CNOOC LTD (SEC Filing Page | XBRL Cloud Viewer | XBRL Instance)

Line	Label	Object Class	Period Type	Balance	Report ElementName
1	00090 - Document - DOCUMENT AND ENTITY INFORMATION	Network	*	*	http://www.cnoocltd.com/role/DocumentAndEntityInformation
2	Implied Table	Table	*	*	implied:Table
3	Document and Entity Information [abstract]	Abstract			ceo:DocumentAndEntityInformationAbstract
4	Entity Registrant Name	Concept (Text/String)	For Period		dei:EntityRegistrantName
5	Entity Central Index Key	Concept (CIK Number)	For Period		dei:EntityCentralIndexKey
6	Document Type	Concept (Submission Type)	For Period		dei:DocumentType
7	Document Period End Date	Concept (Date)	For Period		dei:DocumentPeriodEndDate
8	Amendment Flag	Concept (Yes/No)	For Period		dei:AmendmentFlag
9	Current Fiscal Year End Date	Concept (Month/Day)	For Period		dei:CurrentFiscalYearEndDate
10	Entity Well-known Seasoned Issuer	Concept (Yes/No)	For Period		dei:EntityWellKnownSeasonedIssuer
11	Entity Voluntary Filers	Concept (Yes/No)	For Period		dei:EntityVoluntaryFilers
12	Entity Current Reporting Status	Concept (Yes/No)	For Period		dei:EntityCurrentReportingStatus
13	Entity Filer Category	Concept (Filer Category)	For Period		dei:EntityFilerCategory
14	Entity Common Stock, Shares Outstanding	Concept (Shares)	As Of		dei:EntityCommonStockSharesOutstanding
15	Entity Emerging Growth Company	Concept (Yes/No)	For Period		dei:EntityEmergingGrowthCompany
16	Entity Shell Company	Concept (Yes/No)	For Period		dei:EntityShellCompany
17	Document Fiscal Year Focus	Concept (Year)	For Period		dei:DocumentFiscalYearFocus
18	Document Fiscal Period Focus	Concept (Fiscal Period)	For Period		dei:DocumentFiscalPeriodFocus
19	00100 - Statement - CONSOLIDATED STATEMENTS OF PROFIT OR LOSS AND OTHER COMPREHENSIVE INCOME	Network	*	*	http://www.cnoocltd.com/role/ConsolidatedStatementsOfProfitOrLossAndOtherComprehensiveIncome
20	Implied Table	Table	*	*	implied:Table
21	CONSOLIDATED STATEMENTS OF PROFIT OR LOSS AND OTHER COMPREHENSIVE INCOME [abstract]	Abstract			ifrs-full:StatementOfComprehensiveIncomeAbstract
22	REVENUE [abstract]	Abstract			ifrs-full:RevenueAbstract
23	Revenue recognized from contracts with customers	Abstract			ceo:RevenueRecognizedFromContractsWithCustomersAbstract
24	Oil and gas sales	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromSaleOfOilAndGasProducts
25	Marketing revenues	Concept (Monetary)	For Period	Credit	ceo:RevenueFromMarketing
26	Other revenue	Concept (Monetary)	For Period	Credit	ifrs-full:OtherRevenue
27	Total revenue	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
28	EXPENSES [abstract]	Abstract			ifrs-full:ExpenseByNatureAbstract
29	Operating expenses	Concept (Monetary)	For Period	Debit	ifrs-full:OperatingExpense
30	Taxes other than income tax	Concept (Monetary)	For Period	Debit	ifrs-full:TaxExpenseOtherThanIncomeTaxExpense
31	Exploration expenses	Concept (Monetary)	For Period	Debit	ifrs-full:ExpenseArisingFromExplorationForAndEvaluationOfMineralResources
32	Depreciation, depletion and amortization	Concept (Monetary)	For Period	Debit	ifrs-full:DepreciationAndAmortisationExpense
33	Special oil gain levy	Concept (Monetary)	For Period	Debit	ceo:SpecialOilGainLevyExpense
34	Impairment and provision	Concept (Monetary)	For Period	Debit	ifrs-full:ImpairmentLossRecognisedInProfitOrLoss
35	Crude oil and product purchases	Concept (Monetary)	For Period	Debit	ceo:PurchaseOfCrudeOilAndProduct
36	Selling and administrative expenses	Concept (Monetary)	For Period	Debit	ifrs-full:SellingGeneralAndAdministrativeExpense
37	Others	Concept (Monetary)	For Period	Debit	ifrs-full:OtherExpenseByNature
38	Total expenses	Concept (Monetary)	For Period	Debit	ifrs-full:ExpenseByNature
39	(LOSS)/PROFIT FROM OPERATING ACTIVITIES	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossFromOperatingActivities
40	Interest income	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromInterest
41	Finance costs	Concept (Monetary)	For Period	Debit	ifrs-full:FinanceCosts
42	Exchange (losses)/gains, net	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnExchangeDifferencesOnTranslationBeforeTax
43	Investment income	Concept (Monetary)	For Period	Credit	ifrs-full:InvestmentIncome
44	Share of (losses)/profits of associates	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfProfitLossOfAssociatesAccountedForUsingEquityMethod
45	Profit/(loss) attributable to a joint venture	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfProfitLossOfJointVenturesAccountedForUsingEquityMethod
46	Other income, net	Concept (Monetary)	For Period	Credit	ifrs-full:OtherIncome
47	(LOSS)/PROFIT BEFORE TAX	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossBeforeTax
48	Income tax credit/(expense)	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
49	PROFIT FOR THE YEAR ATTRIBUTABLE TO OWNERS OF THE PARENT	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossAttributableToOwnersOfParent
50	OTHER COMPREHENSIVE INCOME/(EXPENSE) [abstract]	Abstract			ifrs-full:OtherComprehensiveIncomeAbstract
51	Items that may be subsequently reclassified to profit or loss	Abstract			ifrs-full:ComponentsOfOtherComprehensiveIncomeThatWillBeReclassifiedToProfitOrLossNetOfTaxAbstract
52	Exchange differences on translation of foreign operations	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeNetOfTaxExchangeDifferencesOnTranslation
53	Share of other comprehensive (expense)/income of associates	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfOtherComprehensiveIncomeOfAssociatesAndJointVenturesAccountedForUsingEquityMethodThatWillBeReclassifiedToProfitOrLossNetOfTax
54	Other items that will not be reclassified to profit or loss	Abstract			ifrs-full:ComponentsOfOtherComprehensiveIncomeThatWillNotBeReclassifiedToProfitOrLossNetOfTaxAbstract
55	Fair value change on equity investments designated as at fair value through other comprehensive (expense)/income	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeNetOfTaxGainsLossesFromInvestmentsInEquityInstruments
56	Others	Concept (Monetary)	For Period	Credit	ceo:OtherComprehensiveIncomeThatWillNotBeReclassifiedToProfitOrLossOthers
57	OTHER COMPREHENSIVE INCOME/(EXPENSE) FOR THE YEAR, NET OF TAX	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncome
58	TOTAL COMPREHENSIVE INCOME FOR THE YEAR ATTRIBUTABLE TO OWNERS OF THE PARENT	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncomeAttributableToOwnersOfParent
59	EARNINGS PER SHARE ATTRIBUTABLE TO OWNERS OF THE PARENT [abstract]	Abstract			ifrs-full:BasicAndDilutedEarningsPerShareAbstract
60	Basic (RMB Yuan)	Concept (Share)	For Period		ifrs-full:BasicEarningsLossPerShare
61	Diluted (RMB Yuan)	Concept (Share)	For Period		ifrs-full:DilutedEarningsLossPerShare
62	00200 - Statement - CONSOLIDATED STATEMENTS OF FINANCIAL POSITION	Network	*	*	http://www.cnoocltd.com/role/ConsolidatedStatementsOfFinancialPosition
63	Implied Table	Table	*	*	implied:Table
64	CONSOLIDATED STATEMENTS OF FINANCIAL POSITION [abstract]	Abstract			ifrs-full:StatementOfFinancialPositionAbstract
65	NON-CURRENT ASSETS [abstract]	Abstract			ifrs-full:NoncurrentAssetsAbstract
66	Property, plant and equipment	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
67	Intangible assets	Concept (Monetary)	As Of	Debit	ifrs-full:IntangibleAssetsAndGoodwill
68	Investments in associates	Concept (Monetary)	As Of	Debit	ifrs-full:InvestmentsInAssociates
69	Investment in a joint venture	Concept (Monetary)	As Of	Debit	ifrs-full:InvestmentsInJointVentures
70	Equity investments	Concept (Monetary)	As Of	Debit	ceo:NoncurrentInvestmentsInEquityInstruments
71	Deferred tax assets	Concept (Monetary)	As Of	Debit	ifrs-full:NetDeferredTaxAssets
72	Other non-current assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherNoncurrentAssets
73	Total non-current assets	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentAssets
74	CURRENT ASSETS [abstract]	Abstract			ifrs-full:CurrentAssetsAbstract
75	Inventories and supplies	Concept (Monetary)	As Of	Debit	ifrs-full:Inventories
76	Trade receivables	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentTradeReceivables
77	Due from related companies	Concept (Monetary)	As Of	Debit	ifrs-full:TradeAndOtherCurrentReceivablesDueFromRelatedParties
78	Equity investments	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentInvestmentsInEquityInstrumentsDesignatedAtFairValueThroughOtherComprehensiveIncome
79	Other financial assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherCurrentFinancialAssets
80	Other current assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherCurrentAssets
81	Time deposits with maturity over three months	Concept (Monetary)	As Of	Debit	ifrs-full:ShorttermDepositsNotClassifiedAsCashEquivalents
82	Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
83	Total current assets	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentAssets
84	CURRENT LIABILITIES [abstract]	Abstract			ifrs-full:CurrentLiabilitiesAbstract
85	Loans and borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentBorrowingsAndCurrentPortionOfNoncurrentBorrowings
86	Borrowings from the parent company	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
87	Trade and accrued payables	Concept (Monetary)	As Of	Credit	ifrs-full:TradeAndOtherCurrentPayablesToTradeSuppliers
88	Due to the parent company	Concept (Monetary)	As Of	Credit	ceo:OtherPayablesAndAccruedLiabilitiesDueToParentCompany
89	Due to related companies	Concept (Monetary)	As Of	Credit	ceo:TradeAndAccruedPayablesDueToOtherRelatedParties
90	Contract liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentContractLiabilities
91	Other payables and accrued liabilities	Concept (Monetary)	As Of	Credit	ceo:OtherPayablesAndAccruedLiabilitiesExcludingPayablesDueToParentCompany
92	Taxes payable	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentTaxLiabilitiesCurrent
93	Total current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentLiabilities
94	NET CURRENT ASSETS	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentAssetsLiabilities
95	TOTAL ASSETS LESS CURRENT LIABILITIES	Concept (Monetary)	As Of	Debit	ifrs-full:AssetsLessCurrentLiabilities
96	NON-CURRENT LIABILITIES [abstract]	Abstract			ifrs-full:NoncurrentLiabilitiesAbstract
97	Loans and borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:LongtermBorrowings
98	Provision for dismantlement	Concept (Monetary)	As Of	Credit	ifrs-full:ProvisionForDecommissioningRestorationAndRehabilitationCosts
99	Deferred tax liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NetDeferredTaxLiabilities
100	Other non-current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:OtherNoncurrentLiabilities
101	Total non-current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentLiabilities
102	NET ASSETS	Concept (Monetary)	As Of	Debit	ifrs-full:NetAssetsLiabilities
103	EQUITY [abstract]	Abstract			ifrs-full:EquityAbstract
104	Equity attributable to owners of the parent	Abstract			ceo:EquityAttributableToOwnersOfParentAbstract
105	Issued capital	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
106	Reserves	Concept (Monetary)	As Of	Credit	ceo:Reserves
107	TOTAL EQUITY	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
108	00300 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY	Network	*	*	http://www.cnoocltd.com/role/ConsolidatedStatementsOfChangesInEquity
109	Statement of changes in equity [table]	Table	*	*	ifrs-full:StatementOfChangesInEquityTable
110	Components of equity [axis]	Axis			ifrs-full:ComponentsOfEquityAxis
111	Equity [member]	Member			ifrs-full:EquityMember
112	Issued capital [member]	Member			ifrs-full:IssuedCapitalMember
113	Cumulative translation reserve [member]	Member			ifrs-full:ReserveOfExchangeDifferencesOnTranslationMember
114	Statutory and non-distributable reserves [member]	Member			ceo:StatutoryAndNondistributableReservesMember
115	Other reserves [member]	Member			ifrs-full:OtherReservesMember
116	Retained earnings [member]	Member			ifrs-full:RetainedEarningsMember
117	Proposed final dividend [member]	Member			ceo:ProposedFinalDividendMember
118	Total [member]	Member			ifrs-full:EquityAttributableToOwnersOfParentMember
119	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
120	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
121	CNOOC China Limited [member]	Member			ceo:CnoocChinaLimitedMember
122	Retrospective application and retrospective restatement [axis]	Axis			ifrs-full:RetrospectiveApplicationAndRetrospectiveRestatementAxis
123	Currently stated [member]	Member			ifrs-full:RestatedMember
124	Increase (decrease) due to application of IFRS 15 [member]	Member			ifrs-full:IncreaseDecreaseDueToApplicationOfIFRS15Member
125	Statement of changes in equity [line items]	LineItems			ifrs-full:StatementOfChangesInEquityLineItems
126	Balance at beginning of year	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
127	Impact of adopting IFRS 15/HKFRS 15	Concept (Monetary)	For Period	Debit	ceo:CumulativeEffectOnRetainedEarningsDueToImpactOfAdoptingNewAccountingPolicies
128	Profit for the year	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossAttributableToOwnersOfParent
129	Other comprehensive income/(expense), net of income tax	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncome
130	Total comprehensive income/(expense)	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncome
131	Final dividend	Concept (Monetary)	For Period	Debit	ifrs-full:DividendsRecognisedAsDistributionsToOwnersOfParentRelatingToPriorYears
132	Interim dividend	Concept (Monetary)	For Period	Debit	ifrs-full:DividendsRecognisedAsDistributionsToOwnersOfParentRelatingToCurrentYear
133	Proposed final dividend	Concept (Monetary)	For Period		ifrs-full:DividendsProposedOrDeclaredBeforeFinancialStatementsAuthorisedForIssueButNotRecognisedAsDistributionToOwners
134	Appropriation to reserve	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughAppropriationOfRetainedEarnings
135	Disposal of investments in equity instruments at FVTOCI	Concept (Monetary)	For Period	Credit	ifrs-full:CumulativeGainLossOnDisposalOfInvestmentsInEquityInstrumentsDesignatedAsMeasuredAtFairValueThroughOtherComprehensiveIncome
136	Balance at end of year	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
137	Reserves	Concept (Monetary)	As Of	Credit	ceo:Reserves
138	00400 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS	Network	*	*	http://www.cnoocltd.com/role/ConsolidatedStatementsOfCashFlows
139	Implied Table	Table	*	*	implied:Table
140	CONSOLIDATED STATEMENTS OF CASH FLOWS [abstract]	Abstract			ifrs-full:StatementOfCashFlowsAbstract
141	CASH FLOWS FROM OPERATING ACTIVITIES [abstract]	Abstract			ifrs-full:CashFlowsFromUsedInOperatingActivitiesAbstract
142	Cash generated from operations	Concept (Monetary)	For Period		ifrs-full:CashFlowsFromUsedInOperations
143	Income taxes paid	Concept (Monetary)	For Period	Credit	ifrs-full:IncomeTaxesPaidRefundClassifiedAsOperatingActivities
144	Net cash flows from operating activities	Concept (Monetary)	For Period		ifrs-full:CashFlowsFromUsedInOperatingActivities
145	CASH FLOWS FROM INVESTING ACTIVITIES [abstract]	Abstract			ifrs-full:CashFlowsFromUsedInInvestingActivitiesAbstract
146	Acquisition of oil and gas properties	Concept (Monetary)	For Period	Credit	ifrs-full:PurchaseOfOilAndGasAssets
147	Capital expenditure	Concept (Monetary)	For Period	Credit	ifrs-full:PurchaseOfPropertyPlantAndEquipmentIntangibleAssetsOtherThanGoodwillInvestmentPropertyAndOtherNoncurrentAssets
148	Additions to investments in associates	Concept (Monetary)	For Period	Credit	ifrs-full:PurchaseOfInterestsInAssociates
149	Decrease in time deposits with maturity over three months	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromUsedInDecreaseIncreaseInShorttermDepositsAndInvestments
150	Dividends received from associates	Concept (Monetary)	For Period	Debit	ifrs-full:DividendsReceivedFromAssociatesClassifiedAsInvestingActivities
151	Dividends received from a joint venture	Concept (Monetary)	For Period	Debit	ifrs-full:DividendsReceivedFromJointVenturesClassifiedAsInvestingActivities
152	Interest received	Concept (Monetary)	For Period	Debit	ifrs-full:InterestReceivedClassifiedAsInvestingActivities
153	Investment income received	Concept (Monetary)	For Period	Debit	ceo:InvestmentIncomeReceivedClassifiedAsInvestingActivities
154	Purchase of other financial assets	Concept (Monetary)	For Period	Credit	ceo:PurchaseOfOtherFinancialAssets
155	Purchase of equity investments	Concept (Monetary)	For Period	Credit	ceo:PurchaseOfEquityInvestments
156	Proceeds from sale of other financial assets	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromSalesOrMaturityOfFinancialInstrumentsClassifiedAsInvestingActivities
157	Proceeds from sale of equity investments	Concept (Monetary)	For Period	Debit	ceo:ProceedsFromSalesOfEquityInvestmentsClassifiedAsInvestingActivities
158	Proceeds from disposal of property, plant and equipment	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromDisposalsOfPropertyPlantAndEquipmentIntangibleAssetsOtherThanGoodwillInvestmentPropertyAndOtherNoncurrentAssets
159	Proceeds from disposal of an associate	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromSalesOfInterestsInAssociates
160	Net cash flows used in investing activities	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromUsedInInvestingActivities
161	CASH FLOWS FROM FINANCING ACTIVITIES [abtract]	Abstract			ifrs-full:CashFlowsFromUsedInFinancingActivitiesAbstract
162	Proceeds from issuance of guaranteed notes	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromIssueOfBondsNotesAndDebentures
163	Repayment of guaranteed notes	Concept (Monetary)	For Period	Credit	ifrs-full:RepaymentsOfBondsNotesAndDebentures
164	Proceeds from bank loans	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromBorrowingsClassifiedAsFinancingActivities
165	Repayment of bank loans	Concept (Monetary)	For Period	Credit	ifrs-full:RepaymentsOfBorrowingsClassifiedAsFinancingActivities
166	Dividends paid	Concept (Monetary)	For Period	Credit	ifrs-full:DividendsPaidClassifiedAsFinancingActivities
167	Interest paid	Concept (Monetary)	For Period	Credit	ifrs-full:InterestPaidClassifiedAsFinancingActivities
168	Net cash flows used in financing activities	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromUsedInFinancingActivities
169	NET INCREASE/(DECREASE) IN CASH AND CASH EQUIVALENTS	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseInCashAndCashEquivalentsBeforeEffectOfExchangeRateChanges
170	Cash and cash equivalents at beginning of year	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
171	Effect of foreign exchange rate changes, net	Concept (Monetary)	For Period	Debit	ifrs-full:EffectOfExchangeRateChangesOnCashAndCashEquivalents
172	CASH AND CASH EQUIVALENTS AT END OF YEAR	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
173	10101 - Disclosure - CORPORATE INFORMATION	Network	*	*	http://www.cnoocltd.com/role/CorporateInformation
174	Implied Table	Table	*	*	implied:Table
175	CORPORATE INFORMATION [abstract]	Abstract			ceo:CorporateInformationAbstract
176	Disclosure of corporate information	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfCorporateInformationExplanatory
177	10201 - Disclosure - STATEMENT OF COMPLIANCE	Network	*	*	http://www.cnoocltd.com/role/StatementOfCompliance
178	Implied Table	Table	*	*	implied:Table
179	STATEMENT OF COMPLIANCE [abstract]	Abstract			ceo:StatementOfComplianceAbstract
180	Disclosure of statement of compliance	Concept (Text Block (HTML))	For Period		ifrs-full:StatementOfIFRSCompliance
181	10202 - Disclosure - CHANGES IN ACCOUNTING POLICIES AND DISCLOSURES	Network	*	*	http://www.cnoocltd.com/role/ChangesInAccountingPoliciesAndDisclosures
182	Implied Table	Table	*	*	implied:Table
183	CHANGES IN ACCOUNTING POLICIES AND DISCLOSURES [abstract]	Abstract			ceo:ChangesInAccountingPoliciesAndDisclosuresAbstract
184	Disclosure of changes in accounting policies and disclosures	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfChangesInAccountingPolicyAndDisclosuresExplanatory
185	10301 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	Network	*	*	http://www.cnoocltd.com/role/SummaryOfSignificantAccountingPolicies
186	Implied Table	Table	*	*	implied:Table
187	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES [abstract]	Abstract			ceo:SummaryOfSignificantAccountingPoliciesAbstract
188	Disclosure of summary of significant accounting policies	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfSummaryOfSignificantAccountingPoliciesExplanatory
189	10401 - Disclosure - OIL AND GAS SALES AND MARKETING REVENUES	Network	*	*	http://www.cnoocltd.com/role/OilAndGasSalesAndMarketingRevenues
190	Implied Table	Table	*	*	implied:Table
191	OIL AND GAS SALES AND MARKETING REVENUES [abstract]	Abstract			ceo:OilAndGasSalesAndMarketingRevenuesAbstract
192	Disclosure of oil and gas sales and marketing revenues	Concept (Text Block (HTML))	For Period		ceo:OilAndGasSalesAndMarketingRevenuesExplanatory
193	10501 - Disclosure - SEGMENT INFORMATION	Network	*	*	http://www.cnoocltd.com/role/SegmentInformation
194	Implied Table	Table	*	*	implied:Table
195	SEGMENT INFORMATION [abstract]	Abstract			ifrs-full:DisclosureOfOperatingSegmentsAbstract
196	Disclosure of segment information	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfOperatingSegmentsExplanatory
197	10601 - Disclosure - PROFIT BEFORE TAX	Network	*	*	http://www.cnoocltd.com/role/ProfitBeforeTax
198	Implied Table	Table	*	*	implied:Table
199	PROFIT BEFORE TAX [abstract]	Abstract			ceo:ProfitBeforeTaxAbstract
200	Disclosure of profit before tax	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfProfitLossBeforeTaxExplanatory
201	10701 - Disclosure - FINANCE COSTS	Network	*	*	http://www.cnoocltd.com/role/FinanceCosts
202	Implied Table	Table	*	*	implied:Table
203	FINANCE COSTS [abstract]	Abstract			ifrs-full:BorrowingCostsAbstract
204	Disclosure of finance costs	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinanceCostExplanatory
205	10801 - Disclosure - KEY MANAGEMENT PERSONNEL'S REMUNERATION	Network	*	*	http://www.cnoocltd.com/role/KeyManagementPersonnelsRemuneration
206	Implied Table	Table	*	*	implied:Table
207	KEY MANAGEMENT PERSONNEL'S REMUNERATION [abstract]	Abstract			ceo:KeyManagementPersonnelsRemunerationAbstract
208	Disclosure of key management personnel's remuneration	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInformationAboutKeyManagementPersonnelExplanatory
209	10901 - Disclosure - FIVE HIGHEST PAID EMPLOYEES	Network	*	*	http://www.cnoocltd.com/role/FiveHighestPaidEmployees
210	Implied Table	Table	*	*	implied:Table
