For Period	Credit	tac:Increasedecreaseinfinancialliabilities
2764	Issued capital (Note 24)	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
2765	Increase (decrease) in issued capital	Concept (Monetary)	For Period	Credit	tac:Increasedecreaseinissuedcapital
2766	Equity	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
2767	Increase (decrease) in equity	Concept (Monetary)	For Period	Credit	ifrs-full:ChangesInEquity
2768	Preferred shares	Concept (Monetary)	As Of	Credit	tac:IssuedPreferredCapital
2769	Contributed surplus	Concept (Monetary)	As Of	Credit	ifrs-full:AdditionalPaidinCapital
2770	Deficit	Concept (Monetary)	As Of	Credit	ifrs-full:RetainedEarnings
2771	Accumulated other comprehensive income	Concept (Monetary)	As Of	Credit	ifrs-full:AccumulatedOtherComprehensiveIncome
2772	Non-controlling interests	Concept (Monetary)	As Of	Credit	ifrs-full:NoncontrollingInterests
2773	Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
2774	Increase (decrease) in cash and cash equivalents	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseInCashAndCashEquivalents
2775	Current restricted cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentRestrictedCashAndCashEquivalents
2776	Increase (decrease) in restricted cash and cash equivalents	Concept (Monetary)	For Period	Debit	tac:IncreaseDecreaseInRestrictedCashAndCashEquivalents
2777	Fair value asset of hedging instruments on long-term debt	Concept (Monetary)	As Of	Debit	ifrs-full:HedgingInstrumentAssets
2778	Increase (decrease) in hedging instruments, liabilities	Concept (Monetary)	For Period	Debit	tac:Increasedecreaseinhedginginstrumentsassets
2779	Total capital	Concept (Monetary)	As Of	Credit	tac:Capital1
2780	Increase (decrease) in capital	Concept (Monetary)	For Period	Credit	tac:Increasedecreaseincapital
2781	2494403 - Disclosure - Capital Disclosure of investment grade credit rating (Details)	Network	*	*	http://www.transalta.com/role/CapitalDisclosureOfInvestmentGradeCreditRatingDetails
2782	Investment [Table]	Table	*	*	invest:InvestmentTable
2783	Range [axis]	Axis			ifrs-full:RangeAxis
2784	Ranges [member]	Member			ifrs-full:RangesMember
2785	Minimum	Member			ifrs-full:BottomOfRangeMember
2786	Maximum	Member			ifrs-full:TopOfRangeMember
2787	Investment [Line Items]	LineItems			invest:InvestmentLineItems
2788	Comparable funds from operations to adjusted interest coverage, actual	Concept (Pure)	For Period		tac:Comparablefundsfromoperationsbeforeinteresttoadjustedinterestcoverageactual
2789	Adjusted comparable funds from operations to adjusted net debt, actual	Concept (Percent)	For Period		tac:Adjustedcomparablefundsoperationstoadjustednetdebtactual
2790	Adjusted net debt to comparable earnings before interest, taxes, depreciation, and amortization, actual	Concept (Pure)	For Period		tac:Adjustednetdebttocomparableearningsbeforeinteresttaxesdepreciationandamortizationactual
2791	Comparable funds from operations to adjusted interest coverage, Target	Concept (Pure)	For Period		tac:Comparablefundsfromoperationsbeforeinteresttoadjustedinterestcoveragetarget
2792	Adjusted comparable funds from operations to adjusted net debt, Target	Concept (Pure)	For Period		tac:Adjustedcomparablefundsoperationstoadjustednetdebttarget
2793	Adjusted net debt to comparable earnings before interest, taxes, depreciation, and amortization, Target	Concept (Pure)	For Period		tac:Adjustednetdebttocomparableearningsbeforeinteresttaxesdepreciationandamortizationtarget
2794	Percentage of dividends added to Comparable FFO before Interest to Adjusted Interest Coverage	Concept (Percent)	For Period		tac:PercentageofdividendsaddedtoComparableFundsFromOperationsbeforeInteresttoAdjustedInterestCoverageRatio
