Constellium N.V. (SEC Filing Page | XBRL Cloud Viewer | XBRL Instance)

Line	Label	Object Class	Period Type	Balance	Report ElementName
1	1001 - Document - Document and Entity Information	Network	*	*	http://www.constellium.com/taxonomy/role/DocumentandEntityInformation
2	Implied Table	Table	*	*	implied:Table
3	Document and entity information [abstract]	Abstract			cstm:DocumentAndEntityInformationAbstract
4	Document Type	Concept (Submission Type)	For Period		dei:DocumentType
5	Amendment Flag	Concept (Yes/No)	For Period		dei:AmendmentFlag
6	Document Period End Date	Concept (Date)	For Period		dei:DocumentPeriodEndDate
7	Document Fiscal Year Focus	Concept (Year)	For Period		dei:DocumentFiscalYearFocus
8	Document Fiscal Period Focus	Concept (Fiscal Period)	For Period		dei:DocumentFiscalPeriodFocus
9	Trading Symbol	Concept (Text/String)	For Period		dei:TradingSymbol
10	Entity Registrant Name	Concept (Text/String)	For Period		dei:EntityRegistrantName
11	Entity Central Index Key	Concept (CIK Number)	For Period		dei:EntityCentralIndexKey
12	Current Fiscal Year End Date	Concept (Month/Day)	For Period		dei:CurrentFiscalYearEndDate
13	Entity Well-known Seasoned Issuer	Concept (Yes/No)	For Period		dei:EntityWellKnownSeasonedIssuer
14	Entity Current Reporting Status	Concept (Yes/No)	For Period		dei:EntityCurrentReportingStatus
15	Entity Filer Category	Concept (Filer Category)	For Period		dei:EntityFilerCategory
16	Entity Shell Company	Concept (Yes/No)	For Period		dei:EntityShellCompany
17	Entity Emerging Growth Company	Concept (Yes/No)	For Period		dei:EntityEmergingGrowthCompany
18	Entity Common Stock, Shares Outstanding	Concept (Shares)	As Of		dei:EntityCommonStockSharesOutstanding
19	1003 - Statement - Consolidated Income Statement	Network	*	*	http://www.constellium.com/taxonomy/role/StatementOfComprehensiveIncomeProfitOrLossByFunctionOfExpense-310000
20	Implied Table	Table	*	*	implied:Table
21	Profit or loss [abstract]	Abstract			ifrs-full:IncomeStatementAbstract
22	Revenue	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
23	Cost of sales	Concept (Monetary)	For Period	Debit	ifrs-full:CostOfSales
24	Gross profit	Concept (Monetary)	For Period	Credit	ifrs-full:GrossProfit
25	Selling and administrative expenses	Concept (Monetary)	For Period	Debit	ifrs-full:SellingGeneralAndAdministrativeExpense
26	Research and development expenses	Concept (Monetary)	For Period	Debit	ifrs-full:ResearchAndDevelopmentExpense
27	Restructuring costs	Concept (Monetary)	For Period	Debit	ifrs-full:ExpenseOfRestructuringActivities
28	Other gains / (losses)-net	Concept (Monetary)	For Period	Credit	ifrs-full:OtherGainsLosses
29	(Loss) / Income from operations	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossFromOperatingActivities
30	Finance costs-net	Concept (Monetary)	For Period	Credit	ifrs-full:FinanceIncomeCost
31	Share of loss of joint-ventures	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfProfitLossOfJointVenturesAccountedForUsingEquityMethod
32	Income / (loss) before income tax	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossBeforeTax
33	Income tax expense	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
34	Net income / (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
35	Net income / (loss) attributable to:	Abstract			ifrs-full:ProfitLossAttributableToAbstract
36	Equity holders of Constellium	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossAttributableToOwnersOfParent
37	Non-controlling interests	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossAttributableToNoncontrollingInterests
38	Net income / (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
39	Earnings per share attributable to the equity holders of Constellium	Abstract			ifrs-full:EarningsPerShareAbstract
40	Basic	Concept (Share)	For Period		ifrs-full:BasicEarningsLossPerShare
41	Diluted	Concept (Share)	For Period		ifrs-full:DilutedEarningsLossPerShare
42	1004 - Statement - Consolidated Statement of Comprehensive Income / (Loss)	Network	*	*	http://www.constellium.com/taxonomy/role/StatementOfComprehensiveIncomeOCIComponentsPresentedNetOfTax-410000
43	Implied Table	Table	*	*	implied:Table
44	Statement of comprehensive income [abstract]	Abstract			ifrs-full:StatementOfComprehensiveIncomeAbstract
45	Net income / (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
46	Other comprehensive income / (loss):	Abstract			ifrs-full:OtherComprehensiveIncomeAbstract