211	FIVE HIGHEST PAID EMPLOYEES [abstract]	Abstract			ceo:FiveHighestPaidEmployeesAbstract
212	Disclosure of five highest paid employees	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInformationAboutEmployeesExplanatory
213	11001 - Disclosure - TAX	Network	*	*	http://www.cnoocltd.com/role/Tax
214	Implied Table	Table	*	*	implied:Table
215	TAX [abstract]	Abstract			ifrs-full:MajorComponentsOfTaxExpenseIncomeAbstract
216	Disclosure of tax	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfTaxReceivablesAndPayablesExplanatory
217	11101 - Disclosure - EARNINGS PER SHARE	Network	*	*	http://www.cnoocltd.com/role/EarningsPerShare
218	Implied Table	Table	*	*	implied:Table
219	EARNINGS PER SHARE [abstract]	Abstract			ifrs-full:EarningsPerShareAbstract
220	Disclosure of earnings per share	Concept (Text Block (HTML))	For Period		ifrs-full:EarningsPerShareExplanatory
221	11201 - Disclosure - DIVIDENDS	Network	*	*	http://www.cnoocltd.com/role/Dividends
222	Implied Table	Table	*	*	implied:Table
223	DIVIDENDS [abstract]	Abstract			ceo:DividendsAbstract
224	Disclosure of dividends	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDividendsExplanatory
225	11301 - Disclosure - PROPERTY, PLANT AND EQUIPMENT	Network	*	*	http://www.cnoocltd.com/role/PropertyPlantAndEquipment
226	Implied Table	Table	*	*	implied:Table
227	PROPERTY, PLANT AND EQUIPMENT [abstract]	Abstract			ifrs-full:PropertyPlantAndEquipmentAbstract
228	Disclosure of property, plant and equipment	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfPropertyPlantAndEquipmentExplanatory
229	11401 - Disclosure - INTANGIBLE ASSETS	Network	*	*	http://www.cnoocltd.com/role/IntangibleAssets
230	Implied Table	Table	*	*	implied:Table
231	INTANGIBLE ASSETS [abstract]	Abstract			ifrs-full:IntangibleAssetsAndGoodwillAbstract
232	Disclosure of intangible assets	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfIntangibleAssetsExplanatory
233	11501 - Disclosure - INVESTMENTS IN ASSOCIATES	Network	*	*	http://www.cnoocltd.com/role/InvestmentsInAssociates
234	Implied Table	Table	*	*	implied:Table
235	INVESTMENTS IN ASSOCIATES [abstract]	Abstract			ifrs-full:DisclosureOfSignificantInvestmentsInAssociatesAbstract
236	Disclosure of investments in associates	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInterestsInAssociatesExplanatory
237	11601 - Disclosure - INVESTMENT IN A JOINT VENTURE	Network	*	*	http://www.cnoocltd.com/role/InvestmentInAJointVenture
238	Implied Table	Table	*	*	implied:Table
239	INVESTMENT IN A JOINT VENTURE [abstract]	Abstract			ifrs-full:DisclosureOfJointVenturesAbstract
240	Disclosure of investment in a joint venture	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfJointVenturesExplanatory
241	11701 - Disclosure - EQUITY INVESTMENTS AND OTHER FINANCIAL ASSETS	Network	*	*	http://www.cnoocltd.com/role/EquityInvestmentsAndOtherFinancialAssets
242	Implied Table	Table	*	*	implied:Table
243	EQUITY INVESTMENTS AND OTHER FINANCIAL ASSETS [abstract]	Abstract			ifrs-full:DisclosureOfFinancialAssetsAbstract
244	Disclosure of equity investments and other financial assets	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinancialAssetsExplanatory
245	11801 - Disclosure - OTHER NON-CURRENT ASSETS	Network	*	*	http://www.cnoocltd.com/role/OtherNoncurrentAssets
246	Implied Table	Table	*	*	implied:Table
247	OTHER NON-CURRENT ASSETS [abstract]	Abstract			ifrs-full:MiscellaneousNoncurrentAssetsAbstract
248	Disclosure of other non-current assets	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfOtherNoncurrentAssetsExplanatory
249	11901 - Disclosure - INVENTORIES AND SUPPLIES	Network	*	*	http://www.cnoocltd.com/role/InventoriesAndSupplies
250	Implied Table	Table	*	*	implied:Table
251	INVENTORIES AND SUPPLIES [abstract]	Abstract			ifrs-full:ClassesOfInventoriesAbstract
252	Disclosure of inventories and supplies	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInventoriesExplanatory
253	12001 - Disclosure - TRADE RECEIVABLES	Network	*	*	http://www.cnoocltd.com/role/TradeReceivables
254	Implied Table	Table	*	*	implied:Table
255	TRADE RECEIVABLES [abstract]	Abstract			ifrs-full:TradeAndOtherReceivablesAbstract
256	Disclosure of trade receivables	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfTradeAndOtherReceivablesExplanatory
257	12101 - Disclosure - CASH AND CASH EQUIVALENTS AND TIME DEPOSITS WITH MATURITY OVER THREE MONTHS	Network	*	*	http://www.cnoocltd.com/role/CashAndCashEquivalentsAndTimeDepositsWithMaturityOverThreeMonths
258	Implied Table	Table	*	*	implied:Table
259	CASH AND CASH EQUIVALENTS AND TIME DEPOSITS WITH MATURITY OVER THREE MONTHS [abstract]	Abstract			ceo:CashAndCashEquivalentsAndTimeDepositsWithMaturityOverThreeMonthsAbstract
260	Disclosure of cash and cash equivalents and time deposits with maturity over three months	Concept (Text Block (HTML))	For Period		ceo:CashAndCashEquivalentsAndTimeDepositsWithMaturityOverThreeMonthsExplanatory
261	12201 - Disclosure - TRADE AND ACCRUED PAYABLES	Network	*	*	http://www.cnoocltd.com/role/TradeAndAccruedPayables
262	Implied Table	Table	*	*	implied:Table
263	TRADE AND ACCRUED PAYABLES [abstract]	Abstract			ifrs-full:TradeAndOtherPayablesAbstract
264	Disclosure of trade and accrued payables	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfTradeAndOtherPayablesExplanatory
265	12301 - Disclosure - CONTRACT LIABILITIES	Network	*	*	http://www.cnoocltd.com/role/ContractLiabilities
266	Implied Table	Table	*	*	implied:Table
267	CONTRACT LIABILITIES [abstract]	Abstract			ifrs-full:ContractLiabilitiesAbstract
268	Disclosure of contract liabilities	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfContractLiabilitiesExplanatory
269	12401 - Disclosure - OTHER PAYABLES AND ACCRUED LIABILITIES	Network	*	*	http://www.cnoocltd.com/role/OtherPayablesAndAccruedLiabilities
270	Implied Table	Table	*	*	implied:Table
271	OTHER PAYABLES AND ACCRUED LIABILITIES [abstract]	Abstract			ceo:OtherPayablesAndAccruedLiabilitiesAbstract
272	Disclosure of other payables and accrued liabilities	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfOtherPayablesAndAccruedLiabilitiesExplanatory
273	12501 - Disclosure - LOANS AND BORROWINGS	Network	*	*	http://www.cnoocltd.com/role/LoansAndBorrowings
274	Implied Table	Table	*	*	implied:Table
275	LOANS AND BORROWINGS [abstract]	Abstract			ifrs-full:BorrowingsAbstract
276	Disclosure of loans and borrowings	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfBorrowingsExplanatory
277	12601 - Disclosure - PROVISION FOR DISMANTLEMENT	Network	*	*	http://www.cnoocltd.com/role/ProvisionForDismantlement
278	Implied Table	Table	*	*	implied:Table
279	PROVISION FOR DISMANTLEMENT [abstract]	Abstract			ifrs-full:ProvisionForDecommissioningRestorationAndRehabilitationCostsAbstract
280	Disclosure of provision for dismantlement	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfProvisionForDismantlementExplanatory
281	12701 - Disclosure - SHARE CAPITAL	Network	*	*	http://www.cnoocltd.com/role/ShareCapital
282	Implied Table	Table	*	*	implied:Table
283	SHARE CAPITAL [abstract]	Abstract			ifrs-full:DisclosureOfClassesOfShareCapitalAbstract
284	Disclosure of share capital	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfClassesOfShareCapitalExplanatory
285	12801 - Disclosure - RESERVES	Network	*	*	http://www.cnoocltd.com/role/Reserves
286	Implied Table	Table	*	*	implied:Table
287	RESERVES [abstract]	Abstract			ifrs-full:DisclosureOfReservesWithinEquityAbstract
288	Disclosure of reserves	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfReservesAndOtherEquityInterestExplanatory
289	12901 - Disclosure - RELATED PARTY TRANSACTIONS	Network	*	*	http://www.cnoocltd.com/role/RelatedPartyTransactions
290	Implied Table	Table	*	*	implied:Table
291	RELATED PARTY TRANSACTIONS [abstract]	Abstract			ifrs-full:RelatedPartyTransactionsAbstract
292	Disclosure of related party transactions	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfRelatedPartyExplanatory
293	13001 - Disclosure - RETIREMENT BENEFITS	Network	*	*	http://www.cnoocltd.com/role/RetirementBenefits
294	Implied Table	Table	*	*	implied:Table
295	RETIREMENT BENEFITS [abstract]	Abstract			ceo:DisclosureOfRetirementBenefitsAbstract
296	Disclosure of retirement benefits	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfRetirementBenefitsExplanatory
297	13101 - Disclosure - NOTE TO THE CONSOLIDATED STATEMENT OF CASH FLOWS	Network	*	*	http://www.cnoocltd.com/role/NoteToTheConsolidatedStatementOfCashFlows
298	Implied Table	Table	*	*	implied:Table
299	NOTE TO THE CONSOLIDATED STATEMENT OF CASH FLOWS [abstract]	Abstract			ceo:NoteToConsolidatedStatementOfCashFlowsAbstract
300	Disclosure of note to the consolidated statement of cash flows	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfCashFlowStatementExplanatory
301	13201 - Disclosure - COMMITMENTS AND CONTINGENCIES	Network	*	*	http://www.cnoocltd.com/role/CommitmentsAndContingencies
302	Implied Table	Table	*	*	implied:Table
303	COMMITEMENTS AND CONTINGENCIES [abstract]	Abstract			ceo:DisclosureOfCommitmentsAndContingenciesAbstract
304	Disclosure of commitments and contingencies	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfCommitmentsAndContingentLiabilitiesExplanatory
305	13301 - Disclosure - FINANCIAL INSTRUMENTS	Network	*	*	http://www.cnoocltd.com/role/FinancialInstruments
306	Implied Table	Table	*	*	implied:Table
307	FINANCIAL INSTRUMENTS [abstract]	Abstract			ifrs-full:DisclosureOfFinancialInstrumentsAbstract
308	Disclosure of financial instruments	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinancialInstrumentsExplanatory
309	13401 - Disclosure - CONCENTRATION OF CUSTOMERS	Network	*	*	http://www.cnoocltd.com/role/ConcentrationOfCustomers
310	Implied Table	Table	*	*	implied:Table
311	CONCENTRATION OF CUSTOMERS [abstract]	Abstract			ifrs-full:DisclosureOfMajorCustomersAbstract
312	Disclosure of concentration of customers	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfSegmentsMajorCustomersExplanatory
313	13501 - Disclosure - FINANCIAL RISK MANAGEMENT OBJECTIVES AND POLICIES	Network	*	*	http://www.cnoocltd.com/role/FinancialRiskManagementObjectivesAndPolicies
314	Implied Table	Table	*	*	implied:Table
315	FINANCIAL RISK MANAGEMENT OBJECTIVES AND POLICIES [abstract]	Abstract			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsAbstract
316	Disclosure of financial risk management objectives and policies	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsExplanatory
317	13601 - Disclosure - CHARGES OF ASSETS	Network	*	*	http://www.cnoocltd.com/role/ChargesOfAssets
318	Implied Table	Table	*	*	implied:Table
319	CHARGES OF ASSETS [abstract]	Abstract			ceo:ChargesOfAssetsAbstract
320	Disclosure of charges of assets	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfChargesOfAssetsExplanatory
321	13701 - Disclosure - SUBSEQUENT EVENTS	Network	*	*	http://www.cnoocltd.com/role/SubsequentEvents
322	Implied Table	Table	*	*	implied:Table
323	SUBSEQUENT EVENTS [abstract]	Abstract			ceo:SubsequentEventsAbstract
324	Disclosure of subsequent events	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfEventsAfterReportingPeriodExplanatory
325	13801 - Disclosure - APPROVAL OF THE FINANCIAL STATEMENTS	Network	*	*	http://www.cnoocltd.com/role/ApprovalOfTheFinancialStatements
326	Implied Table	Table	*	*	implied:Table
327	APPROVAL OF THE FINANCIAL STATEMENTS [abstract]	Abstract			ceo:ApprovalOfFinancialStatementsAbstract
328	Disclosure of approval of the financial statements	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfApprovalOfFinancialStatementsExplanatory
329	20302 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	Network	*	*	http://www.cnoocltd.com/role/SummaryOfSignificantAccountingPoliciesPolicies
330	Implied Table	Table	*	*	implied:Table
331	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES [abstract]	Abstract			ceo:SummaryOfSignificantAccountingPoliciesAbstract
332	Basis of preparation	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfBasisOfPreparationOfFinancialStatementsExplanatory
333	Basis of consolidation	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForBusinessCombinationsExplanatory
334	Business combinations and goodwill	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForBusinessCombinationsAndGoodwillExplanatory
335	Subsidiaries	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForSubsidiariesExplanatory
336	Associates	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForInvestmentInAssociates
337	Joint arrangements	Concept (Text Block (HTML))	For Period		ceo:DescriptionOfAccountingPolicyForJointArrangementsExplanatory
338	Related parties	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForTransactionsWithRelatedPartiesExplanatory
339	Impairment of non-financial assets other than goodwill	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForImpairmentOfNonfinancialAssetsExplanatory
340	Property, plant and equipment	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForPropertyPlantAndEquipmentExplanatory
341	Intangible assets other than goodwill	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForIntangibleAssetsOtherThanGoodwillExplanatory
342	Major maintenance and repairs	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForRepairsAndMaintenanceExplanatory
343	Research and development costs	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForResearchAndDevelopmentExpenseExplanatory
344	Financial assets	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForFinancialAssetsExplanatory
345	Fair value	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForFairValueMeasurementExplanatory
346	Impairment of financial assets	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForImpairmentOfFinancialAssetsExplanatory
347	Derecognition of financial assets	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForDerecognitionOfFinancialInstrumentsExplanatory
348	Financial liabilities at amortized cost (including interest-bearing loans and borrowings)	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForFinancialLiabilitiesExplanatory
349	Derecognition of financial liabilities	Concept (Text Block (HTML))	For Period		ceo:DescriptionOfAccountingPolicyForDerecognitionOfFinancialLiabilitiesExplanatory
350	Offsetting of financial instruments	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForOffsettingOfFinancialInstrumentsExplanatory
351	Inventories and supplies	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForMeasuringInventories
352	Cash and cash equivalents	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyToDetermineComponentsOfCashAndCashEquivalents
353	Provisions	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForProvisionsExplanatory
354	Income tax	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForIncomeTaxExplanatory
355	Revenue	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForRecognitionOfRevenue
356	Share-based payment transactions	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForSharebasedPaymentTransactionsExplanatory
357	Retirement and termination benefits	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForEmployeeBenefitsExplanatory
358	Borrowing costs	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForBorrowingCostsExplanatory
359	Foreign currencies	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForForeignCurrencyTranslationExplanatory
360	Operating leases	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForLeasesExplanatory
361	Contingencies	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForContingentLiabilitiesAndContingentAssetsExplanatory
362	Significant accounting judgements, estimates and assumptions	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfAccountingJudgementsAndEstimatesExplanatory
363	30103 - Disclosure - CORPORATE INFORMATION (Tables)	Network	*	*	http://www.cnoocltd.com/role/CorporateInformationTables
364	Implied Table	Table	*	*	implied:Table
365	CORPORATE INFORMATION [abstract]	Abstract			ceo:CorporateInformationAbstract
366	Schedule of particulars of the principal subsidiaries at the end of the reporting period	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesExplanatory
367	30203 - Disclosure - CHANGES IN ACCOUNTING POLICIES AND DISCLOSURES (Tables)	Network	*	*	http://www.cnoocltd.com/role/ChangesInAccountingPoliciesAndDisclosuresTables
368	Implied Table	Table	*	*	implied:Table
369	CHANGES IN ACCOUNTING POLICIES AND DISCLOSURES [abstract]	Abstract			ceo:ChangesInAccountingPoliciesAndDisclosuresAbstract
370	Schedule of impact of transition to IFRS 15/HKFRS 15 on retained earnings	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfImpactOfTransitionToIfrs15AndHkfrs15OnRetainedEarningsTableExplanatory
371	Schedule of adjustments to the amounts recognized in the consolidated statement of financial position	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfAdjustmentsToConsolidatedStatementOfFinancialPositionDueToApplicationOfIFRS15AndHKFRS15TableExplanatory
372	Schedule of impacts of applying IFRS 15/HKFRS 15 on the Group's consolidated statement of profit or loss and other comprehensive income	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfImpactOnConsolidatedStatementOfProfitOrLossAndOtherComprehensiveIncomeDueToApplicationOfIFRS15AndHKFRS15TableExplanatory
373	Schedule of impacts of applying IFRS 15/HKFRS 15 on the Group's consolidated statement of financial position	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfImpactOnConsolidatedStatementOfFinancialPositionDueToApplicationOfIFRS15AndHKFRS15TableExplanatory
374	Schedule of impacts of applying IFRS 15/HKFRS 15 on the Group's consolidated statement of cash flows	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfImpactOnConsolidatedStatementOfCashFlowsDueToApplicationOfIFRS15AndHKFRS15TableExplanatory
375	30403 - Disclosure - OIL AND GAS SALES AND MARKETING REVENUES (Tables)	Network	*	*	http://www.cnoocltd.com/role/OilAndGasSalesAndMarketingRevenuesTables
376	Implied Table	Table	*	*	implied:Table
377	OIL AND GAS SALES AND MARKETING REVENUES [abstract]	Abstract			ceo:OilAndGasSalesAndMarketingRevenuesAbstract
378	Schedule of oil and gas sales and marketing revenues	Concept (Text Block (HTML))	For Period		ceo:OilAndGasSalesAndMarketingRevenuesTableExplanatory
379	30503 - Disclosure - SEGMENT INFORMATION (Tables)	Network	*	*	http://www.cnoocltd.com/role/SegmentInformationTable
380	Implied Table	Table	*	*	implied:Table
381	SEGMENT INFORMATION [abstract]	Abstract			ifrs-full:DisclosureOfOperatingSegmentsAbstract
382	Schedule of segment financial information	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfSegmentFinancialInformationTableExplanatory
383	Schedule of certain non-current assets information for the Group's geographical information	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfGeographicalAreasExplanatory
384	30603 - Disclosure - PROFIT BEFORE TAX (Tables)	Network	*	*	http://www.cnoocltd.com/role/ProfitBeforeTaxTables
385	Implied Table	Table	*	*	implied:Table
386	PROFIT BEFORE TAX [abstract]	Abstract			ceo:ProfitBeforeTaxAbstract
387	Schedule of profit before tax	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfProfitLossBeforeTaxTableExplanatory
388	30703 - Disclosure - FINANCE COSTS (Tables)	Network	*	*	http://www.cnoocltd.com/role/FinanceCostsTables
389	Implied Table	Table	*	*	implied:Table
390	FINANCE COSTS [abstract]	Abstract			ifrs-full:BorrowingCostsAbstract
391	Schedule of finance costs	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfBorrowingCostsExplanatory
392	30803 - Disclosure - KEY MANAGEMENT PERSONNEL'S REMUNERATION (Tables)	Network	*	*	http://www.cnoocltd.com/role/KeyManagementPersonnelsRemunerationTables
393	Implied Table	Table	*	*	implied:Table
394	KEY MANAGEMENT PERSONNEL'S REMUNERATION [abstract]	Abstract			ceo:KeyManagementPersonnelsRemunerationAbstract
395	Schedule of directors' remuneration	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfDirectorsRemunerationTableExplanatory
396	Schedule of other key management personnel's (excluding Directors') remuneration	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfOtherKeyManagementPersonnelsExcludingDirectorsRemunerationTableExplanatory
397	30903 - Disclosure - FIVE HIGHEST PAID EMPLOYEES (Tables)	Network	*	*	http://www.cnoocltd.com/role/FiveHighestPaidEmployeesTables
398	Implied Table	Table	*	*	implied:Table
399	FIVE HIGHEST PAID EMPLOYEES [abstract]	Abstract			ceo:FiveHighestPaidEmployeesAbstract
400	Schedule of remuneration of five highest paid emloyees	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfDetailedInformationAboutRemunerationOfFiveHighestPaidEmployeesTableExplanatory
401	Schedule of remuneration bands of five highest paid employees	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfRemunerationBandsOfFiveHighestPaidEmployeesTableExplanatory
402	31003 - Disclosure - TAX (Tables)	Network	*	*	http://www.cnoocltd.com/role/TaxTables
403	Implied Table	Table	*	*	implied:Table
404	TAX [abstract]	Abstract			ifrs-full:MajorComponentsOfTaxExpenseIncomeAbstract
405	Schedule of analysis of tax (credit)/expense in consolidated statement of profit or loss and other comprehensive income	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfIncomeTaxExplanatory
406	Schedule of reconciliation of the PRC statutory corporate income tax rate to effective income tax rate of the Group	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfReconciliationOfStatutoryCorporateIncomeTaxRateToEffectiveIncomeTaxRateOfGroupTableExplanatory
407	Schedule of movements of deferred tax liabilities net of deferred tax assets	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDeferredTaxesExplanatory
408	Schedule of principal components of deferred tax balances	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsExplanatory
409	31103 - Disclosure - EARNINGS PER SHARE (Tables)	Network	*	*	http://www.cnoocltd.com/role/EarningsPerShareTables
410	Implied Table	Table	*	*	implied:Table
411	EARNINGS PER SHARE [abstract]	Abstract			ifrs-full:EarningsPerShareAbstract
412	Schedule of earnings per share	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfEarningsPerShareTableExplanatory
413	31203 - Disclosure - DIVIDENDS (Tables)	Network	*	*	http://www.cnoocltd.com/role/DividendsTables
414	Implied Table	Table	*	*	implied:Table
415	DIVIDENDS [abstract]	Abstract			ceo:DividendsAbstract
416	Schedule of dividends	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfDividendsTableExplanatory
417	31303 - Disclosure - PROPERTY, PLANT AND EQUIPMENT (Tables)	Network	*	*	http://www.cnoocltd.com/role/PropertyPlantAndEquipmentTables