2795	Percentage of preferred dividends deducted from Adjusted Comparable FFO to Adjusted Net Debt	Concept (Percent)	For Period		tac:PercentageofpreferreddividendsdeductedfromAdjustedComparableFundsFromOperationstoAdjustedNetDebtRatio
2796	Percentage of preferred shares added to net debt in Adjusted Comparable FFO to Adjusted Net Debt	Concept (Percent)	For Period		tac:PercentageofpreferredsharesaddedtonetdebtinAdjustedComparableFundsFromOperationstoAdjustedNetDebtRatio
2797	Annual dividend per share	Concept (Share)	As Of		tac:AnnualDividendPerShare
2798	2494404 - Disclosure - Capital Disclosure of cash flow statement (Details)	Network	*	*	http://www.transalta.com/role/CapitalDisclosureOfCashFlowStatementDetails
2799	Disclosure of classes of share capital [table]	Table	*	*	ifrs-full:DisclosureOfClassesOfShareCapitalTable
2800	Classes of share capital [axis]	Axis			ifrs-full:ClassesOfShareCapitalAxis
2801	Share capital [member]	Member			ifrs-full:ClassesOfShareCapitalMember
2802	Common shares	Member			tac:CommonsharesMember
2803	Preferred shares	Member			ifrs-full:PreferenceSharesMember
2804	Disclosure of classes of share capital [line items]	LineItems			ifrs-full:DisclosureOfClassesOfShareCapitalLineItems
2805	Cash flows from (used in) operating activities	Concept (Monetary)	For Period		ifrs-full:CashFlowsFromUsedInOperatingActivities
2806	Increase (decrease) in cash flow from (used in) operating activities	Concept (Monetary)	For Period	Credit	tac:Increasedecreaseincashflowfromusedinoperatingactivities
2807	Change in non-cash operating working capital balances	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseInWorkingCapital
2808	Increase (decrease) in non cash working capital	Concept (Monetary)	For Period	Credit	tac:IncreaseDecreaseInNonCashWorkingCapital
2809	Cash flow from operations before changes in working capital	Concept (Monetary)	For Period		ifrs-full:CashFlowsFromUsedInOperationsBeforeChangesInWorkingCapital
2810	Increase (decrease) in cash flow from operations before changes in working capital	Concept (Monetary)	For Period	Credit	tac:Increasedecreaseincashflowfromoperationsbeforechangesinworkingcapital
2811	Dividends paid	Concept (Monetary)	For Period	Credit	ifrs-full:DividendsPaidClassifiedAsFinancingActivities
2812	Increase (decrease) in dividends paid	Concept (Monetary)	For Period	Credit	tac:Increasedecreaseindividendspaid
2813	Distributions paid to subsidiaries� non-controlling interests	Concept (Monetary)	For Period	Credit	ifrs-full:DividendsPaidToNoncontrollingInterestsClassifiedAsFinancingActivities
2814	Increase (decrease) in dividends paid to non controlling interests	Concept (Monetary)	For Period	Credit	tac:Increasedecreaseindividendspaidtononcontrollinginterests
2815	Property, plant and equipment expenditures	Concept (Monetary)	For Period	Credit	ifrs-full:PurchaseOfPropertyPlantAndEquipmentClassifiedAsInvestingActivities
2816	Increase (decrease) in property, plant and equipment expenditure	Concept (Monetary)	For Period	Credit	tac:Increasedecreaseinpropertyplantandequipmentexpenditure
2817	Net inflows (outflows) of cash	Concept (Monetary)	For Period	Debit	tac:Netcapitalinflowsoutflows
2818	Increase (decrease) in net inflows (outflows) of cash	Concept (Monetary)	For Period	Credit	tac:Increasedecreaseinnetcapitalinflowsoutflows
2819	Undrawn credit facilities	Concept (Monetary)	As Of	Credit	tac:Undrawncreditfacilities
2820	2497402 - Disclosure - Related Party Transactions Disclosure of interests in subsidiaries (Details)	Network	*	*	http://www.transalta.com/role/RelatedPartyTransactionsDisclosureOfInterestsInSubsidiariesDetails
2821	Disclosure of subsidiaries [table]	Table	*	*	ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesTable
2822	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
2823	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
2824	Canada	Member			country:CA
2825	UNITED STATES	Member			country:US