418	Implied Table	Table	*	*	implied:Table
419	PROPERTY, PLANT AND EQUIPMENT [abstract]	Abstract			ifrs-full:PropertyPlantAndEquipmentAbstract
420	Schedule of property, plant and equipment	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDetailedInformationAboutPropertyPlantAndEquipmentExplanatory
421	31403 - Disclosure - INTANGIBLE ASSETS (Tables)	Network	*	*	http://www.cnoocltd.com/role/IntangibleAssetsTables
422	Implied Table	Table	*	*	implied:Table
423	INTANGIBLE ASSETS [abstract]	Abstract			ifrs-full:IntangibleAssetsAndGoodwillAbstract
424	Schedule of intangible assets	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfReconciliationOfChangesInIntangibleAssetsAndGoodwillExplanatory
425	31503 - Disclosure - INVESTMENTS IN ASSOCIATES (Tables)	Network	*	*	http://www.cnoocltd.com/role/InvestmentsInAssociatesTables
426	Implied Table	Table	*	*	implied:Table
427	INVESTMENTS IN ASSOCIATES [abstract]	Abstract			ifrs-full:DisclosureOfSignificantInvestmentsInAssociatesAbstract
428	Schedule of particulars of principal associates	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfParticularsOfPrincipalAssociatesTableExplanatory
429	Schedule of Group's investments in associates	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfSignificantInvestmentsInAssociatesExplanatory
430	Schedule of summarized financial information of the Group's associates in the consolidated financial statements	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfReconciliationOfSummarisedFinancialInformationOfAssociateAccountedForUsingEquityMethodToCarryingAmountOfInterestInAssociateExplanatory
431	31603 - Disclosure - INVESTMENT IN A JOINT VENTURE (Tables)	Network	*	*	http://www.cnoocltd.com/role/InvestmentInAJointVentureTables
432	Implied Table	Table	*	*	implied:Table
433	INVESTMENT IN A JOINT VENTURE [abstract]	Abstract			ifrs-full:DisclosureOfJointVenturesAbstract
434	Schedule of particulars of a joint venture	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfParticularsOfJointVenturesTableExplanatory
435	Schedule of summarized financial information of a joint venture	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfReconciliationOfSummarisedFinancialInformationOfJointVentureAccountedForUsingEquityMethodToCarryingAmountOfInterestInJointVentureExplanatory
436	31703 - Disclosure - EQUITY INVESTMENTS AND OTHER FINANCIAL ASSETS (Tables)	Network	*	*	http://www.cnoocltd.com/role/EquityInvestmentsAndOtherFinancialAssetsTables
437	Implied Table	Table	*	*	implied:Table
438	EQUITY INVESTMENTS AND OTHER FINANCIAL ASSETS [abstract]	Abstract			ifrs-full:DisclosureOfFinancialAssetsAbstract
439	Schedule of equity investments	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfEquityInvestmentsTableExplanatory
440	Schedule of other financial assets	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfOtherFinancialAssetsTableExplanatory
441	31903 - Disclosure - INVENTORIES AND SUPPLIES (Tables)	Network	*	*	http://www.cnoocltd.com/role/InventoriesAndSuppliesTables
442	Implied Table	Table	*	*	implied:Table
443	INVENTORIES AND SUPPLIES [abstract]	Abstract			ifrs-full:ClassesOfInventoriesAbstract
444	Schedule of inventories and supplies	Concept (Text Block (HTML))	For Period		ceo:InventoriesAndSuppliesTableExplanatory
445	32303 - Disclosure - CONTRACT LIABILITIES (Tables)	Network	*	*	http://www.cnoocltd.com/role/ContractLiabilitiesTables
446	Implied Table	Table	*	*	implied:Table
447	CONTRACT LIABILITIES [abstract]	Abstract			ifrs-full:ContractLiabilitiesAbstract
448	Schedule of contract liabilities	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfContractLiabilitiesTableExplanatory
449	32403 - Disclosure - OTHER PAYABLES AND ACCRUED LIABILITIES (Tables)	Network	*	*	http://www.cnoocltd.com/role/OtherPayablesAndAccruedLiabilitiesTables
450	Implied Table	Table	*	*	implied:Table
451	OTHER PAYABLES AND ACCRUED LIABILITIES [abstract]	Abstract			ceo:OtherPayablesAndAccruedLiabilitiesAbstract
452	Schedule of other payables and accrued liabilities	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfOtherPayablesAndAccruedLiabilitiesTableExplanatory
453	32503 - Disclosure - LOANS AND BORROWINGS (Tables)	Network	*	*	http://www.cnoocltd.com/role/LoansAndBorrowingsTables
454	Implied Table	Table	*	*	implied:Table
455	LOANS AND BORROWINGS [abstract]	Abstract			ifrs-full:BorrowingsAbstract
456	Schedule of current loans and borrowings	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfCurrentLoansAndBorrowingsTableExplanatory
457	Schedule of non-current loans and borrowings	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfNoncurrentLoansAndBorrowingsTableExplanatory
458	Schedule of detailed information about notes	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfDetailedInformationAboutNotesTableExplanatory
459	Schedule of maturities of long-term bank loans	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfMaturitiesOfLongtermBankLoansTebleExplanatory
460	Schedule of supplemental information with respect to the long-term bank loans	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfSupplementalInformationWithRespectToLongtermBankLoansTableExplanatory
461	32603 - Disclosure - PROVISION FOR DISMANTLEMENT (Tables)	Network	*	*	http://www.cnoocltd.com/role/ProvisionForDismantlementTables
462	Implied Table	Table	*	*	implied:Table
463	PROVISION FOR DISMANTLEMENT [abstract]	Abstract			ifrs-full:ProvisionForDecommissioningRestorationAndRehabilitationCostsAbstract
464	Schedule of provision for dismantlement	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfProvisionForDismantlementTableExplanatory
465	32703 - Disclosure - SHARE CAPITAL (Tables)	Network	*	*	http://www.cnoocltd.com/role/ShareCapitalTables
466	Implied Table	Table	*	*	implied:Table
467	SHARE CAPITAL [abstract]	Abstract			ifrs-full:DisclosureOfClassesOfShareCapitalAbstract
468	Schedule of share capital	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfShareCapitalTableExplanatory
469	Schedule of details of share options outstanding	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfNumberAndWeightedAverageExercisePricesOfShareOptionsExplanatory
470	32903 - Disclosure - RELATED PARTY TRANSACTIONS (Tables)	Network	*	*	http://www.cnoocltd.com/role/RelatedPartyTransactionsTables
471	Disclosure of transactions between related parties [table]	Table	*	*	ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesTable
472	Categories of related parties [axis]	Axis			ifrs-full:CategoriesOfRelatedPartiesAxis
473	Entity's total for related parties [member]	Member			ifrs-full:EntitysTotalForRelatedPartiesMember
474	CNOOC Group [member]	Member			ceo:ChinaNationalOffshoreOilCorporationGroupMember
475	CNOOC Finance Corporation Limited [member]	Member			ceo:CnoocFinanceCorporationLimitedMember
476	A joint venture [member]	Member			ifrs-full:JointVenturesMember
477	State-owned enterprises [member]	Member			ceo:StateownedEnterprisesMember
478	China United Coalbed Methane Corporation Limited [member]	Member			ceo:ChinaUnitedCoalbedMethaneCorporationLimitedMember
479	Disclosure of transactions between related parties [line items]	LineItems			ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesLineItems
480	Schedule of provision of exploration, oil and gas development, oil and gas production as well as marketing, management and ancillary services by the CNOOC Group to the Group	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfProvisionOfServicesByRelatedPartiesTableExplanatory
481	Schedule of sales of petroleum and natural gas products by the Group to the CNOOC Group	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfSaleOfProductsToRelatedPartiesTableExplanatory
482	Schedule of interest income received by the Group	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfInterestIncomeReceivedFromRelatedPartiesRelatedPartyTransactions
483	Schedule of deposits balances made by the Group	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfDepositsBalancesWithRelatedPartiesRelatedPartyTransactions
484	Schedule of a summary of significant related party transactions and the balances arising from related party transactions	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfSummaryOfSignificantRelatedPartyTransactionsTableExplanatory
485	33103 - Disclosure - NOTE TO THE CONSOLIDATED STATEMENT OF CASH FLOWS (Tables)	Network	*	*	http://www.cnoocltd.com/role/NoteToTheConsolidatedStatementOfCashFlowsTables
486	Implied Table	Table	*	*	implied:Table
487	NOTE TO THE CONSOLIDATED STATEMENT OF CASH FLOWS [abstract]	Abstract			ceo:NoteToConsolidatedStatementOfCashFlowsAbstract
488	Schedule of reconciliation of profit/(loss) before tax to cash generated from operations	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfReconciliationOfProfitLossBeforeTaxToCashGeneratedFromOperationsTableExplanatory
489	Schedule of of reconciliation of liabilities arising from financing activities	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesExplanatory
490	33203 - Disclosure - COMMITMENTS AND CONTINGENCIES (Tables)	Network	*	*	http://www.cnoocltd.com/role/CommitmentsAndContingenciesTables
491	Implied Table	Table	*	*	implied:Table
492	COMMITEMENTS AND CONTINGENCIES [abstract]	Abstract			ceo:DisclosureOfCommitmentsAndContingenciesAbstract
493	Schedule of capital commitments	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfCapitalCommitmentsTableExplanatory
494	Schedule of capital commitments of a joint venture	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfCapitalCommitmentsOfJointVenturesTableExplanatory
495	Schedule of total minimum lease payments under non-cancellable operating leases	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfMaturityAnalysisOfOperatingLeasePaymentsExplanatory
496	Schedule of office properties commitments of a joint venture	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfOfficePropertiesCommitmentsOfJointVentureTableExplanatory
497	Schedule of minimum lease payments under non-cancallable operating leases of plant and equipment	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfMinimumLeasePaymentsUnderNoncancallableOperatingLeasesOfPlantAndEquipmentTableExplanatory
498	33303 - Disclosure - FINANCIAL INSTRUMENTS (Tables)	Network	*	*	http://www.cnoocltd.com/role/FinancialInstrumentsTables
499	Implied Table	Table	*	*	implied:Table
500	FINANCIAL INSTRUMENTS [abstract]	Abstract			ifrs-full:DisclosureOfFinancialInstrumentsAbstract
501	Schedule of financial instruments measured at fair value for each hierarchy	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFairValueOfFinancialInstrumentsExplanatory
502	33403 - Disclosure - CONCENTRATION OF CUSTOMERS (Tables)	Network	*	*	http://www.cnoocltd.com/role/ConcentrationOfCustomersTables
503	Implied Table	Table	*	*	implied:Table
504	CONCENTRATION OF CUSTOMERS [abstract]	Abstract			ifrs-full:DisclosureOfMajorCustomersAbstract
505	Schedule of details of gross sales to top five third party customers	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfSegmentMajorCustomersTableExplanatory
506	33503 - Disclosure - FINANCIAL RISK MANAGEMENT OBJECTIVES AND POLICIES (Tables)	Network	*	*	http://www.cnoocltd.com/role/FinancialRiskManagementObjectivesAndPoliciesTables
507	Implied Table	Table	*	*	implied:Table
508	FINANCIAL RISK MANAGEMENT OBJECTIVES AND POLICIES [abstract]	Abstract			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsAbstract
509	Schedule of capital management on the basis of the debt to capital ratio	Concept (Text Block (HTML))	For Period		ceo:DisclosureOfCapitalManagementOnBasisOfDebtToCapitalRatioTableExplanatory
510	40101 - Disclosure - CORPORATE INFORMATION (Details)	Network	*	*	http://www.cnoocltd.com/role/CorporateInformationDetails
511	Disclosure of subsidiaries [table]	Table	*	*	ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesTable
512	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
513	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
514	Directly held subsidiaries [member]	Member			ceo:DirectlyHeldSubsidiariesMember
515	CNOOC China Limited [member]	Member			ceo:CnoocChinaLimitedMember
516	China Offshore Oil (Singapore) International Pte Ltd [member]	Member			ceo:ChinaOffshoreOilSingaporeInternationalPteLtdMember
517	CNOOC International Limited [member]	Member			ceo:CnoocInternationalLimitedMember
518	CNOOC Finance (2003) Limited [member]	Member			ceo:CnoocFinance2003LimitedMember
519	CNOOC Finance (2011) Limited [member]	Member			ceo:CnoocFinance2011LimitedMember
520	CNOOC Finance (2012) Limited [member]	Member			ceo:CnoocFinance2012LimitedMember
521	CNOOC Finance (2013) Limited [member]	Member			ceo:CnoocFinance2013LimitedMember
522	Indirectly held subsidiaries [member]	Member			ceo:IndirectlyHeldSubsidiariesMember
523	CNOOC Deepwater Development Limited [member]	Member			ceo:CnoocDeepwaterDevelopmentLimitedMember
524	CNOOC Southeast Asia Limited [member]	Member			ceo:CnoocSoutheastAsiaLimitedMember
525	CNOOC SES Ltd. [member]	Member			ceo:CnoocSesLtdMember
526	CNOOC Muturi Limited [member]	Member			ceo:CnoocMuturiLimitedMember
527	CNOOC NWS Private Limited [member]	Member			ceo:CnoocNwsPrivateLimitedMember
528	CNOOC Exploration & Production Nigeria Limited [member]	Member			ceo:CnoocExplorationAndProductionNigeriaLimitedMember
529	CNOOC Iraq Limited [member]	Member			ceo:CnoocIraqLimitedMember
530	CNOOC Canada Energy Ltd. [member]	Member			ceo:CnoocCanadaEnergyLtdMember
531	CNOOC Uganda Ltd [member]	Member			ceo:CnoocUgandaLtdMember
532	CNOOC Petroleum North America ULC [member]	Member			ceo:CnoocPetroleumNorthAmericaUlcMember
533	Nexen Petroleum U.K. Limited [member]	Member			ceo:NexenPetroleumUKLimitedMember
534	Nexen Petroleum Nigeria Limited [member]	Member			ceo:NexenPetroleumNigeriaLimitedMember
535	CNOOC Energy U.S.A. LLC [member]	Member			ceo:CnoocEnergyUsaLlcMember
536	Nexen Petroleum Offshore U.S.A. Inc. [member]	Member			ceo:NexenPetroleumOffshoreUSAIncMember
537	CNOOC Oil Sands Canada [member]	Member			ceo:CnoocOilSandsCanadaMember
538	CNOOC PETROLEUM BRASIL LTDA [member]	Member			ceo:CnoocPetroleumBrasilLtdaMember
539	CNOOC Nexen Finance (2014) ULC [member]	Member			ceo:CnoocNexenFinance2014UlcMember
540	CNOOC Finance (2015) U.S.A. LLC [member]	Member			ceo:CnoocFinance2015USALlcMember
541	CNOOC Finance (2015) Australia Pty Ltd [member]	Member			ceo:CnoocFinance2015AustraliaPtyLtdMember
542	Disclosure of subsidiaries [line items]	LineItems			ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesLineItems
543	Name of entity	Concept (Text/String)	For Period		ifrs-full:NameOfSubsidiary
544	Place of establishment	Concept (Text/String)	For Period		ifrs-full:CountryOfIncorporationOrResidenceOfSubsidiary
545	Nominal value of ordinary shares issued and paid-up/registered capital	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
546	Nominal value of ordinary shares issued and paid-up/registered capital (as a string)	Concept (Text/String)	For Period		ceo:NominalValueOfOrdinarySharesIssuedAndPaidupOrRegisteredCapital
547	Percentage of equity attributable to the Group	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInSubsidiary
548	Principal activities	Concept (Text/String)	For Period		ifrs-full:DescriptionOfNatureOfEntitysOperationsAndPrincipalActivities
549	40201 - Disclosure - CHANGES IN ACCOUNTING POLICIES AND DISCLOSURES - Impact on retained earnings (Details)	Network	*	*	http://www.cnoocltd.com/role/ChangesInAccountingPoliciesAndDisclosuresImpactOnRetainedEarningsDetails
550	Statement of changes in equity [table]	Table	*	*	ifrs-full:StatementOfChangesInEquityTable
551	Retrospective application and retrospective restatement [axis]	Axis			ifrs-full:RetrospectiveApplicationAndRetrospectiveRestatementAxis
552	Currently stated [member]	Member			ifrs-full:RestatedMember
553	Impact of IFRS 15/HKFRS 15 application [member]	Member			ifrs-full:IncreaseDecreaseDueToApplicationOfIFRS15Member
554	Retained earnings:	LineItems			ifrs-full:StatementOfChangesInEquityLineItems
555	The impact of overlifts or underlifts, net of tax	Concept (Monetary)	For Period	Debit	ceo:CumulativeEffectOnRetainedEarningsDueToImpactOfAdoptingNewAccountingPolicies
556	40202 - Disclosure - CHANGES IN ACCOUNTING POLICIES AND DISCLOSURES - Adjustments made to amounts recognized in the consolidated statement of financial position (Details)	Network	*	*	http://www.cnoocltd.com/role/ChangesInAccountingPoliciesAdjustmentsMadeToAmountsRecognizedInTheConsolidatedStatementOfFinancialPositionDetails
557	Disclosure of initial application of standards or interpretations [table]	Table	*	*	ifrs-full:DisclosureOfInitialApplicationOfStandardsOrInterpretationsTable
558	Retrospective application and retrospective restatement [axis]	Axis			ifrs-full:RetrospectiveApplicationAndRetrospectiveRestatementAxis
559	Currently stated [member]	Member			ifrs-full:RestatedMember
560	Reclassification [member]	Member			ceo:ReclassificationDueToApplicationOfIFRS15Member
561	Remeasurements [member]	Member			ifrs-full:IncreaseDecreaseDueToApplicationOfIFRS15Member
562	Disclosure of initial application of standards or interpretations [line items]	LineItems			ifrs-full:DisclosureOfInitialApplicationOfStandardsOrInterpretationsLineItems
563	CURRENT ASSETS [abstract]	Abstract			ifrs-full:CurrentAssetsAbstract
564	Trade receivables	Concept (Monetary)	As Of	Debit	ceo:TradeReceivablesTotal
565	NON-CURRENT ASSETS [abstract]	Abstract			ifrs-full:NoncurrentAssetsAbstract
566	Deferred tax assets	Concept (Monetary)	As Of	Debit	ifrs-full:NetDeferredTaxAssets
567	CURRENT LIABILITIES [abstract]	Abstract			ifrs-full:CurrentLiabilitiesAbstract
568	Contract liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentContractLiabilities
569	Other payables and accrued liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentAccruedExpensesAndOtherCurrentLiabilities
570	Taxes payable	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentTaxLiabilitiesCurrent
571	NON-CURRENT LIABILITIES [abstract]	Abstract			ifrs-full:NoncurrentLiabilitiesAbstract
572	Deferred tax liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NetDeferredTaxLiabilities
573	NET ASSETS	Concept (Monetary)	As Of	Debit	ifrs-full:NetAssetsLiabilities
574	40203 - Disclosure - CHANGES IN ACCOUNTING POLICIES AND DISCLOSURES - Impact on profit or loss and other comprehensive income (Details)	Network	*	*	http://www.cnoocltd.com/role/ChangesInAccountingPoliciesAndDisclosuresImpactOnProfitOrLossAndOtherComprehensiveIncomeDetails
575	Disclosure of initial application of standards or interpretations [table]	Table	*	*	ifrs-full:DisclosureOfInitialApplicationOfStandardsOrInterpretationsTable
576	Retrospective application and retrospective restatement [axis]	Axis			ifrs-full:RetrospectiveApplicationAndRetrospectiveRestatementAxis
577	Currently stated [member]	Member			ifrs-full:RestatedMember
578	Without application of IFRS 15/HKFRS 15 [member]	Member			ifrs-full:PreviouslyStatedMember
579	Impact of IFRS 15/HKFRS 15 application [member]	Member			ifrs-full:IncreaseDecreaseDueToApplicationOfIFRS15Member
580	Disclosure of initial application of standards or interpretations [line items]	LineItems			ifrs-full:DisclosureOfInitialApplicationOfStandardsOrInterpretationsLineItems
581	Revenue-Oil and gas sales	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromSaleOfOilAndGasProducts
582	Expenses [abstract]	Abstract			ifrs-full:ExpenseByNatureAbstract
583	Operating expenses	Concept (Monetary)	For Period	Debit	ifrs-full:OperatingExpense
584	Depreciation, depletion and amortization	Concept (Monetary)	For Period	Debit	ifrs-full:DepreciationAndAmortisationExpense
585	Profit before tax	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossBeforeTax
586	Income tax expense	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
587	PROFIT FOR THE YEAR ATTRIBUTABLE TO OWNERS OF THE PARENT	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossAttributableToOwnersOfParent
588	Total comprehensive income for the year attributable to owners of the parent	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncomeAttributableToOwnersOfParent
589	40204 - Disclosure - CHANGES IN ACCOUNTING POLICIES AND DISCLOSURES - Adjustments to financial Position (Details)	Network	*	*	http://www.cnoocltd.com/role/ChangesInAccountingPoliciesAndDisclosuresAdjustmentsToFinancialPositionDetails
590	Disclosure of initial application of standards or interpretations [table]	Table	*	*	ifrs-full:DisclosureOfInitialApplicationOfStandardsOrInterpretationsTable
591	Retrospective application and retrospective restatement [axis]	Axis			ifrs-full:RetrospectiveApplicationAndRetrospectiveRestatementAxis
592	Currently stated [member]	Member			ifrs-full:RestatedMember
593	Without application of IFRS 15/HKFRS 15 [member]	Member			ifrs-full:PreviouslyStatedMember
594	Impact of IFRS 15/HKFRS 15 application [member]	Member			ifrs-full:IncreaseDecreaseDueToApplicationOfIFRS15Member
595	Disclosure of initial application of standards or interpretations [line items]	LineItems			ifrs-full:DisclosureOfInitialApplicationOfStandardsOrInterpretationsLineItems
596	CURRENT ASSETS [abstract]	Abstract			ifrs-full:CurrentAssetsAbstract
597	Trade receivables	Concept (Monetary)	As Of	Debit	ceo:TradeReceivablesTotal
598	NON-CURRENT ASSETS [abstract]	Abstract			ifrs-full:NoncurrentAssetsAbstract
599	Deferred tax assets	Concept (Monetary)	As Of	Debit	ifrs-full:NetDeferredTaxAssets
600	CURRENT LIABILITIES [abstract]	Abstract			ifrs-full:CurrentLiabilitiesAbstract
601	Trade and accrued payables	Concept (Monetary)	As Of	Credit	ceo:TradeAndAccruedPayablesTotal
602	Contract liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentContractLiabilities
603	Other payables and accrued liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentAccruedExpensesAndOtherCurrentLiabilities
604	Taxes payable	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentTaxLiabilitiesCurrent
605	NON-CURRENT LIABILITIES [abstract]	Abstract			ifrs-full:NoncurrentLiabilitiesAbstract
606	Deferred tax liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NetDeferredTaxLiabilities
607	NET ASSETS	Concept (Monetary)	As Of	Debit	ifrs-full:NetAssetsLiabilities
608	40205 - Disclosure - CHANGES IN ACCOUNTING POLICIES AND DISCLOSURES - Impact on cash flows (Details)	Network	*	*	http://www.cnoocltd.com/role/ChangesInAccountingPoliciesAndDisclosuresImpactOnCashFlowsDetails
609	Disclosure of initial application of standards or interpretations [table]	Table	*	*	ifrs-full:DisclosureOfInitialApplicationOfStandardsOrInterpretationsTable
610	Retrospective application and retrospective restatement [axis]	Axis			ifrs-full:RetrospectiveApplicationAndRetrospectiveRestatementAxis
611	Currently stated [member]	Member			ifrs-full:RestatedMember
612	Without application of IFRS 15/HKFRS 15 [member]	Member			ifrs-full:PreviouslyStatedMember
613	Impact of IFRS 15/HKFRS 15 application [member]	Member			ifrs-full:IncreaseDecreaseDueToApplicationOfIFRS15Member
614	Disclosure of initial application of standards or interpretations [line items]	LineItems			ifrs-full:DisclosureOfInitialApplicationOfStandardsOrInterpretationsLineItems
615	OPERATING ACTIVITIES [abstract]	Abstract			ifrs-full:CashFlowsFromUsedInOperatingActivitiesAbstract
616	Profit before tax	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossBeforeTax
617	Adjustment for depreciation, depletion and amortization	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDepreciationAndAmortisationExpense
618	Increase in trade receivables and other current assets	Concept (Monetary)	For Period	Debit	ceo:AdjustmentsForDecreaseIncreaseInTradeReceivablesAndOtherCurrentAssets
619	Increase in trade and accrued payables, contract liabilities and other payables and accrued liabilities	Concept (Monetary)	For Period	Debit	ceo:AdjustmentsForDecreaseIncreaseInTradeAndOtherPayablesAccruedLiabilitiesContractLiabilities
620	Cash generated from operations	Concept (Monetary)	For Period		ifrs-full:CashFlowsFromUsedInOperations
621	40301 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Impairment of financial assets (Details)	Network	*	*	http://www.cnoocltd.com/role/SummaryOfSignificantAccountingPoliciesImpairmentOfFinancialAssetsDetails
622	Disclosure of impairment of financial assets [table]	Table	*	*	ceo:DisclosureOfImpairmentOfFinancialAssetsTable
623	Range [axis]	Axis			ifrs-full:RangeAxis
624	Ranges [member]	Member			ifrs-full:RangesMember
625	Maximum [member]	Member			ifrs-full:TopOfRangeMember
626	Minimum [member]	Member			ifrs-full:BottomOfRangeMember
627	Disclosure of impairment of financial assets [line items]	LineItems			ceo:DisclosureOfImpairmentOfFinancialAssetsLineItems
628	Period within which default events are possible, after the reporting date	Concept (xbrli:durationItemType)	For Period		ceo:PeriodOfPossibleDefaultEventsOfExpectedCreditLossAfterReportingDate
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630	40302 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Cash and cash equivalents (Details)	Network	*	*	http://www.cnoocltd.com/role/SummaryOfSignificantAccountingPoliciesCashAndCashEquivalentsDetails
631	Disclosure of cash and cash equivalents [table]	Table	*	*	ceo:DisclosureOfCashAndCashEquivalentsTable
632	Range [axis]	Axis			ifrs-full:RangeAxis
633	Ranges [member]	Member			ifrs-full:RangesMember
634	Maximum [member]	Member			ifrs-full:TopOfRangeMember
635	Disclosure of cash and cash equivalents [line items]	LineItems			ceo:DisclosureOfCashAndCashEquivalentsLineItems
636	Original maturity of short term deposits, classified as cash and cash equivalents	Concept (xbrli:durationItemType)	For Period		ceo:OriginalMaturityOfShortTermDepositsClassifiedAsCashAndCashEquivalents
637	40303 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Share-based payment transactions (Details)	Network	*	*	http://www.cnoocltd.com/role/SummaryOfSignificantAccountingPoliciesSharebasedPaymentTransactionsDetails
638	Implied Table	Table	*	*	implied:Table
639	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES [abstract]	Abstract			ceo:SummaryOfSignificantAccountingPoliciesAbstract
640	Expense recognized for awards that do not ultimately vest for the Group	Concept (Monetary)	For Period	Debit	ceo:AwardsExpenseNotUltimatelyVestForGroup
641	Equity-settled award, cancelled or modified, in share-based payment transactions	Concept (Monetary)	For Period	Debit	ceo:EquitysettledAwardCancelledOrModifiedInSharebasedPaymentTransactions
642	40401 - Disclosure - OIL AND GAS SALES AND MARKETING REVENUES (Details)	Network	*	*	http://www.cnoocltd.com/role/OilAndGasSalesAndMarketingRevenuesDetails
643	Disclosure of detailed information about oil and gas sales and marketing revenues [table]	Table	*	*	ceo:DisclosureOfDetailedInformationAboutOilAndGasSalesAndMarketingRevenuesTable
644	Range [axis]	Axis			ifrs-full:RangeAxis
645	Ranges [member]	Member			ifrs-full:RangesMember
646	Maximum [member]	Member			ifrs-full:TopOfRangeMember
647	Disclosure of detailed information about oil and gas sales and marketing revenues [line items]	LineItems			ceo:DisclosureOfDetailedInformationAboutOilAndGasSalesAndMarketingRevenuesLineItems
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649	Less: Royalties	Concept (Monetary)	For Period	Debit	ifrs-full:RoyaltyExpense
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651	Oil and gas sales	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromSaleOfOilAndGasProducts
652	Marketing revenues	Concept (Monetary)	For Period	Credit	ceo:RevenueFromMarketing
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654	Period between payment and transfer of associated goods	Concept (xbrli:durationItemType)	For Period		ceo:PeriodBetweenPaymentAndTransferOfAssociatedGoods
655	40501 - Disclosure - SEGMENT INFORMATION - Segment results (Details)	Network	*	*	http://www.cnoocltd.com/role/SegmentInformationSegmentResultsDetails
656	Disclosure of operating segments [table]	Table	*	*	ifrs-full:DisclosureOfOperatingSegmentsTable
657	Segment consolidation items [axis]	Axis			ifrs-full:SegmentConsolidationItemsAxis
658	Entity's total for segment consolidation items [member]	Member			ifrs-full:EntitysTotalForSegmentConsolidationItemsMember
659	Operating segments [member]	Member			ifrs-full:OperatingSegmentsMember
660	E&P [member]	Member			ceo:ExplorationAndProductionSegmentMember
661	Trading business [member]	Member			ceo:TradingBusinessSegmentMember
662	Corporate [member]	Member			ceo:CorporateSegmentMember
663	Material reconciling items [member]	Member			ifrs-full:MaterialReconcilingItemsMember
664	Eliminations [member]	Member			ifrs-full:EliminationOfIntersegmentAmountsMember
665	Disclosure of operating segments [line items]	LineItems			ifrs-full:DisclosureOfOperatingSegmentsLineItems
666	External revenue	Concept (Monetary)	For Period	Credit	ceo:ExternalRevenue
667	Intersegment revenue	Concept (Monetary)	For Period	Credit	ceo:IntersegmentRevenue
668	Total revenue	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
669	Segment profit for the year	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
670	Amounts included in the measure of segment profit or loss	Abstract			ceo:AmountsIncludedInMeasureOfSegmentProfitOrLossAbstract
671	Operating expenses	Concept (Monetary)	For Period	Debit	ifrs-full:OperatingExpense
672	Taxes other than income tax	Concept (Monetary)	For Period	Debit	ifrs-full:TaxExpenseOtherThanIncomeTaxExpense
673	Exploration expenses	Concept (Monetary)	For Period	Debit	ifrs-full:ExpenseArisingFromExplorationForAndEvaluationOfMineralResources
674	Depreciation, depletion and amortization	Concept (Monetary)	For Period	Debit	ifrs-full:DepreciationAndAmortisationExpense
675	Impairment and provision	Concept (Monetary)	For Period	Debit	ifrs-full:ImpairmentLossRecognisedInProfitOrLoss
676	Selling and administrative expenses	Concept (Monetary)	For Period	Debit	ifrs-full:SellingGeneralAndAdministrativeExpense
677	Interest income	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromInterest
678	Finance costs	Concept (Monetary)	For Period	Debit	ifrs-full:FinanceCosts
679	Share of profits of associates and profit/(loss) attributable to a joint venture	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfProfitLossOfAssociatesAndJointVenturesAccountedForUsingEquityMethod
680	Income tax credit/(expense)	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
681	Other segment information	Abstract			ceo:OtherSegmentInformationAbstract
682	Investments in associates and a joint venture	Concept (Monetary)	As Of	Debit	ifrs-full:InvestmentAccountedForUsingEquityMethod
683	Others	Concept (Monetary)	As Of	Debit	ifrs-full:OtherAssets
684	Segment assets	Concept (Monetary)	As Of	Debit	ifrs-full:Assets
685	Segment liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:Liabilities
686	Capital expenditure	Concept (Monetary)	For Period	Debit	ceo:CapitalExpenditure
687	40502 - Disclosure - SEGMENT INFORMATION - Geographical information (Details)	Network	*	*	http://www.cnoocltd.com/role/SegmentInformationGeographicalInformationDetails
688	Disclosure of geographical areas [table]	Table	*	*	ifrs-full:DisclosureOfGeographicalAreasTable
689	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
690	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
691	PRC [member]	Member			ifrs-full:CountryOfDomicileMember
692	Other locations [member]	Member			ifrs-full:ForeignCountriesMember
693	Canada [member]	Member			country:CA
694	Others [member]	Member			ceo:OtherForeignCountriesMember
695	Range [axis]	Axis			ifrs-full:RangeAxis
696	Ranges [member]	Member			ifrs-full:RangesMember
697	Maximum [member]	Member			ifrs-full:TopOfRangeMember
698	Disclosure of geographical areas [line items]	LineItems			ifrs-full:DisclosureOfGeographicalAreasLineItems
699	Ratio of revenue from customers in different locations to Group's revenues	Concept (Percent)	For Period		ceo:RatioOfRevenueFromCustomersInDifferentLocationsToGroupsRevenues
700	Property, plant and equipment	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
701	Investments in associates and a joint venture	Concept (Monetary)	As Of	Debit	ifrs-full:InvestmentAccountedForUsingEquityMethod
702	Other non-current assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherNoncurrentAssets
703	40503 - Disclosure - SEGMENT INFORMATION - Information about major customers (Details)	Network	*	*	http://www.cnoocltd.com/role/SegmentInformationInformationAboutMajorCustomersDetails
704	Disclosure of major customers [table]	Table	*	*	ifrs-full:DisclosureOfMajorCustomersTable
705	Major customers [axis]	Axis			ifrs-full:MajorCustomersAxis
706	Customers [member]	Member			ifrs-full:MajorCustomersMember
707	PetroChina Company Limited [member]	Member			ceo:PetrochinaCompanyLimitedMember
708	Segment consolidation items [axis]	Axis			ifrs-full:SegmentConsolidationItemsAxis
709	Entity's total for segment consolidation items [member]	Member			ifrs-full:EntitysTotalForSegmentConsolidationItemsMember
710	The E&P segment and the trading business segment [member]	Member			ceo:ExplorationAndProductionSegmentAndTradingBusinessSegmentMember
711	Disclosure of major customers [line items]	LineItems			ifrs-full:DisclosureOfMajorCustomersLineItems
712	Revenue	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
713	40601 - Disclosure - PROFIT BEFORE TAX (Details)	Network	*	*	http://www.cnoocltd.com/role/ProfitBeforeTaxDetails
714	Implied Table	Table	*	*	implied:Table
715	PROFIT BEFORE TAX [abstract]	Abstract			ceo:ProfitBeforeTaxAbstract
716	Crediting:	Abstract			ceo:CreditingAdjustmentForCalculatingProfitLossBeforeTaxAbstract
717	Interest income from bank deposits	Concept (Monetary)	For Period	Credit	ifrs-full:InterestIncomeOnDeposits
718	Investment income:	Abstract			ceo:InvestmentIncomeAbstract
719	Fair value changes on other financial assets	Concept (Monetary)	For Period	Credit	ifrs-full:InvestmentIncome
720	Insurance compensation on disposal of property, plant and equipment	Concept (Monetary)	For Period	Credit	ceo:InsuranceCompensationOnDisposalOfPropertyPlantAndEquipment
721	Charging:	Abstract			ceo:ChargingAdjustmentForCalculatingProfitLossBeforeTaxAbstract
722	Auditors' remuneration:	Abstract			ifrs-full:AuditorsRemunerationAbstract
723	Audit fee	Concept (Monetary)	For Period	Debit	ifrs-full:AuditorsRemunerationForAuditServices
724	Other fees	Concept (Monetary)	For Period	Debit	ifrs-full:AuditorsRemunerationForOtherServices
725	Auditors' remuneration	Concept (Monetary)	For Period	Debit	ifrs-full:AuditorsRemuneration
726	Employee wages, salaries, allowances and social security costs	Concept (Monetary)	For Period	Debit	ifrs-full:EmployeeBenefitsExpense
727	Impairment and provision:	Abstract			ifrs-full:DisclosureOfImpairmentLossAndReversalOfImpairmentLossAbstract
728	Property, plant and equipment	Concept (Monetary)	For Period		ifrs-full:ImpairmentLossRecognisedInProfitOrLossPropertyPlantAndEquipment
729	Trade receivables	Concept (Monetary)	For Period	Debit	ifrs-full:ImpairmentLossReversalOfImpairmentLossRecognisedInProfitOrLossTradeReceivables
730	Others	Concept (Monetary)	For Period	Debit	ceo:ImpairmentLossRecognisedInProfitOrLossOthers
731	Total impairment and provision	Concept (Monetary)	For Period	Debit	ifrs-full:ImpairmentLossRecognisedInProfitOrLoss
732	Depreciation, depletion and amortization:	Abstract			ifrs-full:DepreciationAndAmortisationExpenseAbstract
733	Property, plant and equipment	Concept (Monetary)	For Period		ifrs-full:DepreciationPropertyPlantAndEquipment
734	Intangible assets	Concept (Monetary)	For Period		ifrs-full:AmortisationIntangibleAssetsOtherThanGoodwill
735	Less: Net amount capitalized	Concept (Monetary)	For Period	Credit	ceo:DepreciationDepletionAndAmortizationExpensesCapitalized
736	Total depreciation, depletion and amortization	Concept (Monetary)	For Period	Debit	ifrs-full:DepreciationAndAmortisationExpense
737	Operating lease rentals:	Abstract			ifrs-full:LeaseAndSubleasePaymentsRecognisedAsExpenseAbstract
738	Office properties	Concept (Monetary)	For Period	Debit	ceo:RentalExpensesOfOfficeProperties
739	Plant and equipment	Concept (Monetary)	For Period	Debit	ceo:RentalExpensesOfPlantAndEquipment
740	Operating lease rentals	Concept (Monetary)	For Period	Debit	ifrs-full:RentalExpense
741	Repairs and maintenance	Concept (Monetary)	For Period	Debit	ifrs-full:RepairsAndMaintenanceExpense
742	Research and development costs	Concept (Monetary)	For Period	Debit	ifrs-full:ResearchAndDevelopmentExpense
743	Loss on disposal of property, plant and equipment	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnDisposalsOfPropertyPlantAndEquipment
744	40701 - Disclosure - FINANCE COSTS (Details)	Network	*	*	http://www.cnoocltd.com/role/FinanceCostsDetails
745	Implied Table	Table	*	*	implied:Table
746	FINANCE COSTS [abstract]	Abstract			ifrs-full:BorrowingCostsAbstract
747	Interest on bank loans	Concept (Monetary)	For Period	Debit	ifrs-full:InterestExpenseOnBankLoansAndOverdrafts
748	Interest on other loans	Concept (Monetary)	For Period	Debit	ifrs-full:InterestExpenseOnOtherFinancialLiabilities
749	Other borrowing costs	Concept (Monetary)	For Period	Debit	ifrs-full:InterestExpenseOnBorrowings
750	Total borrowing costs	Concept (Monetary)	For Period		ifrs-full:BorrowingCostsIncurred
751	Less: Amount capitalized in property, plant and equipment (note 13)	Concept (Monetary)	For Period		ifrs-full:BorrowingCostsCapitalised
752	Borrowing costs recognised as expense	Concept (Monetary)	For Period	Debit	ifrs-full:BorrowingCostsRecognisedAsExpense
753	Other finance costs:	Abstract			ceo:OtherFinanceCostsAbstract
754	Unwinding of discount on provision for dismantlement (note 26)	Concept (Monetary)	For Period	Debit	ifrs-full:ExpenseDueToUnwindingOfDiscountOnProvisions
755	Total finance costs	Concept (Monetary)	For Period	Debit	ifrs-full:FinanceCosts
756	40702 - Disclosure - FINANCE COSTS - Narrative (Details)	Network	*	*	http://www.cnoocltd.com/role/FinanceCostsNarrativeDetails
757	Disclosure of detailed information about finance costs [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
758	Range [axis]	Axis			ifrs-full:RangeAxis
759	Ranges [member]	Member			ifrs-full:RangesMember
760	Minimum [member]	Member			ifrs-full:BottomOfRangeMember
761	Maximum [member]	Member			ifrs-full:TopOfRangeMember
762	Disclosure of detailed information about finance costs [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
763	Effective interest rates used to determine the amount of related borrowing costs for capitalization	Concept (Percent)	For Period		ifrs-full:CapitalisationRateOfBorrowingCostsEligibleForCapitalisation
764	40801 - Disclosure - KEY MANAGEMENT PERSONNEL'S REMUNERATION - Directors' remuneration (Details)	Network	*	*	http://www.cnoocltd.com/role/KeyManagementPersonnelsRemunerationDirectorsRemunerationDetails
765	Disclosure of transactions between related parties [table]	Table	*	*	ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesTable
766	Categories of related parties [axis]	Axis			ifrs-full:CategoriesOfRelatedPartiesAxis
767	Entity's total for related parties [member]	Member			ifrs-full:EntitysTotalForRelatedPartiesMember
768	Directors [member]	Member			ceo:IfrsDirectorMember
769	Executive directors [member]	Member			ceo:ExecutiveDirectorsMember
770	Non-executive directors [member]	Member			ceo:NonexecutiveDirectorsMember
771	Independent non-executive directors [member]	Member			ceo:IndependentNonexecutiveDirectorsMember
772	Name of employees [axis]	Axis			ceo:NameOfEmployeesAxis
773	Name of employees [member]	Member			ceo:NameOfEmployeesMember
774	Yang Hua [member]	Member			ceo:YangHuaMember
775	Yuan Guangyu [member]	Member			ceo:YuanGuangyuMember
776	Li Fanrong [member]	Member			ceo:LiFanrongMember
777	Liu Jian [member]	Member			ceo:LiuJianMember
778	Wu Guangqi [member]	Member			ceo:WuGuangqiMember
779	Lv Bo [member]	Member			ceo:LvBoMember
780	Chiu Sung Hong [member]	Member			ceo:ChiuSungHongMember
781	Lawrence J. Lau [member]	Member			ceo:LawrenceJLauMember
782	Tse Hau Yin, Aloysius [member]	Member			ceo:TseHauYinAloysiusMember
783	Kevin G. Lynch [member]	Member			ceo:KevinGLynchMember
784	Xu Keqiang [member]	Member			ceo:XuKeqiangMember
785	Wang Dongjin [member]	Member			ceo:WangDongjinMember
786	Disclosure of transactions between related parties [line items]	LineItems			ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesLineItems
787	Fees	Concept (Monetary)	For Period	Debit	ceo:FeesPaidOrPayableToEmployees
788	Salaries, allowances and benefits in kind	Concept (Monetary)	For Period	Debit	ifrs-full:WagesAndSalaries
789	Performance related bonuses	Concept (Monetary)	For Period	Debit	ceo:PerformanceRelatedBonuses
790	Pension scheme contributions	Concept (Monetary)	For Period	Debit	ifrs-full:PostemploymentBenefitExpenseDefinedContributionPlans
791	Total paid/payable during the year	Concept (Monetary)	For Period	Debit	ifrs-full:DirectorsRemunerationExpense
792	Number of directors exercised any share option	Concept (Decimal)	For Period		ifrs-full:NumberOfShareOptionsExercisedInSharebasedPaymentArrangement
793	Number of new share option was granted to Directors in respect of their services to the Group under the applicable share option schemes of the Company	Concept (Decimal)	For Period		ifrs-full:NumberOfShareOptionsGrantedInSharebasedPaymentArrangement
794	40802 - Disclosure - KEY MANAGEMENT PERSONNEL'S REMUNERATION - Other key management personnel's (excluding Directors') remuneration (Details)	Network	*	*	http://www.cnoocltd.com/role/KeyManagementPersonnelsRemunerationOtherKeyManagementPersonnelsExcludingDirectorsRemunerationDetails
795	Disclosure of transactions between related parties [table]	Table	*	*	ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesTable
796	Categories of related parties [axis]	Axis			ifrs-full:CategoriesOfRelatedPartiesAxis
797	Entity's total for related parties [member]	Member			ifrs-full:EntitysTotalForRelatedPartiesMember
798	Other key management personnel (excluding Directors) [member]	Member			ceo:OtherKeyManagementPersonnelExcludingDirectorsMember
799	Range [axis]	Axis			ifrs-full:RangeAxis
800	Ranges [member]	Member			ifrs-full:RangesMember
801	Nil to RMB 2,000,000 [member]	Member			ceo:ZeroToRmbTwoMillionMember
802	Disclosure of transactions between related parties [line items]	LineItems			ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesLineItems
803	Short term employee benefits	Concept (Monetary)	For Period	Debit	ifrs-full:ShorttermEmployeeBenefitsExpense
804	Pension scheme contributions	Concept (Monetary)	For Period	Debit	ifrs-full:PostemploymentBenefitExpenseDefinedContributionPlans
805	Amount paid/payable during the year	Concept (Monetary)	For Period	Debit	ifrs-full:EmployeeBenefitsExpense
806	Number of employees	Concept (Decimal)	As Of		ifrs-full:NumberOfEmployees
807	40901 - Disclosure - FIVE HIGHEST PAID EMPLOYEES - Details of remuneration (Details)	Network	*	*	http://www.cnoocltd.com/role/FiveHighestPaidEmployeesDetailsOfRemunerationDetails
808	Disclosure Of Highest Paid Employees [Table]	Table	*	*	ceo:DisclosureOfHighestPaidEmployeesTable
809	Counterparties [axis]	Axis			ifrs-full:CounterpartiesAxis
810	Counterparties [member]	Member			ifrs-full:CounterpartiesMember
811	Highest paid employees [member]	Member			ceo:HighestPaidEmployeesMember
812	Disclosure Of Highest Paid Employees [line items]	LineItems			ceo:DisclosureOfHighestPaidEmployeesLineItems
813	Number of Directors who received an amount which falls within the category of the five highest paid employees	Concept (Decimal)	As Of		ceo:NumberOfDirectorsWhoseRemunerationFallingWithinCategoryOfFiveHighestPaidEmployees
814	Number of highest paid employees	Concept (Decimal)	As Of		ifrs-full:NumberOfEmployees
815	Salaries, allowances and benefits in kind	Concept (Monetary)	For Period	Debit	ifrs-full:WagesAndSalaries
816	Performance-related bonuses	Concept (Monetary)	For Period	Debit	ceo:PerformanceRelatedBonuses
817	Pension scheme contributions	Concept (Monetary)	For Period	Debit	ifrs-full:PostemploymentBenefitExpenseDefinedContributionPlans
818	Amount paid/payable during the year	Concept (Monetary)	For Period	Debit	ifrs-full:EmployeeBenefitsExpense
819	40902 - Disclosure - FIVE HIGHEST PAID EMPLOYEES - Number of highest paid employees in each remuneration band (Details)	Network	*	*	http://www.cnoocltd.com/role/FiveHighestPaidEmployeesNumberOfHighestPaidEmployeesInEachRemunerationBandDetails
820	Disclosure Of Highest Paid Employees [Table]	Table	*	*	ceo:DisclosureOfHighestPaidEmployeesTable
821	Counterparties [axis]	Axis			ifrs-full:CounterpartiesAxis
822	Counterparties [member]	Member			ifrs-full:CounterpartiesMember
823	Highest paid employees [member]	Member			ceo:HighestPaidEmployeesMember
824	Range [axis]	Axis			ifrs-full:RangeAxis
825	Ranges [member]	Member			ifrs-full:RangesMember
826	RMB5,500,001 - RMB6,000,000 [member]	Member			ceo:HighestPaidEmployeesRangeOneMember
827	RMB6,000,001 - RMB6,500,000 [member]	Member			ceo:HighestPaidEmployeesRangeTwoMember
828	RMB6,500,001 - RMB7,000,000 [member]	Member			ceo:HighestPaidEmployeesRangeThreeMember
829	RMB7,000,001 - RMB7,500,000 [member]	Member			ceo:HighestPaidEmployeesRangeFourMember
830	RMB7,500,001 - RMB8,000,000 [member]	Member			ceo:HighestPaidEmployeesRangeFiveMember