2826	Australia	Member			country:AU
2827	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
2828	Subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
2829	TransAlta Generation Partnership [Member]	Member			tac:TransAltaGenerationPartnershipMember
2830	TransAlta Cogeneration L.P.	Member			tac:TransAltaCogenerationL.P.Member
2831	TransAlta Centralia Generation, LLC [Member]	Member			tac:TransAltaCentraliaGenerationLLCMember
2832	TransAlta Energy Marketing Corp [Member]	Member			tac:TransAltaEnergyMarketingCorpMember
2833	TransAlta Energy Marketing (U.S.), Inc [Member]	Member			tac:TransAltaEnergyMarketingU.S.IncMember
2834	TransAlta Energy (Australia). Ptv Ltd [Member]	Member			tac:TransAltaEnergyAustralia.PtvLtdMember
2835	TransAlta Renewables	Member			tac:TransAltaRenewablesInc.Member
2836	Disclosure of subsidiaries [line items]	LineItems			ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesLineItems
2837	Ownership interest (as a percent)	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInSubsidiary
2838	2497403 - Disclosure - Related Party Transactions Disclosure of transactions between related parties (Details)	Network	*	*	http://www.transalta.com/role/RelatedPartyTransactionsDisclosureOfTransactionsBetweenRelatedPartiesDetails
2839	Implied Table	Table	*	*	implied:Table
2840	Related Party [Abstract]	Abstract			tac:RelatedPartyAbstract
2841	Total compensation	Concept (Monetary)	For Period	Debit	ifrs-full:KeyManagementPersonnelCompensation
2842	Short-term employee benefits	Concept (Monetary)	For Period	Debit	ifrs-full:KeyManagementPersonnelCompensationShorttermEmployeeBenefits
2843	Post-employment benefits	Concept (Monetary)	For Period	Debit	ifrs-full:KeyManagementPersonnelCompensationPostemploymentBenefits
2844	Termination benefits	Concept (Monetary)	For Period	Debit	ifrs-full:KeyManagementPersonnelCompensationTerminationBenefits
2845	Share-based payments	Concept (Monetary)	For Period	Debit	ifrs-full:KeyManagementPersonnelCompensationSharebasedPayment
2846	2498402 - Disclosure - Commitments and Contingencies - Commitments (Details)	Network	*	*	http://www.transalta.com/role/CommitmentsAndContingenciesCommitmentsDetails
2847	Disclosure of Commitments [Table]	Table	*	*	tac:DisclosureofCommitmentsTable
2848	Types of investment property [axis]	Axis			ifrs-full:TypesOfInvestmentPropertyAxis
2849	Investment property [member]	Member			ifrs-full:InvestmentPropertyMember
2850	Tidewater Brazeau River Pipeline	Member			tac:TidewaterBrazeauRiverPipelineMember
2851	Counterparties [axis]	Axis			ifrs-full:CounterpartiesAxis
2852	Counterparties [member]	Member			ifrs-full:CounterpartiesMember
2853	Tidewater	Member			tac:TidewaterMidstreamandInfrastructureLtdMember
2854	Classes of other provisions [axis]	Axis			ifrs-full:ClassesOfProvisionsAxis
2855	Other provisions [member]	Member			ifrs-full:OtherProvisionsMember
2856	Line loss rule proceeding	Member			ifrs-full:LegalProceedingsProvisionMember
2857	Maturity [axis]	Axis			ifrs-full:MaturityAxis
2858	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
2859	2018	Member			ifrs-full:NotLaterThanOneYearMember
2860	2019	Member			ifrs-full:LaterThanOneYearAndNotLaterThanTwoYearsMember
2861	2020	Member			ifrs-full:LaterThanTwoYearsAndNotLaterThanThreeYearsMember
2862	2021	Member			ifrs-full:LaterThanThreeYearsAndNotLaterThanFourYearsMember
2863	2022	Member			ifrs-full:LaterThanFourYearsAndNotLaterThanFiveYearsMember
2864	2023 and thereafter	Member			ifrs-full:LaterThanFiveYearsMember
2865	Purchase Obligation Item [axis]	Axis			tac:PurchaseObligationItemAxis
2866	Purchase Obligation Item [Member]	Member			tac:PurchaseObligationItemMember
2867	Natural gas, transportation and other purchase contracts	Member			tac:NaturalGasTransportationandOtherProductsandServicesMember