831	RMB8,000,001 - RMB8,500,000 [member]	Member			ceo:HighestPaidEmployeesRangeSixMember
832	RMB8,500,001 - RMB9,000,000 [member]	Member			ceo:HighestPaidEmployeesRangeSevenMember
833	RMB9,000,001 - RMB9,500,000 [member]	Member			ceo:HighestPaidEmployeesRangeEightMember
834	RMB10,000,001 - RMB10,500,000 [member]	Member			ceo:HighestPaidEmployeesRangeNineMember
835	RMB10,500,001 - RMB11,000,000 [member]	Member			ceo:HighestPaidEmployeesRangeTenMember
836	Disclosure Of Highest Paid Employees [line items]	LineItems			ceo:DisclosureOfHighestPaidEmployeesLineItems
837	Number of employees	Concept (Decimal)	As Of		ifrs-full:NumberOfEmployees
838	41001 - Disclosure - TAX - Income tax - Narrative (Details)	Network	*	*	http://www.cnoocltd.com/role/TaxIncomeTax
839	Disclosure of detailed information about income tax rate [table]	Table	*	*	ceo:DisclosureOfDetailedInformationAboutIncomeTaxRateTable
840	Range [axis]	Axis			ifrs-full:RangeAxis
841	Ranges [member]	Member			ifrs-full:RangesMember
842	Maximum [member]	Member			ifrs-full:TopOfRangeMember
843	Minimum [member]	Member			ifrs-full:BottomOfRangeMember
844	All countries [axis]	Axis			ceo:AllCountriesAxis
845	All countries [domain]	Member			country:AllCountriesDomain
846	Hong Kong [member]	Member			country:HK
847	PRC [member]	Member			country:CN
848	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
849	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
850	Outside the PRC [member]	Member			ifrs-full:ForeignCountriesMember
851	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
852	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
853	CNOOC China Limited [member]	Member			ceo:CnoocChinaLimitedMember
854	CNOOC Deepwater Development Limited [member]	Member			ceo:CnoocDeepwaterDevelopmentLimitedMember
855	Entity Classifications Sector and Entity [Axis]	Axis			ceo:EntityClassificationsSectorAndEntityAxis
856	Sector And Entity [member]	Member			ceo:SectorAndEntityMember
857	High and new technology enterprise [member]	Member			ceo:HighAndNewTechnologyEnterpriseMember
858	Disclosure of detailed information about income tax rate [line items]	LineItems			ceo:DisclosureOfDetailedInformationAboutIncomeTaxRateLineItems
859	Income tax rate	Concept (Percent)	For Period		ifrs-full:ApplicableTaxRate
860	41002 - Disclosure - TAX - Analysis of tax (credit)/expense in the Group's consolidated statement of profit or loss and other comprehensive income (Details)	Network	*	*	http://www.cnoocltd.com/role/TaxAnalysisOfTaxCreditExpenseInTheGroupsConsolidatedStatementOfProfitOrLossAndOtherComprehensiveIncomeDetails
861	Disclosure of detailed information about analysis of tax expense/(credit) in consolidated statement of profit or loss and other comprehensive income [table]	Table	*	*	ceo:DisclosureOfDetailedInformationAboutAnalysisOfTaxExpenseCreditInConsolidatedStatementOfProfitOrLossAndOtherComprehensiveIncomeTable
862	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
863	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
864	PRC [member]	Member			ifrs-full:CountryOfDomicileMember
865	Outside the PRC [member]	Member			ifrs-full:ForeignCountriesMember
866	Disclosure of detailed information about analysis of tax expense/ (credit) in consolidated statement of profit or loss and other comprehensive income [line items]	LineItems			ceo:DisclosureOfDetailedInformationAboutAnalysisOfTaxExpenseCreditInConsolidatedStatementOfProfitOrLossAndOtherComprehensiveIncomeLineItems
867	Current tax	Abstract			ceo:CurrentTaxExpenseIncomeAbstract
868	Provision for enterprise income tax on the estimated taxable profits for the year	Concept (Monetary)	For Period	Debit	ifrs-full:CurrentTaxExpenseIncome
869	Deferred tax	Abstract			ifrs-full:DeferredTaxExpenseIncomeAbstract
870	Temporary differences in the current year	Concept (Monetary)	For Period		ifrs-full:DeferredTaxExpenseIncomeRecognisedInProfitOrLoss
871	Effect of changes in tax rates	Concept (Monetary)	For Period	Debit	ifrs-full:DeferredTaxExpenseIncomeRelatingToTaxRateChangesOrImpositionOfNewTaxes
872	Income tax (credit)/expense for the year	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
873	41003 - Disclosure - TAX - Reconciliation of the PRC statutory corporate income tax rate to the effective income tax rate (Details)	Network	*	*	http://www.cnoocltd.com/role/TaxReconciliationOfThePrcStatutoryCorporateIncomeTaxRateToTheEffectiveIncomeTaxRateDetails
874	Implied Table	Table	*	*	implied:Table
875	TAX [abstract]	Abstract			ifrs-full:MajorComponentsOfTaxExpenseIncomeAbstract
876	PRC statutory enterprise income tax rate	Concept (Percent)	For Period		ifrs-full:ApplicableTaxRate
877	Effect of different tax rates for overseas subsidiaries	Concept (Percent)	For Period		ifrs-full:TaxRateEffectOfForeignTaxRates
878	Effect of changes in tax rates	Concept (Percent)	For Period		ifrs-full:TaxRateEffectFromChangeInTaxRate
879	Tax credit from the government	Concept (Percent)	For Period		ceo:TaxRateEffectOfTaxCreditFromGovernment
880	Tax reported in equity-accounted entities in China	Concept (Percent)	For Period		ceo:TaxRateEffectOfTaxReportedInEquityaccountedEntities
881	Tax losses previously not recognized	Concept (Percent)	For Period		ifrs-full:TaxRateEffectOfTaxLosses
882	Others	Concept (Percent)	For Period		ifrs-full:OtherTaxRateEffectsForReconciliationBetweenAccountingProfitAndTaxExpenseIncome
883	Group's effective income tax rate	Concept (Percent)	For Period		ifrs-full:AverageEffectiveTaxRate
884	41004 - Disclosure - TAX - Movements of deferred tax liabilities net of deferred tax assets (Details)	Network	*	*	http://www.cnoocltd.com/role/TaxMovementsOfDeferredTaxLiabilitiesNetOfDeferredTaxAssetsDetails
885	Implied Table	Table	*	*	implied:Table
886	TAX [abstract]	Abstract			ifrs-full:MajorComponentsOfTaxExpenseIncomeAbstract
887	Balance at beginning of period	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredTaxLiabilityAsset
888	Credit to the profit or loss	Concept (Monetary)	For Period		ifrs-full:DeferredTaxExpenseIncomeRecognisedInProfitOrLoss
889	Change in tax rates	Concept (Monetary)	For Period	Debit	ifrs-full:DeferredTaxExpenseIncomeRelatingToTaxRateChangesOrImpositionOfNewTaxes
890	Charge to other comprehensive income	Concept (Monetary)	For Period		ifrs-full:IncomeTaxRelatingToComponentsOfOtherComprehensiveIncome
891	Exchange differences	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughNetExchangeDifferencesDeferredTaxLiabilityAsset
892	Balance at end of period	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredTaxLiabilityAsset
893	41005 - Disclosure - TAX - Principal components of deferred tax balances (Details)	Network	*	*	http://www.cnoocltd.com/role/TaxPrincipalComponentsOfDeferredTaxBalancesDetails
894	Disclosure of temporary difference, unused tax losses and unused tax credits [table]	Table	*	*	ifrs-full:DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsTable
895	Temporary difference, unused tax losses and unused tax credits [axis]	Axis			ifrs-full:TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis
896	Temporary difference, unused tax losses and unused tax credits [member]	Member			ifrs-full:TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsMember
897	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
898	Provision for dismantlement [member]	Member			ifrs-full:ProvisionForDecommissioningRestorationAndRehabilitationCostsMember
899	Losses available for offsetting against future taxable profit [member]	Member			ifrs-full:UnusedTaxLossesMember
900	Fair value of long term borrowings [member]	Member			ceo:FairValueOfLongTermBorrowingsMember
901	Fair value changes on other financial assets [member]	Member			ceo:FairValueChangesOnOtherFinancialAssetsMember
902	Others [member]	Member			ifrs-full:OtherTemporaryDifferencesMember
903	Range [axis]	Axis			ifrs-full:RangeAxis
904	Ranges [member]	Member			ifrs-full:RangesMember
905	Maximum [member]	Member			ifrs-full:TopOfRangeMember
906	Minimum [member]	Member			ifrs-full:BottomOfRangeMember
907	All countries [axis]	Axis			ceo:AllCountriesAxis
908	All countries [domain]	Member			country:AllCountriesDomain
909	US	Member			country:US
910	Canada [member]	Member			country:CA
911	Uganda [member]	Member			country:UG
912	Countries excluding UG [member]	Member			ceo:CountriesExcludingUgMember
913	Nigeria [member]	Member			country:NG
914	Countries excluding NG [member]	Member			ceo:CountriesExcludingNgMember
915	Disclosure of temporary difference, unused tax losses and unused tax credits [line items]	LineItems			ifrs-full:DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems
916	Deferred tax assets	Concept (Monetary)	As Of	Debit	ifrs-full:DeferredTaxAssets
917	Deferred tax liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredTaxLiabilities
918	Net deferred tax assets	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredTaxLiabilityAsset
919	Of which - deferred tax assets	Concept (Monetary)	As Of	Debit	ifrs-full:NetDeferredTaxAssets
920	Of which - deferred tax liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NetDeferredTaxLiabilities
921	Carry-forward tax losses	Concept (Monetary)	For Period	Debit	ceo:CarryforwardTaxLossesAvailableToOffsetAgainstFutureTaxableProfits
922	Expiry date	Concept (Text/String)	For Period		ifrs-full:DescriptionOfExpiryDateOfTemporaryDifferencesUnusedTaxLossesAndUnusedTaxCredits
923	Tax losses	Concept (Monetary)	For Period	Debit	ceo:TaxLossesToRecognizeDeferredTaxAssets
924	Unrecognized tax losses	Concept (Monetary)	As Of		ifrs-full:UnusedTaxLossesForWhichNoDeferredTaxAssetRecognised
925	Unused tax credits	Concept (Monetary)	As Of		ifrs-full:UnusedTaxCreditsForWhichNoDeferredTaxAssetRecognised
926	41006 - Disclosure - TAX - Other taxes (Details)	Network	*	*	http://www.cnoocltd.com/role/TaxOtherTaxesDetails
927	Disclosure of detailed information about taxes other than income tax [table]	Table	*	*	ceo:DisclosureOfDetailedInformationAboutTaxesOtherThanIncomeTaxTable
928	Range [axis]	Axis			ifrs-full:RangeAxis
929	Ranges [member]	Member			ifrs-full:RangesMember
930	Maximum [member]	Member			ifrs-full:TopOfRangeMember
931	Minimum [member]	Member			ifrs-full:BottomOfRangeMember
932	Types of rate-regulated activities [axis]	Axis			ifrs-full:TypesOfRateregulatedActivitiesAxis
933	Rate-regulated activities [member]	Member			ifrs-full:RateregulatedActivitiesMember
934	Oil and gas sale activities [member]	Member			ceo:OilAndGasSaleActivitiesMember
935	Gas sales [member]	Member			ifrs-full:GasDistributionMember
936	Disclosure of detailed information about taxes other than income tax [line items]	LineItems			ceo:DisclosureOfDetailedInformationAboutTaxesOtherThanIncomeTaxLineItems
937	Production tax rate	Concept (Percent)	For Period		ceo:ProductionTaxRate
938	VAT rate	Concept (Percent)	For Period		ceo:ValueAddedTaxRate
939	Resource tax rate	Concept (Percent)	For Period		ceo:ResourceTaxRate
940	Export tariff rate	Concept (Percent)	For Period		ceo:ExportTariffRate
941	City construction tax rate lower	Concept (Percent)	For Period		ceo:CityConstructionTaxRateLower
942	City construction tax rate higher	Concept (Percent)	For Period		ceo:CityConstructionTaxRateHigher
943	Educational surcharge rate	Concept (Percent)	For Period		ceo:EducationalSurchargeRate
944	Local educational surcharge rate	Concept (Percent)	For Period		ceo:LocalEducationalSurchargeRate
945	41007 - Disclosure - TAX - Special Oil Gain Levy (Details)	Network	*	*	http://www.cnoocltd.com/role/TaxSpecialOilGainLevyDetails
946	Disclosure of detailed information about special oil gain levy [table]	Table	*	*	ceo:DisclosureOfDetailedInformationAboutSpecialOilGainLevyTable
947	Range [axis]	Axis			ifrs-full:RangeAxis
948	Ranges [member]	Member			ifrs-full:RangesMember
949	Maximum [member]	Member			ifrs-full:TopOfRangeMember
950	Minimum [member]	Member			ifrs-full:BottomOfRangeMember
951	Disclosure of detailed information about special oil gain levy [line items]	LineItems			ceo:DisclosureOfDetailedInformationAboutSpecialOilGainLevyLineItems
952	Progressive rates	Concept (Percent)	For Period		ceo:ProgressiveRateOfSpecialOilGainLevy
953	Threshold of Special Oil Gain Levy	Concept (Decimal)	For Period		ceo:ThresholdOfSpecialOilGainLevyMeasuredInTermsOfMonthlyWeightedAverageSalesPriceOfCrudeOil
954	Number of Special Oil Gain Levy levels	Concept (Integer)	As Of		ceo:NumberOfSpecialOilGainLevyLevels
955	41101 - Disclosure - EARNINGS PER SHARE (Details)	Network	*	*	http://www.cnoocltd.com/role/EarningsPerShareDetails
956	Implied Table	Table	*	*	implied:Table
957	EARNINGS PER SHARE [abstract]	Abstract			ifrs-full:EarningsPerShareAbstract
958	Earnings:	Abstract			ifrs-full:ProfitLossAbstract
959	Profit for the purpose of basic and diluted earnings per share calculation	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossAttributableToOwnersOfParent
960	Number of shares:	Abstract			ifrs-full:NumberOfSharesIssuedAbstract
961	Number of ordinary shares for the purpose of basic earnings per share calculation	Concept (Shares)	For Period		ifrs-full:WeightedAverageShares
962	Effect of dilutive potential ordinary shares under the share option schemes	Concept (Shares)	For Period		ifrs-full:DilutiveEffectOfShareOptionsOnNumberOfOrdinaryShares
963	Weighted average number of ordinary shares for the purpose of diluted earnings per share	Concept (Shares)	For Period		ifrs-full:AdjustedWeightedAverageShares
964	Earnings per share:	Abstract			ifrs-full:BasicAndDilutedEarningsPerShareAbstract
965	Basic (RMB Yuan)	Concept (Share)	For Period		ifrs-full:BasicEarningsLossPerShare
966	Diluted (RMB Yuan)	Concept (Share)	For Period		ifrs-full:DilutedEarningsLossPerShare
967	41201 - Disclosure - DIVIDENDS (Details)	Network	*	*	http://www.cnoocltd.com/role/DividendsDetails
968	Implied Table	Table	*	*	implied:Table
969	DIVIDENDS [abstract]	Abstract			ceo:DividendsAbstract
970	Dividend per ordinary share:	Abstract			ceo:DividendPerOrdinaryShareAbstract
971	Interim dividend	Concept (Monetary)	For Period	Debit	ceo:InterimDividendsClassifiedAsFinancingActivities
972	Interim dividend per ordinary share	Concept (Share)	For Period		ceo:DividendsRecognisedAsDistributionsToOwnersOfParentRelatingToPriorYearsPerOrdinaryShare
973	Final dividend	Concept (Monetary)	For Period	Debit	ceo:FinalDividendsClassifiedAsFinancingActivities
974	Final dividend per ordinary share	Concept (Share)	For Period		ifrs-full:DividendsRecognisedAsDistributionsToOwnersPerShare
975	Final dividend proposed by the Board of Directors - not recognized as a liability as at the end of the year	Concept (Monetary)	For Period		ifrs-full:DividendsProposedOrDeclaredBeforeFinancialStatementsAuthorisedForIssueButNotRecognisedAsDistributionToOwners
976	Final dividend proposed per ordinary share by the Board of Directors - not recognized as a liability as at the end of the year	Concept (Share)	For Period		ifrs-full:DividendsProposedOrDeclaredBeforeFinancialStatementsAuthorisedForIssueButNotRecognisedAsDistributionToOwnersPerShare
977	Corporate income tax rate	Concept (Percent)	For Period		ceo:CorporateIncomeTaxRateResultingFromDistributionOfDividendsToNonresidentEnterpriseShareholders
978	41301 - Disclosure - PROPERTY, PLANT AND EQUIPMENT (Details)	Network	*	*	http://www.cnoocltd.com/role/PropertyPlantAndEquipmentDetails
979	Disclosure of detailed information about property, plant and equipment [table]	Table	*	*	ifrs-full:DisclosureOfPropertyPlantAndEquipmentTable
980	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
981	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
982	Oil and gas properties [member]	Member			ifrs-full:OilAndGasAssetsMember
983	Vehicles and office equipment and others [member]	Member			ceo:VehiclesAndOfficeEquipmentAndOtherPropertyPlantAndEquipmentMember
984	Carrying amount, accumulated depreciation, amortisation and impairment and gross carrying amount [axis]	Axis			ifrs-full:CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis
985	Net book value [member]	Member			ifrs-full:CarryingAmountMember
986	Cost [member]	Member			ifrs-full:GrossCarryingAmountMember
987	Accumulated depreciation, depletion and amortization and impairment [member]	Member			ifrs-full:AccumulatedDepreciationAmortisationAndImpairmentMember
988	Disclosure of detailed information about property, plant and equipment [line items]	LineItems			ifrs-full:DisclosureOfPropertyPlantAndEquipmentLineItems
989	Balance at beginning of period	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
990	Additions	Concept (Monetary)	For Period	Debit	ifrs-full:AdditionsOtherThanThroughBusinessCombinationsPropertyPlantAndEquipment
991	Acquisitions	Concept (Monetary)	For Period	Debit	ifrs-full:AcquisitionsThroughBusinessCombinationsPropertyPlantAndEquipment
992	Depreciation charge for the year	Concept (Monetary)	For Period		ifrs-full:DepreciationPropertyPlantAndEquipment
993	Impairment	Concept (Monetary)	For Period		ifrs-full:ImpairmentLossRecognisedInProfitOrLossPropertyPlantAndEquipment
994	Disposals and write-offs	Concept (Monetary)	For Period	Credit	ifrs-full:DisposalsAndRetirementsPropertyPlantAndEquipment
995	Exchange differences	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughNetExchangeDifferencesPropertyPlantAndEquipment
996	Balance at end of period	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
997	41302 - Disclosure - PROPERTY, PLANT AND EQUIPMENT - Narrative (Details)	Network	*	*	http://www.cnoocltd.com/role/PropertyPlantAndEquipmentNarrativeDetails
998	Disclosure of detailed information about property, plant and equipment [table]	Table	*	*	ifrs-full:DisclosureOfPropertyPlantAndEquipmentTable
999	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
1000	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
1001	Oil and gas properties [member]	Member			ifrs-full:OilAndGasAssetsMember
1002	Exploration and evaluation assets [member]	Member			ifrs-full:ExplorationAndEvaluationAssetsMember
1003	Types of projects [axis]	Axis			ceo:TypesOfProjectsAxis
1004	Types of projects [member]	Member			ceo:TypesOfProjectsMember
1005	Long Lake project [member]	Member			ceo:LongLakeProjectMember
1006	Range [axis]	Axis			ifrs-full:RangeAxis
1007	Ranges [member]	Member			ifrs-full:RangesMember
1008	Maximum [member]	Member			ifrs-full:TopOfRangeMember
1009	Minimum [member]	Member			ifrs-full:BottomOfRangeMember
1010	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
1011	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
1012	North America [member]	Member			srt:NorthAmericaMember
1013	Disclosure of detailed information about property, plant and equipment [line items]	LineItems			ifrs-full:DisclosureOfPropertyPlantAndEquipmentLineItems
1014	Additions in respect of interest capitalized in property, plant and equipment (note 7)	Concept (Monetary)	For Period		ifrs-full:BorrowingCostsCapitalised
1015	Depreciation charge for the year in respect of a depreciation charge on dismantlement cost capitalized in oil and gas properties	Concept (Monetary)	For Period	Debit	ceo:DepreciationChargeOnDismantlementCostCapitalized
1016	Exploration expenses	Concept (Monetary)	For Period	Debit	ifrs-full:ExpenseArisingFromExplorationForAndEvaluationOfMineralResources
1017	Discount rate for value in use calculations after tax	Concept (Percent)	As Of		ifrs-full:DescriptionOfDiscountRatesUsedInCurrentEstimateOfValueInUse
1018	Derived pre-tax discount rate	Concept (Percent)	As Of		ceo:DerivedPretaxDiscountRate
1019	Estimated recoverable amount	Concept (Monetary)	As Of	Debit	ifrs-full:RecoverableAmountOfAssetOrCashgeneratingUnit
1020	41401 - Disclosure - INTANGIBLE ASSETS (Details)	Network	*	*	http://www.cnoocltd.com/role/IntangibleAssetsDetails
1021	Disclosure of reconciliation of changes in intangible assets and goodwill [table]	Table	*	*	ifrs-full:DisclosureOfReconciliationOfChangesInIntangibleAssetsAndGoodwillTable
1022	Classes of intangible assets and goodwill [axis]	Axis			ifrs-full:ClassesOfIntangibleAssetsAndGoodwillAxis
1023	Intangible assets and goodwill [member]	Member			ifrs-full:IntangibleAssetsAndGoodwillMember
1024	Gas processing rights under NWS Project [member]	Member			ceo:GasProcessingRightsUnderNwsProjectMember
1025	Drilling rig contracts and seismic data usage rights [member]	Member			ceo:DrillingRigContractsAndSeismicDataUsageRightsMember
1026	Marketing transportation and storage contracts [member]	Member			ceo:MarketingTransportationAndStorageContractsMember
1027	Software and others [member]	Member			ceo:SoftwareAndOtherIntangibleAssetsMember
1028	Goodwill [member]	Member			ifrs-full:GoodwillMember
1029	Carrying amount, accumulated depreciation, amortisation and impairment and gross carrying amount [axis]	Axis			ifrs-full:CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis
1030	Net book value [member]	Member			ifrs-full:CarryingAmountMember
1031	Cost [member]	Member			ifrs-full:GrossCarryingAmountMember
1032	Accumulated amortization [member]	Member			ifrs-full:AccumulatedDepreciationAndAmortisationMember
1033	Range [axis]	Axis			ifrs-full:RangeAxis
1034	Ranges [member]	Member			ifrs-full:RangesMember
1035	Maximum [member]	Member			ifrs-full:TopOfRangeMember
1036	Minimum [member]	Member			ifrs-full:BottomOfRangeMember
1037	Disclosure of reconciliation of changes in intangible assets and goodwill [line items]	LineItems			ifrs-full:DisclosureOfReconciliationOfChangesInIntangibleAssetsAndGoodwillLineItems
1038	Balance at beginning of year	Concept (Monetary)	As Of	Debit	ifrs-full:IntangibleAssetsAndGoodwill
1039	Additions	Concept (Monetary)	For Period	Debit	ifrs-full:AdditionsOtherThanThroughBusinessCombinationsIntangibleAssetsOtherThanGoodwill
1040	Amortization charge for the year	Concept (Monetary)	For Period		ifrs-full:AmortisationIntangibleAssetsOtherThanGoodwill
1041	Disposal	Concept (Monetary)	For Period	Credit	ifrs-full:DisposalsIntangibleAssetsAndGoodwill
1042	Exchange differences	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughNetExchangeDifferencesIntangibleAssetsAndGoodwill
1043	Balance at end of year	Concept (Monetary)	As Of	Debit	ifrs-full:IntangibleAssetsAndGoodwill
1044	Straight-line amortization period, identifiable intangible assets	Concept (Text/String)	For Period		ifrs-full:UsefulLivesOrAmortisationRatesIntangibleAssetsOtherThanGoodwill
1045	41501 - Disclosure - INVESTMENTS IN ASSOCIATES - Particulars of principal associates (Details)	Network	*	*	http://www.cnoocltd.com/role/InvestmentsInAssociatesParticularsOfPrincipalAssociatesDetails
1046	Disclosure of associates [table]	Table	*	*	ifrs-full:DisclosureOfSignificantInvestmentsInAssociatesTable
1047	Associates [axis]	Axis			ifrs-full:SignificantInvestmentsInAssociatesAxis
1048	Entity's total for associates [member]	Member			ifrs-full:EntitysTotalForAssociatesMember
1049	Associates [member]	Member			ifrs-full:AssociatesMember
1050	Shanghai Petroleum Corporation Limited [member]	Member			ceo:ShanghaiPetroleumCorporationLimitedMember
1051	CNOOC Finance Corporation Limited [member]	Member			ceo:CnoocFinanceCorporationLimitedMember
1052	Disclosure of associates [line items]	LineItems			ifrs-full:DisclosureOfSignificantInvestmentsInAssociatesLineItems
1053	Name of associates	Concept (Text/String)	For Period		ifrs-full:NameOfAssociate
1054	Place of establishment	Concept (Text/String)	For Period		ifrs-full:PrincipalPlaceOfBusinessOfAssociate
1055	Nominal value of ordinary shares issued and paid-up/registered capital	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
1056	Percentage of equity attributable to the Group	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInAssociate
1057	Principal activities	Concept (Text/String)	For Period		ifrs-full:DescriptionOfNatureOfEntitysOperationsAndPrincipalActivities
1058	41502 - Disclosure - INVESTMENTS IN ASSOCIATES - The Group's investments in associates (Details)	Network	*	*	http://www.cnoocltd.com/role/InvestmentsInAssociatesTheGroupsInvestmentsInAssociatesDetails
1059	Disclosure of associates [table]	Table	*	*	ifrs-full:DisclosureOfSignificantInvestmentsInAssociatesTable
1060	Associates [axis]	Axis			ifrs-full:SignificantInvestmentsInAssociatesAxis
1061	Entity's total for associates [member]	Member			ifrs-full:EntitysTotalForAssociatesMember
1062	Associates [member]	Member			ifrs-full:AssociatesMember
1063	Disclosure of associates [line items]	LineItems			ifrs-full:DisclosureOfSignificantInvestmentsInAssociatesLineItems
1064	Share of net assets	Concept (Monetary)	As Of	Debit	ifrs-full:InvestmentsInAssociates
1065	41503 - Disclosure - INVESTMENTS IN ASSOCIATES - Summarized financial information of the Group's associates in the consolidated financial statements (Details)	Network	*	*	http://www.cnoocltd.com/role/InvestmentsInAssociatesSummarizedFinancialInformationOfTheGroupsAssociatesInTheConsolidatedFinancialStatementsDetails
1066	Disclosure of associates [table]	Table	*	*	ifrs-full:DisclosureOfSignificantInvestmentsInAssociatesTable
1067	Associates [axis]	Axis			ifrs-full:SignificantInvestmentsInAssociatesAxis
1068	Entity's total for associates [member]	Member			ifrs-full:EntitysTotalForAssociatesMember
1069	Associates [member]	Member			ifrs-full:AssociatesMember
1070	Disclosure of associates [line items]	LineItems			ifrs-full:DisclosureOfSignificantInvestmentsInAssociatesLineItems
1071	(Loss)/profit for the year	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfProfitLossOfAssociatesAccountedForUsingEquityMethod
1072	Other comprehensive (expense)/income	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfOtherComprehensiveIncomeOfAssociatesAndJointVenturesAccountedForUsingEquityMethodThatWillBeReclassifiedToProfitOrLossNetOfTax
1073	Total comprehensive (expense)/income	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfTotalComprehensiveIncomeOfAssociatesAndJointVenturesAccountedForUsingEquityMethod
1074	Dividend received from the associates	Concept (Monetary)	For Period	Debit	ifrs-full:DividendsReceivedFromAssociatesClassifiedAsInvestingActivities
1075	41601 - Disclosure - INVESTMENT IN A JOINT VENTURE - Particulars of the joint venture (Details)	Network	*	*	http://www.cnoocltd.com/role/InvestmentInAJointVentureParticularsOfTheJointVentureDetails
1076	Disclosure of joint ventures [table]	Table	*	*	ifrs-full:DisclosureOfJointVenturesTable
1077	Joint ventures [axis]	Axis			ifrs-full:JointVenturesAxis
1078	Entity's total for joint ventures [member]	Member			ifrs-full:EntitysTotalForJointVenturesMember
1079	Joint ventures [member]	Member			ifrs-full:JointVenturesMember
1080	BC ENERGY INVESTMENTS CORP. [member]	Member			ceo:BcEnergyInvestmentsCorporationMember
1081	Disclosure of joint ventures [line items]	LineItems			ifrs-full:DisclosureOfJointVenturesLineItems
1082	Name of entity	Concept (Text/String)	For Period		ifrs-full:NameOfJointVenture
1083	Place of establishment	Concept (Text/String)	For Period		ifrs-full:PrincipalPlaceOfBusinessOfJointVenture
1084	Nominal value of ordinary shares issued and paid-up/registered capital	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
1085	Percentage of equity attributable to the Group	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInJointVenture
1086	Principal activities	Concept (Text/String)	For Period		ifrs-full:DescriptionOfNatureOfEntitysOperationsAndPrincipalActivities
1087	41602 - Disclosure - INVESTMENT IN A JOINT VENTURE - Summarized financial information of the joint venture (Details)	Network	*	*	http://www.cnoocltd.com/role/InvestmentInAJointVentureSummarizedFinancialInformationOfTheJointVentureDetails
1088	Disclosure of joint ventures [table]	Table	*	*	ifrs-full:DisclosureOfJointVenturesTable
1089	Joint ventures [axis]	Axis			ifrs-full:JointVenturesAxis
1090	Entity's total for joint ventures [member]	Member			ifrs-full:EntitysTotalForJointVenturesMember
1091	Joint ventures [member]	Member			ifrs-full:JointVenturesMember
1092	Disclosure of joint ventures [line items]	LineItems			ifrs-full:DisclosureOfJointVenturesLineItems
1093	Current assets	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentAssets
1094	Non-current assets	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentAssets
1095	Current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentLiabilities
1096	Non-current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentLiabilities
1097	Revenue	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
1098	Depreciation, depletion and amortization	Concept (Monetary)	For Period	Debit	ifrs-full:DepreciationAndAmortisationExpense
1099	Interest income	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromInterest
1100	Finance costs	Concept (Monetary)	For Period	Debit	ifrs-full:FinanceCosts
1101	Profit/(loss) before tax	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossBeforeTax
1102	Income tax expense	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
1103	Profit/(loss) after tax	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
1104	Total comprehensive income/(expense)	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncome
1105	Dividends received from a joint venture	Concept (Monetary)	For Period	Debit	ifrs-full:DividendsReceivedFromJointVenturesClassifiedAsInvestingActivities
1106	41701 - Disclosure - EQUITY INVESTMENTS AND OTHER FINANCIAL ASSETS - Equity investments (Details)	Network	*	*	http://www.cnoocltd.com/role/EquityInvestmentsAndOtherFinancialAssetsEquityInvestmentsDetails
1107	Disclosure of financial assets [table]	Table	*	*	ifrs-full:DisclosureOfFinancialAssetsTable
1108	Categories of financial assets [axis]	Axis			ifrs-full:CategoriesOfFinancialAssetsAxis
1109	Financial assets, category [member]	Member			ifrs-full:FinancialAssetsCategoryMember
1110	Equity investments classified at FVTOCI [member]	Member			ifrs-full:InvestmentsInEquityInstrumentsMeasuredAtFairValueThroughOtherComprehensiveIncomeMember
1111	Equity investment classified at FVTPL [member]	Member			ifrs-full:FinancialAssetsAtFairValueThroughProfitOrLossCategoryMember
1112	Classes of financial assets [axis]	Axis			ifrs-full:ClassesOfFinancialAssetsAxis
1113	Financial assets, class [member]	Member			ifrs-full:FinancialAssetsMember
1114	Current: Non-publicly traded investments [member]	Member			ceo:CurrentNonpubliclyTradedInvestmentsMember
1115	Non-current: Publicly traded investments [member]	Member			ceo:NoncurrentPubliclyTradedInvestmentsMember
1116	Non-current: Non-publicly traded investments [member]	Member			ceo:NoncurrentNonpubliclyTradedInvestmentsMember
1117	Counterparties [axis]	Axis			ifrs-full:CounterpartiesAxis
1118	Counterparties [member]	Member			ifrs-full:CounterpartiesMember
1119	MEG Energy Corporation ("MEG") [member]	Member			ceo:MegEnergyCorporationMember
1120	Kerogen Energy Fund [member]	Member			ceo:KerogenEnergyFundMember
1121	GEMS O&G II Fund [member]	Member			ceo:GemsOGIIFundMember
1122	Disclosure of financial assets [line items]	LineItems			ifrs-full:DisclosureOfFinancialAssetsLineItems
1123	Equity investments	Abstract			ceo:DisclosureOfDetailedInformationAboutEquityInvestmentsAbstract
1124	Current equity investments	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentInvestmentsInEquityInstrumentsDesignatedAtFairValueThroughOtherComprehensiveIncome
1125	Non-current equity investments classified at FVTOCI	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentInvestmentsInEquityInstrumentsDesignatedAtFairValueThroughOtherComprehensiveIncome
1126	Other equity investments classified at FVTPL	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentFinancialAssetsAtFairValueThroughProfitOrLoss
1127	Non-current equity investments	Concept (Monetary)	As Of	Debit	ceo:NoncurrentInvestmentsInEquityInstruments
1128	Cumulative loss on disposal of GEMS O&G II fund	Concept (Monetary)	For Period	Credit	ifrs-full:CumulativeGainLossOnDisposalOfInvestmentsInEquityInstrumentsDesignatedAsMeasuredAtFairValueThroughOtherComprehensiveIncome
1129	Consideraton	Concept (Monetary)	As Of	Credit	ceo:ConsiderationPaidReceivedOfOtherEquityInvestmentClassifiedAtFairValueThroughProfitLoss
1130	Gain on disposal recognized in the profit or loss	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitsLossesOnDisposalOfInvestmentsAndChangesInValueOfInvestments
1131	41702 - Disclosure - EQUITY INVESTMENTS AND OTHER FINANCIAL ASSETS - Other financial assets (Details)	Network	*	*	http://www.cnoocltd.com/role/EquityInvestmentsAndOtherFinancialAssetsOtherFinancialAssetsDetails
1132	Disclosure of financial assets [table]	Table	*	*	ifrs-full:DisclosureOfFinancialAssetsTable
1133	Categories of financial assets [axis]	Axis			ifrs-full:CategoriesOfFinancialAssetsAxis
1134	Financial assets, category [member]	Member			ifrs-full:FinancialAssetsCategoryMember
1135	Other financial assets classified at FVTPL [member]	Member			ifrs-full:FinancialAssetsAtFairValueThroughProfitOrLossCategoryMember
1136	Classes of financial assets [axis]	Axis			ifrs-full:ClassesOfFinancialAssetsAxis
1137	Financial assets, class [member]	Member			ifrs-full:FinancialAssetsMember
1138	Corporate wealth management products [member]	Member			ceo:CorporateWealthManagementProductsClassifiedAsOtherCurrentFinancialAssetsMember
1139	Money market funds [member]	Member			ceo:MoneyMarketFundsMember
1140	Disclosure of financial assets [line items]	LineItems			ifrs-full:DisclosureOfFinancialAssetsLineItems
1141	Other financial assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherCurrentFinancialAssets
1142	41703 - Disclosure - EQUITY INVESTMENTS AND OTHER FINANCIAL ASSETS - Narrative (Details)	Network	*	*	http://www.cnoocltd.com/role/EquityInvestmentsAndOtherFinancialAssetsNarrativeDetails
1143	Disclosure of financial assets [table]	Table	*	*	ifrs-full:DisclosureOfFinancialAssetsTable
1144	Categories of financial assets [axis]	Axis			ifrs-full:CategoriesOfFinancialAssetsAxis
1145	Financial assets, category [member]	Member			ifrs-full:FinancialAssetsCategoryMember
1146	Other financial assets [member]	Member			ceo:OtherFinancialAssetsMember
1147	Equity investments [member]	Member			ifrs-full:EquityInvestmentsMember
1148	Disclosure of financial assets [line items]	LineItems			ifrs-full:DisclosureOfFinancialAssetsLineItems
1149	The gains of ther Group's other financial assets recognized in the profit or loss for the year	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnFinancialAssetsAtFairValueThroughProfitOrLoss
1150	The fair value changes on the Group's investment recognized directly in other comprehensive expense	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeNetOfTaxGainsLossesFromInvestmentsInEquityInstruments
1151	41801 - Disclosure - OTHER NON-CURRENT ASSETS (Details)	Network	*	*	http://www.cnoocltd.com/role/OtherNoncurrentAssetsDetails
1152	Implied Table	Table	*	*	implied:Table
1153	OTHER NON-CURRENT ASSETS [abstract]	Abstract			ifrs-full:MiscellaneousNoncurrentAssetsAbstract
1154	Specified dismantlement fund accounts	Concept (Monetary)	As Of	Debit	ceo:SpecifiedDismantlementFund
1155	41901 - Disclosure - INVENTORIES AND SUPPLIES (Details)	Network	*	*	http://www.cnoocltd.com/role/InventoriesAndSuppliesDetails
1156	Implied Table	Table	*	*	implied:Table
1157	INVENTORIES AND SUPPLIES [abstract]	Abstract			ifrs-full:ClassesOfInventoriesAbstract
1158	Materials and supplies	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentRawMaterialsAndCurrentProductionSupplies
1159	Oil in tanks	Concept (Monetary)	As Of	Debit	ifrs-full:FinishedGoods
1160	Less: Provision for inventory obsolescence	Concept (Monetary)	As Of	Credit	ceo:ProvisionForInventoryObsolescence
1161	Total inventories and supplies	Concept (Monetary)	As Of	Debit	ifrs-full:Inventories
1162	42001 - Disclosure - TRADE RECEIVABLES (Details)	Network	*	*	http://www.cnoocltd.com/role/TradeReceivablesDetails
1163	Disclosure of detailed information about trade receivables [table]	Table	*	*	ceo:DisclosureOfDetailedInformationAboutTradeReceivablesTable
1164	Range [axis]	Axis			ifrs-full:RangeAxis
1165	Ranges [member]	Member			ifrs-full:RangesMember
1166	Maximum [member]	Member			ifrs-full:TopOfRangeMember
1167	Disclosure of detailed information about trade receivables [line items]	LineItems			ceo:DisclosureOfDetailedInformationAboutTradeReceivablesLineItems
1168	Credit terms	Concept (xbrli:durationItemType)	For Period		ceo:CreditTermsOfTradeReceivablesAfterDeliveryOfOilAndGas
1169	Age of trade receivables	Concept (xbrli:durationItemType)	For Period		ceo:AgeOfTradeReceivables
1170	42101 - Disclosure - CASH AND CASH EQUIVALENTS AND TIME DEPOSITS WITH MATURITY OVER THREE MONTHS (Details)	Network	*	*	http://www.cnoocltd.com/role/CashAndCashEquivalentsAndTimeDepositsWithMaturityOverThreeMonthsDetails
1171	Disclosure of detailed information about cash and cash equivalents and time deposits with maturity over three months [table]	Table	*	*	ceo:DisclosureOfDetailedInformationAboutCashAndCashEquivalentsAndTimeDepositsWithMaturityOverThreeMonthsTable
1172	Range [axis]	Axis			ifrs-full:RangeAxis
1173	Ranges [member]	Member			ifrs-full:RangesMember
1174	Maximum [member]	Member			ifrs-full:TopOfRangeMember
1175	Disclosure of detailed information about cash and cash equivalents and time deposits with maturity over three months [line items]	LineItems			ceo:DisclosureOfDetailedInformationAboutCashAndCashEquivalentsAndTimeDepositsWithMaturityOverThreeMonthsLineItems
1176	Maturity of current deposits and time deposits	Concept (xbrli:durationItemType)	For Period		ceo:MaturityOfCurrentDepositsAndTimeDeposits
1177	Weighted average effective interest rates of the Group's bank deposits	Concept (Percent)	As Of		ceo:WeightedAverageEffectiveInterestRatesOfBankDeposits
1178	42201 - Disclosure - TRADE AND ACCRUED PAYABLES (Details)	Network	*	*	http://www.cnoocltd.com/role/TradeAndAccruedPayablesDetails
1179	Disclosure of detailed information about trade and accrued payables [table]	Table	*	*	ceo:DisclosureOfDetailedInformationAboutTradeAndAccruedPayablesTable
1180	Range [axis]	Axis			ifrs-full:RangeAxis
1181	Ranges [member]	Member			ifrs-full:RangesMember
1182	Maximum [member]	Member			ifrs-full:TopOfRangeMember
1183	Disclosure of detailed information about trade and accrued payables [line items]	LineItems			ceo:DisclosureOfDetailedInformationAboutTradeAndAccruedPayablesLineItems
1184	Age of trade and accrued payables	Concept (Text/String)	For Period		ceo:AgeOfTradeAndAccruedPayables
1185	42301 - Disclosure - CONTRACT LIABILITIES (Details)	Network	*	*	http://www.cnoocltd.com/role/ContractLiabilitiesDetails
1186	Implied Table	Table	*	*	implied:Table
1187	CONTRACT LIABILITIES [abstract]	Abstract			ifrs-full:ContractLiabilitiesAbstract
1188	At January 1	Concept (Monetary)	As Of	Credit	ifrs-full:ContractLiabilities
1189	Recognized revenue in current period	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromContractsWithCustomers
1190	At December 31	Concept (Monetary)	As Of	Credit	ifrs-full:ContractLiabilities
1191	-Current	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentContractLiabilities
1192	42401 - Disclosure - OTHER PAYABLES AND ACCRUED LIABILITIES (Details)	Network	*	*	http://www.cnoocltd.com/role/OtherPayablesAndAccruedLiabilitiesDetails
1193	Implied Table	Table	*	*	implied:Table
1194	OTHER PAYABLES AND ACCRUED LIABILITIES [abstract]	Abstract			ceo:OtherPayablesAndAccruedLiabilitiesAbstract
1195	Accrued payroll and welfare payable	Concept (Monetary)	As Of	Credit	ceo:AccruedPayrollAndWelfarePayable
1196	Accruals expenses	Concept (Monetary)	As Of	Credit	ifrs-full:Accruals
1197	Advances from customers	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentAdvances
1198	Special oil gain levy payable	Concept (Monetary)	As Of	Credit	ceo:SpecialOilGainLevyPayable
1199	Royalties payable	Concept (Monetary)	As Of	Credit	ceo:RoyaltiesPayable
1200	Provision for dismantlement (note 26)	Concept (Monetary)	As Of	Credit	ceo:CurrentPortionForDismantlementClassifiedAsOtherPayablesAndAccruedLiabilities
1201	Other payables	Concept (Monetary)	As Of	Credit	ifrs-full:OtherPayables
1202	Other payables and accrued liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentAccruedExpensesAndOtherCurrentLiabilities
1203	42501 - Disclosure - LOANS AND BORROWINGS - Current (Details)	Network	*	*	http://www.cnoocltd.com/role/LoansAndBorrowingsCurrentDetails
1204	Disclosure of current loans and borrowings [table]	Table	*	*	ceo:DisclosureOfCurrentLoansAndBorrowingsTable
1205	Liabilities arising from financing activities [axis]	Axis			ifrs-full:LiabilitiesArisingFromFinancingActivitiesAxis
1206	Liabilities arising from financing activities [member]	Member			ifrs-full:LiabilitiesArisingFromFinancingActivitiesMember
1207	Short-term loans and borrowings [member]	Member			ifrs-full:ShorttermBorrowingsMember
1208	General loans [member]	Member			ceo:GeneralLoansMember
1209	Loans and borrowings due within one year [member]	Member			ceo:LoansAndBorrowingsDueWithinOneYearMember
1210	For Tangguh LNG Project [member]	Member			ceo:TangguhLngProjectMember
1211	Notes [member]	Member			ceo:NotesFullyAndUnconditionallyGuaranteedByCompanyMember
1212	Range [axis]	Axis			ifrs-full:RangeAxis
1213	Ranges [member]	Member			ifrs-full:RangesMember
1214	Minimum [member]	Member			ifrs-full:BottomOfRangeMember
1215	Maximum [member]	Member			ifrs-full:TopOfRangeMember
1216	Disclosure of current loans and borrowings [line items]	LineItems			ceo:DisclosureOfCurrentLoansAndBorrowingsLineItems
1217	Effective interest rate basis	Concept (Text/String)	For Period		ifrs-full:BorrowingsInterestRateBasis
1218	Effective interest rate, adjustment to LIBOR	Concept (Percent)	As Of		ifrs-full:BorrowingsAdjustmentToInterestRateBasis
1219	Final maturity	Concept (Text/String)	For Period		ifrs-full:BorrowingsMaturity
1220	Loans	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentLoansReceivedAndCurrentPortionOfNoncurrentLoansReceived
1221	Notes	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentNotesAndDebenturesIssuedAndCurrentPortionOfNoncurrentNotesAndDebenturesIssued
1222	Total	Concept (Monetary)	As Of	Credit	ifrs-full:ShorttermBorrowings
1223	42502 - Disclosure - LOANS AND BORROWINGS - Non-current (Details)	Network	*	*	http://www.cnoocltd.com/role/LoansAndBorrowingsNoncurrent
1224	Disclosure of non-current loans and borrowings [table]	Table	*	*	ceo:DisclosureOfNoncurrentLoansAndBorrowingsTable
1225	Liabilities arising from financing activities [axis]	Axis			ifrs-full:LiabilitiesArisingFromFinancingActivitiesAxis
1226	Liabilities arising from financing activities [member]	Member			ifrs-full:LiabilitiesArisingFromFinancingActivitiesMember
1227	Long-term loans and borrowings [member]	Member			ifrs-full:LongtermBorrowingsMember
1228	For Tangguh LNG Project [member]	Member			ceo:TangguhLngProjectMember
1229	For Tangguh LNG III Project [member]	Member			ceo:ThirdLngProcessTrainOfTangguhLngProjectMember
1230	Notes [member]	Member			ceo:NotesFullyAndUnconditionallyGuaranteedByCompanyMember
1231	Range [axis]	Axis			ifrs-full:RangeAxis
1232	Ranges [member]	Member			ifrs-full:RangesMember
1233	Minimum [member]	Member			ifrs-full:BottomOfRangeMember
1234	Maximum [member]	Member			ifrs-full:TopOfRangeMember
1235	Disclosure of non-current loans and borrowings [line items]	LineItems			ceo:DisclosureOfNoncurrentLoansAndBorrowingsLineItems
1236	Effective interest rate basis	Concept (Text/String)	For Period		ifrs-full:BorrowingsInterestRateBasis
1237	Effective interest rate, adjustment to LIBOR	Concept (Percent)	As Of		ifrs-full:BorrowingsAdjustmentToInterestRateBasis
1238	Final maturity	Concept (Text/String)	For Period		ceo:MaturityOfNoncurrentLoansAndBorrowings
1239	Loans	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentPortionOfNoncurrentLoansReceived
1240	Notes	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentPortionOfNoncurrentNotesAndDebenturesIssued
1241	Total	Concept (Monetary)	As Of	Credit	ifrs-full:LongtermBorrowings
1242	42503 - Disclosure - LOANS AND BORROWINGS - Details of notes (Details)	Network	*	*	http://www.cnoocltd.com/role/LoansAndBorrowingsDetailsOfNotesDetails
1243	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
1244	Issued By Company [axis]	Axis			ceo:IssuedByCompanyAxis
1245	Issued By Company [member]	Member			ceo:IssuedByCompanyMember
1246	CNOOC Finance (2003) Limited (Note One) [member]	Member			ceo:CnoocFinance2003LimitedNoteOneMember
1247	CNOOC Finance (2011) Limited (Note One) [member]	Member			ceo:CnoocFinance2011LimitedNoteOneMember
1248	CNOOC Finance (2011) Limited (Note Two) [member]	Member			ceo:CnoocFinance2011LimitedNoteTwoMember
1249	CNOOC Finance (2012) Limited (Note One) [member]	Member			ceo:CnoocFinance2012LimitedNoteOneMember
1250	CNOOC Finance (2012) Limited (Note Two) [member]	Member			ceo:CnoocFinance2012LimitedNoteTwoMember
1251	CNOOC Finance (2013) Limited (Note One) [member]	Member			ceo:CnoocFinance2013LimitedNoteOneMember
1252	CNOOC Finance (2013) Limited (Note Two) [member]	Member			ceo:CnoocFinance2013LimitedNoteTwoMember
1253	CNOOC Finance (2013) Limited (Note Three) [member]	Member			ceo:CnoocFinance2013LimitedNoteThreeMember
1254	CNOOC Nexen Finance (2014) ULC (Note One) [member]	Member			ceo:CnoocNexenFinance2014UlcNoteOneMember
1255	CNOOC Nexen Finance (2014) ULC (Note Two) [member]	Member			ceo:CnoocNexenFinance2014UlcNoteTwoMember