2868	Transmission	Member			tac:TransmissionNetworkCapacityMember
2869	Disclosure of Commitments [Line Items]	LineItems			tac:DisclosureofCommitmentsLineItems
2870	Purchase obligations	Concept (Monetary)	As Of	Credit	tac:PurchaseObligations1
2871	Coal supply and mining agreements	Concept (Monetary)	As Of	Credit	tac:CoalSupplyandMiningObligation
2872	Long-term service agreements	Concept (Monetary)	As Of	Credit	tac:LongtermServiceObligation
2873	Non-cancellable operating leases	Concept (Monetary)	As Of	Credit	ifrs-full:MinimumLeasePaymentsPayableUnderNoncancellableOperatingLease
2874	Growth	Concept (Monetary)	As Of	Credit	ifrs-full:ContractualCapitalCommitments
2875	TransAlta Energy Transition Bill	Concept (Monetary)	As Of	Credit	tac:CommitmentforEnergyBillInitiatives
2876	Total	Concept (Monetary)	As Of	Credit	tac:ContractualObligations1
2877	Minimum operating lease payments recognised as expense	Concept (Monetary)	For Period	Debit	ifrs-full:MinimumOperatingLeasePayments
2878	Sublease payments received (amounts less than)	Concept (Monetary)	For Period	Credit	ifrs-full:IncomeFromSubleasingRightofuseAssets
2879	Future option to acquire pipeline, ownership percentage	Concept (Percent)	As Of		tac:OptiontoAcquirePipelineOwnershipPercentage
2880	Commitment period for Energy Bill initiatives	Concept (xbrli:durationItemType)	For Period		tac:CommitmentPeriodforEnergyBillInitiatives
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2882	Estimated financial effect of contingent liabilities	Concept (Monetary)	As Of	Credit	tac:ContingentLiabilitiesMaximumExposure
2883	Provision for line loss rule proceeding	Concept (Monetary)	For Period	Credit	ifrs-full:AdditionalProvisionsOtherProvisions
2884	Amount withheld under dispute	Concept (Monetary)	As Of	Debit	tac:AmountWithheldUnderLitigationDispute
2885	Amount withheld under dispute, tax	Concept (Monetary)	As Of	Debit	tac:AmountWithheldUnderLitigationDisputeTax
2886	Pending litigation claim	Concept (Monetary)	As Of	Debit	tac:Pendinglitigationclaim
2887	Number Of legal disputes	Concept (Integer)	For Period		tac:NumberOfLegalDisputes
2888	Litigation settlement, amount awarded from other party	Concept (Monetary)	For Period	Debit	tac:LitigationSettlementAmountAwardedFromOtherParty1
2889	Mining assets	Concept (Monetary)	As Of	Debit	ifrs-full:MiningAssets
2890	2498402 - Disclosure - Segment Disclosures Disclosure of operating segments (Details)	Network	*	*	http://www.transalta.com/role/SegmentDisclosuresDisclosureOfOperatingSegmentsDetails
2891	Disclosure of operating segments [table]	Table	*	*	ifrs-full:DisclosureOfOperatingSegmentsTable
2892	Segments [axis]	Axis			ifrs-full:SegmentsAxis
2893	Segments [member]	Member			ifrs-full:SegmentsMember
2894	Reportable segments [member]	Member			ifrs-full:ReportableSegmentsMember
2895	Segment consolidation items [axis]	Axis			ifrs-full:SegmentConsolidationItemsAxis
2896	Entity's total for segment consolidation items [member]	Member			ifrs-full:EntitysTotalForSegmentConsolidationItemsMember
2897	Canadian Coal	Member			tac:CanadianCoalMember
2898	United States Coal	Member			tac:UnitedStatesCoalMember
2899	Canadian Gas	Member			tac:CanadianGasMember
2900	Australian Gas	Member			tac:AustralianGasMember
2901	Wind and Solar	Member			tac:WindandSolarMember
2902	Hydro	Member			tac:HydroMember
2903	Energy Marketing	Member			tac:EnergyMarketingMember
2904	Corporate	Member			tac:Corporate1Member
2905	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
2906	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
2907	Canada	Member			country:CA
2908	US	Member			country:US
2909	Australia	Member			country:AU
2910	Disclosure of operating segments [line items]	LineItems			ifrs-full:DisclosureOfOperatingSegmentsLineItems
2911	Revenues	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
2912	Fuel and purchased power (Note 6)	Concept (Monetary)	For Period	Debit	ifrs-full:CostOfSales
2913	Gross margin	Concept (Monetary)	For Period	Credit	ifrs-full:GrossProfit
2914	Operations, maintenance, and administration (Note 5)	Concept (Monetary)	For Period	Debit	tac:OperationsMaintenanceAndAdministrativeExpense
2915	Depreciation and amortization	Concept (Monetary)	For Period	Debit	ifrs-full:DepreciationAndAmortisationExpense
2916	Asset impairment charges (reversals) (Note 7)	Concept (Monetary)	For Period	Debit	ifrs-full:ImpairmentLossReversalOfImpairmentLossRecognisedInProfitOrLoss
2917	Restructuring provision	Concept (Monetary)	For Period	Debit	ifrs-full:ExpenseOfRestructuringActivities
2918	Taxes, other than income taxes	Concept (Monetary)	For Period	Debit	ifrs-full:TaxExpenseOtherThanIncomeTaxExpense
2919	Profit (loss) from operating activities	Concept (Monetary)	For Period	Debit	ifrs-full:OtherAdjustmentsToReconcileProfitLoss
2920	Operating income	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueAndOperatingIncome
2921	Finance lease income	Concept (Monetary)	For Period	Credit	ifrs-full:FinanceIncomeOnNetInvestmentInFinanceLease
2922	Gain on sale of assets and other	Concept (Monetary)	For Period	Credit	ifrs-full:GainsOnDisposalsOfNoncurrentAssets
2923	Net interest expense (Note 10)	Concept (Monetary)	For Period	Debit	ifrs-full:InterestExpense
2924	Foreign exchange gain (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnExchangeDifferencesOnTranslationRecognisedInProfitOrLoss
2925	Earnings (loss) before income taxes	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossBeforeTax
2926	Income from government grants	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromGovernmentGrants
2927	Contingent rents recognised as income, classified as operating lease	Concept (Monetary)	For Period	Credit	ifrs-full:ContingentRentsRecognisedAsIncomeClassifiedAsOperatingLease
2928	Goodwill (Note 18)	Concept (Monetary)	As Of	Debit	ifrs-full:Goodwill
2929	Property, plant and equipment (Note 17)	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
2930	Intangible assets (Note 19)	Concept (Monetary)	As Of	Debit	ifrs-full:IntangibleAssetsOtherThanGoodwill
2931	Other assets (Note 20)	Concept (Monetary)	As Of	Debit	ifrs-full:OtherNoncurrentAssets
2932	Property, plant and equipment expenditures	Concept (Monetary)	For Period	Credit	ifrs-full:PurchaseOfPropertyPlantAndEquipmentClassifiedAsInvestingActivities
2933	Purchase of intangible assets	Concept (Monetary)	For Period	Credit	ifrs-full:PurchaseOfIntangibleAssetsClassifiedAsInvestingActivities
2934	Mine depreciation	Concept (Monetary)	For Period	Debit	ifrs-full:DepreciationExpense
2935	Loss on disposal of property, plant, and equipment	Concept (Monetary)	For Period	Debit	ifrs-full:LossesOnDisposalsOfPropertyPlantAndEquipment
2936	Adjustments for depreciation and amortisation expense	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDepreciationAndAmortisationExpense
2937	2498403 - Disclosure - Segment Disclosures Disclosure of entity's operating segments (Details)	Network	*	*	http://www.transalta.com/role/SegmentDisclosuresDisclosureOfEntitysOperatingSegmentsDetails
2938	Disclosure of major customers [table]	Table	*	*	ifrs-full:DisclosureOfMajorCustomersTable
2939	Major customers [axis]	Axis			ifrs-full:MajorCustomersAxis
2940	Customers [member]	Member			ifrs-full:MajorCustomersMember
2941	Customer 1	Member			tac:Customer1Member
2942	Customer 2	Member			tac:Customer2Member
2943	Disclosure of major customers [line items]	LineItems			ifrs-full:DisclosureOfMajorCustomersLineItems
2944	Number of segments	Concept (Integer)	As Of		tac:NumberOfReportableSegments1
2945	Percentage of entity's revenue	Concept (Percent)	For Period		ifrs-full:PercentageOfEntitysRevenue