1256	CNOOC Petroleum North America ULC (Note One) [member]	Member			ceo:CnoocPetroleumNorthAmericaUlcNoteOneMember
1257	CNOOC Petroleum North America ULC (Note Two) [member]	Member			ceo:CnoocPetroleumNorthAmericaUlcNoteTwoMember
1258	CNOOC Petroleum North America ULC (Note Three) [member]	Member			ceo:CnoocPetroleumNorthAmericaUlcNoteThreeMember
1259	CNOOC Petroleum North America ULC (Note Four) [member]	Member			ceo:CnoocPetroleumNorthAmericaUlcNoteFourMember
1260	CNOOC Petroleum North America ULC (Note Five) [member]	Member			ceo:CnoocPetroleumNorthAmericaUlcNoteFiveMember
1261	CNOOC Petroleum North America ULC (Note Six) [member]	Member			ceo:CnoocPetroleumNorthAmericaUlcNoteSixMember
1262	CNOOC Finance (2015) U.S.A. LLC (Note One) [member]	Member			ceo:CnoocFinance2015USALlcNoteOneMember
1263	CNOOC Finance (2015) Australia Pty Ltd (Note One) [member]	Member			ceo:CnoocFinance2015AustraliaPtyLtdNoteOneMember
1264	CNOOC Finance (2015) Australia Pty Ltd (Note Two) [member]	Member			ceo:CnoocFinance2015AustraliaPtyLtdNoteTwoMember
1265	CNOOC Finance (2015) U.S.A. LLC (Note Two) [member]	Member			ceo:CnoocFinance2015USALlcNoteTwoMember
1266	CNOOC Finance (2015) U.S.A. LLC (Note Three) [member]	Member			ceo:CnoocFinance2015USALlcNoteThreeMember
1267	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
1268	Issued by	Concept (Text/String)	For Period		ceo:NotesOfLoansAndBorrowingsIssuedByEntities
1269	Maturity	Concept (Text/String)	For Period		ifrs-full:BorrowingsMaturity
1270	Coupon Rate	Concept (Percent)	As Of		ifrs-full:BorrowingsInterestRate
1271	Outstanding Principal Amount	Concept (Monetary)	As Of		ifrs-full:NotionalAmount
1272	42504 - Disclosure - LOANS AND BORROWINGS - Narrative (Details)	Network	*	*	http://www.cnoocltd.com/role/LoansAndBorrowingsNarrativeDetails
1273	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
1274	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
1275	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
1276	General loans [member]	Member			ceo:GeneralLoansMember
1277	Tangguh LNG Project [member]	Member			ceo:TangguhLngProjectMember
1278	Third LNG process train of Tangguh LNG Project [member]	Member			ceo:ThirdLngProcessTrainOfTangguhLngProjectMember
1279	Categories of related parties [axis]	Axis			ifrs-full:CategoriesOfRelatedPartiesAxis
1280	Entity's total for related parties [member]	Member			ifrs-full:EntitysTotalForRelatedPartiesMember
1281	Mizuho Corporate Bank, Ltd. [member]	Member			ceo:MizuhoCorporateBankLtdMember
1282	Range [axis]	Axis			ifrs-full:RangeAxis
1283	Ranges [member]	Member			ifrs-full:RangesMember
1284	Maximum [member]	Member			ifrs-full:TopOfRangeMember
1285	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
1286	Aggregate loan amount under commercial loan agreements	Concept (Monetary)	As Of	Credit	ceo:AggregateLoanAmountUnderCommercialLoanAgreements
1287	Aggregate maximum cap under the subject loan agreement	Concept (Monetary)	As Of	Credit	ceo:PaymentObligationsGuaranteedByEntityOfTrusteeBorrowerUnderCommercialLoanAgreements
1288	Number of commercial loan agreements	Concept (Integer)	As Of		ceo:NumberOfCommercialLoanAgreements
1289	Bank loans guaranteed by the Company	Concept (Monetary)	As Of	Credit	ifrs-full:SecuredBankLoansReceived
1290	Shareholder loans of the Group	Concept (Monetary)	As Of	Credit	ceo:ShareholderLoansReceived
1291	42505 - Disclosure - LOANS AND BORROWINGS - Maturities of long term bank loans (Details)	Network	*	*	http://www.cnoocltd.com/role/LoansAndBorrowingsMaturitiesOfLongTermBankLoansDetails
1292	Disclosure of detailed information about long term bank loans [table]	Table	*	*	ceo:DisclosureOfDetailedInformationAboutLongTermBankLoansTable
1293	Maturity [axis]	Axis			ifrs-full:MaturityAxis
1294	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
1295	Within one year [member]	Member			ifrs-full:NotLaterThanOneYearMember
1296	After one year but within two years [member]	Member			ifrs-full:LaterThanOneYearAndNotLaterThanTwoYearsMember
1297	After two years but within three years [member]	Member			ifrs-full:LaterThanTwoYearsAndNotLaterThanThreeYearsMember
1298	After three years but within four years [member]	Member			ifrs-full:LaterThanThreeYearsAndNotLaterThanFourYearsMember
1299	After four years but within five years [member]	Member			ifrs-full:LaterThanFourYearsAndNotLaterThanFiveYearsMember
1300	After five years [member]	Member			ifrs-full:LaterThanFiveYearsMember
1301	Disclosure of detailed information about long term bank loans [line items]	LineItems			ceo:DisclosureOfDetailedInformationAboutLongTermBankLoansLineItems
1302	Repayable:	Abstract			ceo:RepayableMaturitiesOfLongTermBankLoansAbstract
1303	Total long term bank loans	Concept (Monetary)	As Of	Credit	ifrs-full:LoansReceived
1304	Amount due within one year shown under current liabilities	Concept (Monetary)	As Of	Credit	ceo:CurrentBankLoansReceivedAndCurrentPortionOfNoncurrentBankLoansReceived
1305	Long term bank loans repayable after one year	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentPortionOfNoncurrentLoansReceived
1306	42506 - Disclosure - LOANS AND BORROWINGS - Supplemental information with respect to long term bank loans (Details)	Network	*	*	http://www.cnoocltd.com/role/LoansAndBorrowingsSupplementalInformationWithRespectToLongTermBankLoansDetails
1307	Disclosure of detailed information about long term bank loans [table]	Table	*	*	ceo:DisclosureOfDetailedInformationAboutLongTermBankLoansTable
1308	Range [axis]	Axis			ifrs-full:RangeAxis
1309	Ranges [member]	Member			ifrs-full:RangesMember
1310	Weighted average [member]	Member			ifrs-full:WeightedAverageMember
1311	Maximum [member]	Member			ifrs-full:TopOfRangeMember
1312	Disclosure of detailed information about long term bank loans [line items]	LineItems			ceo:DisclosureOfDetailedInformationAboutLongTermBankLoansLineItems
1313	Total long term bank loans	Concept (Monetary)	As Of	Credit	ifrs-full:LoansReceived
1314	Interest rate	Concept (Percent)	As Of		ifrs-full:BorrowingsInterestRate
1315	Default of principal, interest or redemption terms of loans and borrowings	Concept (Monetary)	For Period	Credit	ceo:DefaultOfPrincipalInterestRedemptionTermsOfLoansAndBorrowings
1316	42601 - Disclosure - PROVISION FOR DISMANTLEMENT (Details)	Network	*	*	http://www.cnoocltd.com/role/ProvisionForDismantlementDetails
1317	Disclosure of other provisions [table]	Table	*	*	ifrs-full:DisclosureOfOtherProvisionsTable
1318	Classes of other provisions [axis]	Axis			ifrs-full:ClassesOfProvisionsAxis
1319	Other provisions [member]	Member			ifrs-full:OtherProvisionsMember
1320	Provision for dismantlement [member]	Member			ifrs-full:ProvisionForDecommissioningRestorationAndRehabilitationCostsMember
1321	Range [axis]	Axis			ifrs-full:RangeAxis
1322	Ranges [member]	Member			ifrs-full:RangesMember
1323	Minimum [member]	Member			ifrs-full:BottomOfRangeMember
1324	Maximum [member]	Member			ifrs-full:TopOfRangeMember
1325	Disclosure of other provisions [line items]	LineItems			ifrs-full:DisclosureOfOtherProvisionsLineItems
1326	At January 1	Concept (Monetary)	As Of	Credit	ifrs-full:OtherProvisions
1327	New projects	Concept (Monetary)	For Period	Credit	ifrs-full:NewProvisionsOtherProvisions
1328	Revision	Concept (Monetary)	For Period	Debit	ceo:ProvisionsRevisedOtherProvisions
1329	Utilization	Concept (Monetary)	For Period	Debit	ifrs-full:ProvisionUsedOtherProvisions
1330	Unwinding of discount (note 7)	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughTimeValueOfMoneyAdjustmentOtherProvisions
1331	Exchange differences	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughNetExchangeDifferencesOtherProvisions
1332	At December 31	Concept (Monetary)	As Of	Credit	ifrs-full:OtherProvisions
1333	Current portion of provision for dismantlement included in other payables and accrued liabilities (note 24)	Concept (Monetary)	As Of	Credit	ifrs-full:OtherShorttermProvisions
1334	At December 31, provision for dismantlement	Concept (Monetary)	As Of	Credit	ifrs-full:OtherLongtermProvisions
1335	Discount rate used for calculating provision for dismantlement	Concept (Percent)	As Of		ceo:DiscountRateUsedForCalculatingProvisionForDismantlement
1336	42701 - Disclosure - SHARE CAPITAL - Issued share capital (Details)	Network	*	*	http://www.cnoocltd.com/role/ShareCapitalIssuedShareCapitalDetails
1337	Implied Table	Table	*	*	implied:Table
1338	SHARE CAPITAL [abstract]	Abstract			ifrs-full:DisclosureOfClassesOfShareCapitalAbstract
1339	Number of shares	Concept (Shares)	As Of		ifrs-full:NumberOfSharesIssued
1340	Issued share capital equivalent of	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
1341	Par value	Concept (Share)	As Of		ifrs-full:ParValuePerShare
1342	42702 - Disclosure - SHARE CAPITAL - Share option schemes - Narrative (Details)	Network	*	*	http://www.cnoocltd.com/role/ShareCapitalShareOptionSchemes
1343	Disclosure of terms and conditions of share-based payment arrangement [table]	Table	*	*	ifrs-full:DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementTable
1344	Types of share-based payment arrangements [axis]	Axis			ifrs-full:TypesOfSharebasedPaymentArrangementsAxis
1345	Share-based payment arrangements [member]	Member			ifrs-full:SharebasedPaymentArrangementsMember
1346	2005 Share Option Scheme [member]	Member			ceo:ShareOptionScheme2005Member
1347	Range [axis]	Axis			ifrs-full:RangeAxis
1348	Ranges [member]	Member			ifrs-full:RangesMember
1349	Maximum [member]	Member			ifrs-full:TopOfRangeMember
1350	Disclosure of terms and conditions of share-based payment arrangement [line items]	LineItems			ifrs-full:DisclosureOfTermsAndConditionsOfSharebasedPaymentArrangementLineItems
1351	Ratio of number of shares issued upon exercise of options granted to total issued capital	Concept (Percent)	As Of		ceo:RatioOfNumberOfSharesIssuedUponExerciseOfOptionsGrantedToTotalIssuedCapital
1352	Consideration payable by a grantee for the grant of options	Concept (Share)	As Of		ceo:ConsiderationPayableByGranteesForGrantOfOptions
1353	Number of trading days preceding date of grant to determine average closing price of shares	Concept (xbrli:durationItemType)	For Period		ceo:NumberOfTradingDaysPrecedingDateOfGrantToDetermineAverageClosingPriceOfShares
1354	Exercise periods for the options granted from the date of grant	Concept (Decimal)	For Period		ifrs-full:DescriptionOfOptionLifeShareOptionsGranted
1355	New share option granted	Concept (Decimal)	For Period		ifrs-full:NumberOfInstrumentsOtherEquityInstrumentsGranted
1356	Equity-settled share option expense	Concept (Monetary)	For Period	Debit	ceo:EquitySettledShareOptionExpense
1357	42703 - Disclosure - SHARE CAPITAL - Details of share option schemes (Details)	Network	*	*	http://www.cnoocltd.com/role/ShareCapitalDetailsOfShareOptionSchemesDetails
1358	Implied Table	Table	*	*	implied:Table
1359	SHARE CAPITAL [abstract]	Abstract			ifrs-full:DisclosureOfClassesOfShareCapitalAbstract
1360	Number of share options outstanding at the beginning of the year	Concept (Decimal)	As Of		ifrs-full:NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement
1361	Number of share options granted during the year	Concept (Decimal)	For Period		ifrs-full:NumberOfInstrumentsOtherEquityInstrumentsGranted
1362	Number of share options forfeited during the year	Concept (Decimal)	For Period		ifrs-full:NumberOfOtherEquityInstrumentsForfeitedInSharebasedPaymentArrangement
1363	Number of share options expired during the year	Concept (Decimal)	For Period		ifrs-full:NumberOfOtherEquityInstrumentsExpiredInSharebasedPaymentArrangement
1364	Number of share options exercised during the year	Concept (Decimal)	For Period		ifrs-full:NumberOfOtherEquityInstrumentsExercisedOrVestedInSharebasedPaymentArrangement
1365	Number of share options outstanding at the end of the year	Concept (Decimal)	As Of		ifrs-full:NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement
1366	Number of share options exercisable at the end of the year	Concept (Decimal)	As Of		ifrs-full:NumberOfOtherEquityInstrumentsExercisableInSharebasedPaymentArrangement
1367	Weighted average exercise price outstanding at the beginning of the year	Concept (Monetary)	As Of		ifrs-full:WeightedAverageExercisePriceOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement
1368	Weighted average exercise price granted during the year	Concept (Monetary)	For Period		ifrs-full:WeightedAverageExercisePriceOfOtherEquityInstrumentsGrantedInSharebasedPaymentArrangement
1369	Weighted average exercise price forfeited during the year	Concept (Monetary)	For Period		ifrs-full:WeightedAverageExercisePriceOfOtherEquityInstrumentsForfeitedInSharebasedPaymentArrangement
1370	Weighted average exercise price expired during the year	Concept (Monetary)	For Period		ifrs-full:WeightedAverageExercisePriceOfOtherEquityInstrumentsExpiredInSharebasedPaymentArrangement
1371	Weighted average exercise price exercised during the year	Concept (Monetary)	For Period		ifrs-full:WeightedAverageExercisePriceOfOtherEquityInstrumentsExercisedOrVestedInSharebasedPaymentArrangement
1372	Weighted average exercise price outstanding at the end of the year	Concept (Monetary)	As Of		ifrs-full:WeightedAverageExercisePriceOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement
1373	Weighted average exercise price exercisable at the end of the year	Concept (Monetary)	As Of		ifrs-full:WeightedAverageExercisePriceOfOtherEquityInstrumentsExercisableInSharebasedPaymentArrangement
1374	Share options cancelled or modified during the year	Concept (Monetary)	For Period	Debit	ceo:ShareOptionsCancelledOrModifiedInSharebasedPaymentTransactions
1375	Ratio of the share options outstanding under share option schemes to the Company's shares in issue at the date of approval of consolidated financial statements for issuance	Concept (Percent)	As Of		ceo:RatioOfNumberOfSharesIssuedUponExerciseOfOptionsGrantedToTotalIssuedCapital
1376	Weighted average remaining contractual life of share options outstanding at the end of the year	Concept (Decimal)	As Of		ifrs-full:WeightedAverageRemainingContractualLifeOfOutstandingShareOptions
1377	Additional ordinary shares	Concept (Shares)	For Period		ifrs-full:IncreaseDecreaseInNumberOfOrdinarySharesIssued
1378	Additional share capital	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughSharebasedPaymentTransactions
1379	42801 - Disclosure - RESERVES (Details)	Network	*	*	http://www.cnoocltd.com/role/ReservesDetails
1380	Statement of changes in equity [table]	Table	*	*	ifrs-full:StatementOfChangesInEquityTable
1381	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
1382	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
1383	CNOOC China Limited [member]	Member			ceo:CnoocChinaLimitedMember
1384	Statement of changes in equity [line items]	LineItems			ifrs-full:StatementOfChangesInEquityLineItems
1385	General reserve fund	Concept (Monetary)	As Of	Credit	ifrs-full:StatutoryReserve
1386	Safety fund reserve	Concept (Monetary)	As Of	Credit	ceo:SafetyFundReserve
1387	42901 - Disclosure - RELATED PARTY TRANSACTIONS - Narrative (Details)	Network	*	*	http://www.cnoocltd.com/role/RelatedPartyTransactionsNarrativeDetails
1388	Disclosure of transactions between related parties [table]	Table	*	*	ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesTable
1389	Types of agreements in respect of related party transactions [axis]	Axis			ceo:TypesOfAgreementsInRespectOfRelatedPartyTransactionsAxis
1390	Types of agreements in respect of related party transactions [member]	Member			ceo:TypesOfAgreementsInRespectOfRelatedPartyTransactionsMember
1391	Comprehensive framework agreement [member]	Member			ceo:ComprehensiveFrameworkAgreementMember
1392	Categories of related parties [axis]	Axis			ifrs-full:CategoriesOfRelatedPartiesAxis
1393	Entity's total for related parties [member]	Member			ifrs-full:EntitysTotalForRelatedPartiesMember
1394	CNOOC Group [member]	Member			ceo:ChinaNationalOffshoreOilCorporationGroupMember
1395	Disclosure of transactions between related parties [line items]	LineItems			ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesLineItems
1396	Term of agreements	Concept (xbrli:durationItemType)	For Period		ceo:TermOfAgreements
1397	42902 - Disclosure - RELATED PARTY TRANSACTIONS - A summary of significant related party transactions (Details)	Network	*	*	http://www.cnoocltd.com/role/RelatedPartyTransactionsASummaryOfSignificantRelatedPartyTransactionsDetails
1398	Disclosure of transactions between related parties [table]	Table	*	*	ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesTable
1399	Types of agreements in respect of related party transactions [axis]	Axis			ceo:TypesOfAgreementsInRespectOfRelatedPartyTransactionsAxis
1400	Types of agreements in respect of related party transactions [member]	Member			ceo:TypesOfAgreementsInRespectOfRelatedPartyTransactionsMember
1401	Coalbed Methane Resources Exploration and Development Cooperation Agreement [member]	Member			ceo:CoalbedMethaneResourcesExplorationAndDevelopmentCooperationAgreementMember
1402	Range [axis]	Axis			ifrs-full:RangeAxis
1403	Ranges [member]	Member			ifrs-full:RangesMember
1404	Minimum [member]	Member			ifrs-full:BottomOfRangeMember
1405	Maximum [member]	Member			ifrs-full:TopOfRangeMember
1406	Categories of related parties [axis]	Axis			ifrs-full:CategoriesOfRelatedPartiesAxis
1407	Entity's total for related parties [member]	Member			ifrs-full:EntitysTotalForRelatedPartiesMember
1408	CNOOC Group [member]	Member			ceo:ChinaNationalOffshoreOilCorporationGroupMember
1409	CNOOC [member]	Member			ifrs-full:ParentMember
1410	Other related parties [member]	Member			ifrs-full:OtherRelatedPartiesMember
1411	CNOOC Finance Corporation Limited [member]	Member			ceo:CnoocFinanceCorporationLimitedMember
1412	A joint venture [member]	Member			ifrs-full:JointVenturesMember
1413	State-owned enterprises [member]	Member			ceo:StateownedEnterprisesMember
1414	China United Coalbed Methane Corporation Limited [member]	Member			ceo:ChinaUnitedCoalbedMethaneCorporationLimitedMember
1415	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
1416	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
1417	CNOOC International Limited [member]	Member			ceo:CnoocInternationalLimitedMember
1418	Disclosure of transactions between related parties [line items]	LineItems			ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesLineItems
1419	Provision of exploration, oil and gas development, oil and gas production as well as marketing, management and ancillary services by the CNOOC Group to the Group	Abstract			ceo:ProvisionOfExplorationOilAndGasDevelopmentOilAndGasProductionAsWellAsMarketingManagementAndAncillaryServicesByRelatedPartyAbstract
1420	Provision of exploration and support services	Concept (Monetary)	For Period	Debit	ifrs-full:ExpenseArisingFromExplorationForAndEvaluationOfMineralResources
1421	Inclusive of amounts capitalized under property, plant and equipment	Concept (Monetary)	For Period	Debit	ceo:ExpenseArisingFromExplorationForAndEvaluationOfMineralResourcesCapitalizedUnderPropertyPlantAndEquipment
1422	Provision of oil and gas development and support services	Concept (Monetary)	For Period	Debit	ceo:ExpenseArisingFromOilAndGasDevelopmentAndSupportServices
1423	Provision of oil and gas production and support services (note a)	Concept (Monetary)	For Period	Debit	ceo:ExpenseArisingFromOilAndGasProductionAndSupportServices
1424	Provision of marketing, management and ancillary services (note b)	Concept (Monetary)	For Period	Debit	ifrs-full:SellingGeneralAndAdministrativeExpense
1425	FPSO vessel leases (note c)	Concept (Monetary)	For Period		ifrs-full:LeasesAsLesseeRelatedPartyTransactions
1426	Total expenses arising from povision of exploration, oil and gas development, oil and gas production as well as marketing, management and ancillary services by the CNOOC Group to the Group	Concept (Monetary)	For Period	Debit	ifrs-full:ServicesReceivedRelatedPartyTransactions
1427	Sales of petroleum and natural gas products by the Group to the CNOOC Group	Abstract			ceo:SalesOfPetroleumAndNaturalGasProductsByRelatedPartyAbstract
1428	Sales of petroleum and natural gas products (other than long-term sales of natural gas and liquefied natural gas) (note d)	Concept (Monetary)	For Period	Credit	ceo:RevenueFromSalesOfPetroleumAndNaturalGasProductsOtherThanLongTermSalesOfNaturalGasAndLiquefiedNaturalGas
1429	Long term sales of natural gas and liquefied natural gas (note e)	Concept (Monetary)	For Period	Credit	ceo:RevenueFromLongTermSalesOfNaturalGasAndLiquefiedNaturalGas
1430	Total revenue from sales of petroleum and natural gas products by the Group to the CNOOC Group	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromSaleOfGoodsRelatedPartyTransactions
1431	Transactions and balances with CNOOC Finance Corporation Limited ("CNOOC Finance") (note f)	Abstract			ceo:TransactionsAndBalancesWithRelatedPartyAbstract
1432	Interest income received by the Group	Abstract			ceo:InterestIncomeReceivedFormRelatedPartyAbstract
1433	Interest income from deposits in CNOOC Finance	Concept (Monetary)	For Period	Credit	ifrs-full:InterestIncomeOnDeposits
1434	Deposits balances made by the Group	Abstract			ceo:DepositsFromRelatedPartyAbstract
1435	Deposits in CNOOC Finance	Concept (Monetary)	As Of	Debit	ceo:DepositsRelatedPartyTransactions
1436	Balances with the CNOOC Group	Abstract			ifrs-full:OutstandingBalancesForRelatedPartyTransactionsAbstract
1437	Amount due to CNOOC - included in other payables and accrued liabilities	Concept (Monetary)	As Of	Credit	ceo:OtherPayablesAndAccruedLiabilitiesDueToParentCompany
1438	Amount due to other related parties - included in trade and accrued payables	Concept (Monetary)	As Of	Credit	ceo:TradeAndAccruedPayablesDueToOtherRelatedParties
1439	Amounts payable, related party transactions	Concept (Monetary)	As Of	Credit	ifrs-full:AmountsPayableRelatedPartyTransactions
1440	Borrowings from CNOOC (note g)	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
1441	Amounts due from other related parties - included in trade receivables	Concept (Monetary)	As Of	Debit	ifrs-full:TradeReceivables
1442	Amounts due from other related parties - included in other current assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherCurrentAssets
1443	Amounts receivable, related party transactions	Concept (Monetary)	As Of	Debit	ifrs-full:AmountsReceivableRelatedPartyTransactions
1444	Balance with a joint venture	Abstract			ceo:OutstandingBalancesWithJointVenturesAbstract
1445	Amount due from a joint venture - included in other current assets	Concept (Monetary)	As Of	Debit	ceo:OtherCurrentAssetsDueFromJointVentures
1446	Transactions and balances with other state-owned enterprises	Abstract			ceo:TransactionsAndBalancesWithOtherStateownedEnterprisesAbstract
1447	Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
1448	Time deposits with maturity over three months	Concept (Monetary)	As Of	Debit	ifrs-full:ShorttermDepositsNotClassifiedAsCashEquivalents
1449	Specified dismantlement fund accounts (note 18)	Concept (Monetary)	As Of	Debit	ceo:SpecifiedDismantlementFund
1450	Total cash in bank and time deposits with certain state-owned banks in the PRC	Concept (Monetary)	As Of	Debit	ifrs-full:BalancesWithBanks
1451	Coalbed Methane Resources Exploration and Development Cooperation Agreement with China United Coalbed Methane Corporation Limited (note h)	Abstract			ceo:AccumulatedInvestmentWithRelatedPartyAbstract
1452	Accumulated investment	Concept (Monetary)	As Of	Debit	ceo:AccumulatedInvestmentUnsecuredInterestfreeAndAreRepayableOnDemand
1453	Term of long term sale contracts	Concept (xbrli:durationItemType)	For Period		ceo:TermOfLongTermSaleContracts
1454	Proportion of ownership interest in associate	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInAssociate
1455	Maximum daily outstanding balance for deposits from related parties	Concept (Monetary)	As Of	Debit	ceo:MaximumDailyOutstandingBalanceForDepositsFromRelatedParties
1456	Term of uncommitted revolving loan facility	Concept (xbrli:durationItemType)	For Period		ceo:TermOfUncommittedRevolvingLoanFacility
1457	Outstanding Principal Amount	Concept (Monetary)	As Of		ifrs-full:NotionalAmount
1458	Interest rate	Concept (Percent)	As Of		ifrs-full:BorrowingsInterestRate
1459	Withdrawal amount of the loan	Concept (Monetary)	As Of	Debit	ceo:WithdrawalAmountOfUncommiteedRevolvingLoanFacility
1460	43001 - Disclosure - RETIREMENT BENEFITS (Details)	Network	*	*	http://www.cnoocltd.com/role/RetirementBenefitsDetails
1461	Disclosure of retirement benefits	Table	*	*	ceo:DisclosureOfRetirementBenefitsTable
1462	Types of retirement benefits [axis]	Axis			ceo:TypesOfRetirementBenefitsAxis
1463	Types of retirement benefits [member]	Member			ceo:TypesOfRetirementBenefitsMember
1464	State-managed retirement benefit plan [member]	Member			ceo:StatemanagedRetirementBenefitPlanMember
1465	Defined contribution mandatory provident fund [member]	Member			ceo:DefinedContributionMandatoryProvidentFundMember
1466	Range [axis]	Axis			ifrs-full:RangeAxis
1467	Ranges [member]	Member			ifrs-full:RangesMember
1468	Minimum [member]	Member			ifrs-full:BottomOfRangeMember
1469	Maximum [member]	Member			ifrs-full:TopOfRangeMember
1470	All countries [axis]	Axis			ceo:AllCountriesAxis
1471	All countries [domain]	Member			country:AllCountriesDomain
1472	PRC [member]	Member			country:CN
1473	Hong Kong [member]	Member			country:HK
1474	Disclosure of retirement benefits	LineItems			ceo:DisclosureOfRetirementBenefitsLineItems
1475	Ratio of contribution to salaries of employees	Concept (Percent)	As Of		ceo:RatioOfContributionToSalariesOfEmployees
1476	Pension costs charged to the consolidated statement of profit or loss and other comprehensive income	Concept (Monetary)	For Period	Debit	ifrs-full:PostemploymentBenefitExpenseDefinedContributionPlans
1477	43101 - Disclosure - NOTE TO THE CONSOLIDATED STATEMENT OF CASH FLOWS (Details)	Network	*	*	http://www.cnoocltd.com/role/NoteToTheConsolidatedStatementOfCashFlowsDetails
1478	Implied Table	Table	*	*	implied:Table
1479	NOTE TO THE CONSOLIDATED STATEMENT OF CASH FLOWS [abstract]	Abstract			ceo:NoteToConsolidatedStatementOfCashFlowsAbstract
1480	Reconciliation of (loss)/profit before tax to cash generated from operations	Abstract			ceo:ReconciliationOfProfitLossBeforeTaxToCashGeneratedFromOperationsAbstract
1481	Profit (loss) before tax	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossBeforeTax
1482	Adjustments for:	Abstract			ifrs-full:AdjustmentsForReconcileProfitLossAbstract
1483	Interest income	Concept (Monetary)	For Period	Credit	ifrs-full:AdjustmentsForInterestIncome
1484	Finance costs	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForFinanceCosts
1485	Exchange losses/(gains), net	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnExchangeDifferencesOnTranslationBeforeTax
1486	Share of losses/(profits) of associates	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfProfitLossOfAssociatesAccountedForUsingEquityMethod
1487	(Profit)/loss of a joint venture	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfProfitLossOfJointVenturesAccountedForUsingEquityMethod
1488	Investment income	Concept (Monetary)	For Period	Credit	ifrs-full:InvestmentIncome
1489	Impairment for property, plant and equipment	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForImpairmentLossReversalOfImpairmentLossRecognisedInProfitOrLossPropertyPlantAndEquipment
1490	Provision for other assets	Concept (Monetary)	For Period	Debit	ceo:AdjustmentsForImpairmentLossReversalOfImpairmentLossRecognisedInProfitOrLossOtherAssets
1491	Depreciation, depletion and amortization	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDepreciationAndAmortisationExpense
1492	Loss on disposal and write-off of property, plant and equipment	Concept (Monetary)	For Period	Credit	ifrs-full:AdjustmentsForGainLossOnDisposalsPropertyPlantAndEquipment
1493	Subtotal	Concept (Monetary)	For Period		ifrs-full:CashFlowsFromUsedInOperationsBeforeChangesInWorkingCapital
1494	Increase in trade receivables and other current assets	Concept (Monetary)	For Period	Debit	ceo:AdjustmentsForDecreaseIncreaseInTradeReceivablesAndOtherCurrentAssets
1495	Decrease in inventories and supplies	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDecreaseIncreaseInInventories
1496	Increase in trade and accrued payables, contract liabilities and other payables and accrued liabilities	Concept (Monetary)	For Period	Debit	ceo:AdjustmentsForDecreaseIncreaseInTradeAndOtherPayablesAccruedLiabilitiesContractLiabilities
1497	Cash generated from operations	Concept (Monetary)	For Period		ifrs-full:CashFlowsFromUsedInOperations
1498	43102 - Disclosure - NOTE TO THE CONSOLIDATED STATEMENT OF CASH FLOWS - RECONCILIATION OF LIABILITIES ARISING FROM FINANCING ACTIVITIES (Details)	Network	*	*	http://www.cnoocltd.com/role/NoteToTheConsolidatedStatementOfCashFlowsReconciliationOfLiabilitiesArisingFromFinancingActivitiesDetails
1499	Disclosure of reconciliation of liabilities arising from financing activities [table]	Table	*	*	ifrs-full:DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesTable
1500	Liabilities arising from financing activities [axis]	Axis			ifrs-full:LiabilitiesArisingFromFinancingActivitiesAxis
1501	Liabilities arising from financing activities [member]	Member			ifrs-full:LiabilitiesArisingFromFinancingActivitiesMember
1502	Loans and borrowings [member]	Member			ceo:LoansAndBorrowingsMember
1503	Interest payable [member]	Member			ceo:InterestPayableMember
1504	Dividend payable [member]	Member			ceo:DividendPayableMember
1505	Disclosure of reconciliation of liabilities arising from financing activities [line items]	LineItems			ifrs-full:DisclosureOfReconciliationOfLiabilitiesArisingFromFinancingActivitiesLineItems
1506	Liabilities arising from financing activities at beginning of period	Concept (Monetary)	As Of	Credit	ifrs-full:LiabilitiesArisingFromFinancingActivities
1507	Financing cash flows	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughFinancingCashFlowsLiabilitiesArisingFromFinancingActivities
1508	Foreign exchange translation	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughEffectOfChangesInForeignExchangeRatesLiabilitiesArisingFromFinancingActivities
1509	Finance costs	Concept (Monetary)	For Period	Debit	ifrs-full:FinanceCosts
1510	Unwinding of discount on provision for dismantlement (note 26)	Concept (Monetary)	For Period	Debit	ifrs-full:ExpenseDueToUnwindingOfDiscountOnProvisions
1511	Amount capitalized in property, plant and equipment (note 13)	Concept (Monetary)	For Period		ifrs-full:BorrowingCostsCapitalised
1512	Dividends declared	Concept (Monetary)	For Period	Credit	ceo:IncreaseDecreaseThroughDividendsDeclaredLiabilitiesArisingFromFinancingActivities
1513	Liabilities arising from financing activities at end of period	Concept (Monetary)	As Of	Credit	ifrs-full:LiabilitiesArisingFromFinancingActivities
1514	43201 - Disclosure - COMMITMENTS AND CONTINGENCIES - Capital commitments (Details)	Network	*	*	http://www.cnoocltd.com/role/CommitmentsAndContingenciesCapitalCommitmentsDetails
1515	Disclosure of capital commitments [table]	Table	*	*	ceo:DisclosureOfCapitalCommitmentsTable
1516	Categories of related parties [axis]	Axis			ifrs-full:CategoriesOfRelatedPartiesAxis
1517	Entity's total for related parties [member]	Member			ifrs-full:EntitysTotalForRelatedPartiesMember
1518	Related parties [member]	Member			ifrs-full:RelatedPartiesMember
1519	CNOOC Group [member]	Member			ceo:ChinaNationalOffshoreOilCorporationGroupMember
1520	A joint venture [member]	Member			ifrs-full:JointVenturesMember
1521	Disclosure of capital commitments [line items]	LineItems			ceo:DisclosureOfCapitalCommitmentsLineItems
1522	Capital commitments	Abstract			ifrs-full:CapitalCommitmentsAbstract
1523	Contracted, but not provided for	Concept (Monetary)	As Of	Credit	ifrs-full:ContractualCapitalCommitments
1524	Period of estimated payments included in capital commitments with respect to the Group's exploration and production licenses	Concept (xbrli:durationItemType)	For Period		ceo:PeriodOfEstimatedPaymentsIncludedInCapitalCommitmentsWithRespectToExplorationAndProductionLicenses
1525	Unutilized banking facilities	Concept (Monetary)	As Of	Credit	ifrs-full:UndrawnBorrowingFacilities
1526	43202 - Disclosure - COMMITMENTS AND CONTINGENCIES - Operating lease commitments (Details)	Network	*	*	http://www.cnoocltd.com/role/CommitmentsAndContingenciesOperatingLeaseCommitmentsDetails
1527	Disclosure of maturity analysis of operating lease payments [table]	Table	*	*	ifrs-full:DisclosureOfMaturityAnalysisOfOperatingLeasePaymentsTable
1528	Range [axis]	Axis			ifrs-full:RangeAxis
1529	Ranges [member]	Member			ifrs-full:RangesMember
1530	Minimum [member]	Member			ifrs-full:BottomOfRangeMember
1531	Maximum [member]	Member			ifrs-full:TopOfRangeMember
1532	Classes of assets [axis]	Axis			ifrs-full:ClassesOfAssetsAxis
1533	Assets [member]	Member			ifrs-full:ClassesOfAssetsMember
1534	Office properties	Member			ifrs-full:OfficeEquipmentMember
1535	Property plant and equipment	Member			ifrs-full:PropertyPlantAndEquipmentMember
1536	Maturity [axis]	Axis			ifrs-full:MaturityAxis
1537	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
1538	Not later than one year [member]	Member			ifrs-full:NotLaterThanOneYearMember
1539	Later than one year and not later than two years [member]	Member			ifrs-full:LaterThanOneYearAndNotLaterThanTwoYearsMember
1540	Later than two years and not later than five years [member]	Member			ifrs-full:LaterThanTwoYearsAndNotLaterThanFiveYearsMember
1541	Later than five years [member]	Member			ifrs-full:LaterThanFiveYearsMember
1542	Categories of related parties [axis]	Axis			ifrs-full:CategoriesOfRelatedPartiesAxis
1543	Entity's total for related parties [member]	Member			ifrs-full:EntitysTotalForRelatedPartiesMember
1544	Related parties [member]	Member			ifrs-full:RelatedPartiesMember
1545	CNOOC Group [member]	Member			ceo:ChinaNationalOffshoreOilCorporationGroupMember
1546	A joint venture [member]	Member			ifrs-full:JointVenturesMember
1547	Disclsoure of operating lease commitments	LineItems			ifrs-full:DisclosureOfMaturityAnalysisOfOperatingLeasePaymentsLineItems
1548	Lease term	Concept (xbrli:durationItemType)	For Period		ceo:LeaseTermOperatingLeaseCommitment
1549	Commitments due:	Abstract			ifrs-full:DisclosureOfFinanceLeaseAndOperatingLeaseByLesseeAbstract
1550	Total minimum lease payments under non-cancellable operating leases	Concept (Monetary)	As Of	Credit	ifrs-full:MinimumLeasePaymentsPayableUnderNoncancellableOperatingLease
1551	43301 - Disclosure - FINANCIAL INSTRUMENTS - Fair value of financial instruments - Narrative (Details)	Network	*	*	http://www.cnoocltd.com/role/FinancialInstrumentsFairValueOfFinancialInstrumentsDetails
1552	Implied Table	Table	*	*	implied:Table
1553	FINANCIAL INSTRUMENTS [abstract]	Abstract			ifrs-full:DisclosureOfFinancialInstrumentsAbstract
1554	Estimated fair value of the Group's long term guaranteed notes	Concept (Monetary)	As Of	Credit	ceo:EstimatedFairValueOfLongTermGuaranteedNotes
1555	43302 - Disclosure - FINANCIAL INSTRUMENTS - Fair value hierarchy - Assets (Details)	Network	*	*	http://www.cnoocltd.com/role/FinancialInstrumentsFairValueHierarchyAssetsDetails
1556	Disclosure of fair value measurement of assets [table]	Table	*	*	ifrs-full:DisclosureOfFairValueMeasurementOfAssetsTable
1557	Measurement [axis]	Axis			ifrs-full:MeasurementAxis
1558	Aggregated measurement [member]	Member			ifrs-full:AggregatedMeasurementMember
1559	At fair value [member]	Member			ifrs-full:AtFairValueMember
1560	Levels of fair value hierarchy [axis]	Axis			ifrs-full:LevelsOfFairValueHierarchyAxis
1561	All levels of fair value hierarchy [member]	Member			ifrs-full:AllLevelsOfFairValueHierarchyMember
1562	Level 1 [member]	Member			ifrs-full:Level1OfFairValueHierarchyMember
1563	Level 2 [member]	Member			ifrs-full:Level2OfFairValueHierarchyMember
1564	Level 3 [member]	Member			ifrs-full:Level3OfFairValueHierarchyMember
1565	Classes of assets [axis]	Axis			ifrs-full:ClassesOfAssetsAxis
1566	Assets [member]	Member			ifrs-full:ClassesOfAssetsMember
1567	Other financial assets-current [member]	Member			ceo:OtherCurrentFinancialAssetsMember
1568	Corporate wealth management products [member]	Member			ceo:CorporateWealthManagementProductsClassifiedAsOtherCurrentFinancialAssetsMember
1569	Money market funds [member]	Member			ceo:MoneyMarketFundsMember
1570	Equity investments [member]	Member			ifrs-full:EquityInvestmentsMember
1571	Non-publicly traded investments - current [member]	Member			ceo:CurrentNonpubliclyTradedInvestmentsMember
1572	Publicly traded investments-non current [member]	Member			ceo:NoncurrentPubliclyTradedInvestmentsMember
1573	Disclosure of fair value measurement of assets [line items]	LineItems			ifrs-full:DisclosureOfFairValueMeasurementOfAssetsLineItems
1574	Assets measured at fair value	Concept (Monetary)	As Of	Debit	ifrs-full:Assets
1575	43303 - Disclosure - FINANCIAL INSTRUMENTS - Fair value hierarchy - Transfer between different levels of fair value hierarchy (Details)	Network	*	*	http://www.cnoocltd.com/role/FinancialInstrumentsFairValueHierarchyTransferBetweenDifferentLevelsOfFairValueHierarchyDetails
1576	Implied Table	Table	*	*	implied:Table
1577	FINANCIAL INSTRUMENTS [abstract]	Abstract			ifrs-full:DisclosureOfFinancialInstrumentsAbstract
1578	Amounts transferred between different levels of fair value hierarchy	Concept (Monetary)	For Period	Debit	ceo:AmountsTransferredBetweenDifferentLevelsOfFairValueHierarchy
1579	43401 - Disclosure - CONCENTRATION OF CUSTOMERS (Details)	Network	*	*	http://www.cnoocltd.com/role/ConcentrationOfCustomersDetails
1580	Disclosure of major customers [table]	Table	*	*	ifrs-full:DisclosureOfMajorCustomersTable
1581	Major customers [axis]	Axis			ifrs-full:MajorCustomersAxis
1582	Customers [member]	Member			ifrs-full:MajorCustomersMember
1583	PetroChina Company Limited [member]	Member			ceo:PetrochinaCompanyLimitedMember
1584	China Petroleum and Chemical Corporation [member]	Member			ceo:ChinaPetroleumAndChemicalCorporationMember
1585	Phillips 66 [member]	Member			ceo:PhillipsSixtysixMember
1586	BP p.l.c. [member]	Member			ceo:BritishPetroleumCompanyPLCMember
1587	China National Chemical Corporation [member]	Member			ceo:ChinaNationalChemicalCorporationMember
1588	Royal Dutch Shell PLC [member]	Member			ceo:RoyalDutchShellPlcMember
1589	EOG Resources, Inc. [member]	Member			ceo:EogResourcesIncMember
1590	Disclosure of major customers [line items]	LineItems			ifrs-full:DisclosureOfMajorCustomersLineItems
1591	Revenue	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
1592	43501 - Disclosure - FINANCIAL RISK MANAGEMENT OBJECTIVES AND POLICIES - Credit risk (Details)	Network	*	*	http://www.cnoocltd.com/role/FinancialRiskManagementObjectivesAndPoliciesCreditRiskDetails
1593	Disclosure of nature and extent of risks arising from financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsTable
1594	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1595	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1596	Credit risk and management assessment [member]	Member			ifrs-full:CreditRiskMember
1597	Counterparties [axis]	Axis			ifrs-full:CounterpartiesAxis
1598	Counterparties [member]	Member			ifrs-full:CounterpartiesMember
1599	The Group's largest third-party customer [member]	Member			ceo:GroupsLargestThirdpartyCustomerMember
1600	The five largest third-party customers [member]	Member			ceo:FiveLargestThirdpartyCustomersMember
1601	Disclosure of nature and extent of risks arising from financial instruments [line items]	LineItems			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
1602	Carrying amounts of other receivables included in other current assets	Concept (Monetary)	As Of	Debit	ceo:CarryingAmountsOfOtherReceivablesIncludedInOtherCurrentAssets
1603	Times of reviewing limits and scoring attributed to counterparties per year	Concept (Integer)	For Period		ceo:TimesOfReviewingLimitsAndScoringAttributedToCounterpartiesPerYear
1604	Percentage of trade receivables, benchmark to measure concentration of credit risk	Concept (Percent)	For Period		ceo:PercentageOfTradeReceivablesBenchmarkToMeasureConcentrationOfCreditRisk
1605	43502 - Disclosure - FINANCIAL RISK MANAGEMENT OBJECTIVES AND POLICIES - Currency risk (Details)	Network	*	*	http://www.cnoocltd.com/role/FinancialRiskManagementObjectivesAndPoliciesCurrencyRiskDetails
1606	Disclosure of nature and extent of risks arising from financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsTable
1607	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1608	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1609	Market risk [member]	Member			ifrs-full:MarketRiskMember
1610	Currency risk [member]	Member			ifrs-full:CurrencyRiskMember
1611	Disclosure of nature and extent of risks arising from financial instruments [line items]	LineItems			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
1612	Percentage of depreciation in Renminbi against US dollars	Concept (Percent)	For Period		ceo:PercentageOfDepreciationInRenminbiAgainstUsDollars
1613	Percentage of appreciation in Renminbi against US dollars	Concept (Percent)	For Period		ceo:PercentageOfAppreciationInRenminbiAgainstUSDollars
1614	Percentage of Group's cash and cash equivalents and time deposits with maturity over three months denominated in Renminbi	Concept (Percent)	As Of		ceo:PercentageOfGroupsCashAndCashEquivalentsAndTimeDepositsWithMaturityOverThreeMonthsDenominatedInRenminbi
1615	Strengthening/weakening of RMB against US dollars	Concept (Percent)	For Period		ceo:PercentageOfChangeInForeignExchangeRateOfUsDollars
1616	Percentage of increase/decrease in the profit for the year	Concept (Percent)	For Period		ceo:PercentageOfChangeInProfitLoss
1617	Percentage of increase/decrease in the equity of the Group	Concept (Percent)	For Period		ceo:PercentageOfChangeInEquity
1618	43503 - Disclosure - FINANCIAL RISK MANAGEMENT OBJECTIVES AND POLICIES - Interest rate risk (Details)	Network	*	*	http://www.cnoocltd.com/role/FinancialRiskManagementObjectivesAndPoliciesInterestRateRiskDetails
1619	Disclosure of nature and extent of risks arising from financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsTable
1620	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1621	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1622	Market risk [member]	Member			ifrs-full:MarketRiskMember
1623	Interest rate risk [member]	Member			ifrs-full:InterestRateRiskMember
1624	Disclosure of nature and extent of risks arising from financial instruments [line items]	LineItems			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
1625	Percentage of Group's debts that interest rates are fixed	Concept (Percent)	As Of		ceo:PercentageOfGroupsDebtsThatInterestRatesAreFixed
1626	Weighted average term of Group's debt balance outstanding	Concept (xbrli:durationItemType)	For Period		ceo:WeightedAverageTermOfGroupsDebtBalanceOutstanding
1627	43504 - Disclosure - FINANCIAL RISK MANAGEMENT OBJECTIVES AND POLICIES - Liquidity risk (Details)	Network	*	*	http://www.cnoocltd.com/role/FinancialRiskManagementObjectivesAndPoliciesLiquidityRiskDetails
1628	Disclosure of nature and extent of risks arising from financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsTable
1629	Range [axis]	Axis			ifrs-full:RangeAxis
1630	Ranges [member]	Member			ifrs-full:RangesMember
1631	Maximum [member]	Member			ifrs-full:TopOfRangeMember
1632	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1633	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1634	Liquidity risk	Member			ifrs-full:LiquidityRiskMember
1635	Disclosure of nature and extent of risks arising from financial instruments [line items]	LineItems			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
1636	Settlement term of trade and accrued payables, other payables and accrued liabilities	Concept (xbrli:durationItemType)	For Period		ceo:SettlementTermOfTradeAndAccruedPayablesOtherPayablesAndAccruedLiabilities
1637	43505 - Disclosure - FINANCIAL RISK MANAGEMENT OBJECTIVES AND POLICIES - Capital management (Details)	Network	*	*	http://www.cnoocltd.com/role/FinancialRiskManagementObjectivesAndPoliciesCapitalManagementDetails
1638	Implied Table	Table	*	*	implied:Table
1639	FINANCIAL RISK MANAGEMENT OBJECTIVES AND POLICIES [abstract]	Abstract			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsAbstract
1640	Capital management	Abstract			ifrs-full:DisclosureOfObjectivesPoliciesAndProcessesForManagingCapitalAbstract
1641	Changes made in the objectives, policies or processes for managing capital	Concept (Text/String)	For Period		ifrs-full:DescriptionOfChangesInEntitysObjectivesPoliciesAndProcessesForManagingCapitalAndWhatEntityManagesAsCapital
1642	Interest-bearing debts	Concept (Monetary)	As Of	Credit	ifrs-full:DebtSecurities
1643	Equity attributable to owners of the parent	Concept (Monetary)	As Of	Credit	ifrs-full:EquityAttributableToOwnersOfParent
1644	Total capital	Concept (Monetary)	As Of	Credit	ceo:TotalCapitalFinancialRiskManagementObjectivesAndPolicies
1645	Gearing ratio	Concept (Percent)	As Of		ceo:DebtToCapitalRatio