47	Items that will not be reclassified subsequently to the consolidated income statement	Abstract			ifrs-full:ComponentsOfOtherComprehensiveIncomeThatWillNotBeReclassifiedToProfitOrLossNetOfTaxAbstract
48	Remeasurement on post-employment benefit obligations	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeBeforeTaxGainsLossesOnRemeasurementsOfDefinedBenefitPlans
49	Income tax on remeasurement on post-employment benefit obligations	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxRelatingToRemeasurementsOfDefinedBenefitPlansOfOtherComprehensiveIncome
50	Items that may be reclassified subsequently to the consolidated income statement	Abstract			ifrs-full:ComponentsOfOtherComprehensiveIncomeThatWillBeReclassifiedToProfitOrLossNetOfTaxAbstract
51	Cash flow hedges	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeBeforeTaxCashFlowHedges
52	Net investment hedges	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeBeforeTaxHedgesOfNetInvestmentsInForeignOperations
53	Income tax on hedges	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxRelatingToCashFlowHedgesOfOtherComprehensiveIncome
54	Currency translation differences	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncomeNetOfTaxExchangeDifferencesOnTranslation
55	Other comprehensive income / (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncome
56	Total comprehensive income / (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncome
57	Attributable to:	Abstract			ifrs-full:ComprehensiveIncomeAttributableToAbstract
58	Equity holders of Constellium	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncomeAttributableToOwnersOfParent
59	Non-controlling interests	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncomeAttributableToNoncontrollingInterests
60	Total comprehensive income / (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncome
61	1005 - Statement - Consolidated Statement of Financial Position	Network	*	*	http://www.constellium.com/taxonomy/role/StatementOfFinancialPositionCurrentNonCurrent-210000
62	Implied Table	Table	*	*	implied:Table
63	Statement of financial position [abstract]	Abstract			ifrs-full:StatementOfFinancialPositionAbstract
64	Assets	Abstract			ifrs-full:AssetsAbstract
65	Current assets	Abstract			ifrs-full:CurrentAssetsAbstract
66	Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
67	Trade receivables and other	Concept (Monetary)	As Of	Debit	ifrs-full:TradeAndOtherCurrentReceivables
68	Inventories	Concept (Monetary)	As Of	Debit	ifrs-full:Inventories
69	Other financial assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherCurrentFinancialAssets
70	Total current assets	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentAssets
71	Non-current assets	Abstract			ifrs-full:NoncurrentAssetsAbstract
72	Property, plant and equipment	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
73	Goodwill	Concept (Monetary)	As Of	Debit	ifrs-full:Goodwill
74	Intangible assets	Concept (Monetary)	As Of	Debit	ifrs-full:IntangibleAssetsOtherThanGoodwill
75	Investments accounted for under the equity method	Concept (Monetary)	As Of	Debit	ifrs-full:InvestmentAccountedForUsingEquityMethod
76	Deferred income tax assets	Concept (Monetary)	As Of	Debit	ifrs-full:DeferredTaxAssets
77	Trade receivables and other	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentReceivables
78	Other financial assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherNoncurrentFinancialAssets
79	Total non-current assets	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentAssets
80	Total Assets	Concept (Monetary)	As Of	Debit	ifrs-full:Assets
81	Liabilities	Abstract			ifrs-full:LiabilitiesAbstract
82	Current liabilities	Abstract			ifrs-full:CurrentLiabilitiesAbstract
83	Trade payables and other	Concept (Monetary)	As Of	Credit	ifrs-full:TradeAndOtherCurrentPayables
84	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:ShorttermBorrowings
85	Other financial liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:OtherCurrentFinancialLiabilities
86	Income tax payable	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentTaxLiabilities
87	Provisions	Concept (Monetary)	As Of	Credit	ifrs-full:OtherShorttermProvisions
88	Total current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentLiabilities
89	Non-current liabilities	Abstract			ifrs-full:NoncurrentLiabilitiesAbstract
90	Trade payables and other	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentPayables
91	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:LongtermBorrowings
92	Other financial liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:OtherNoncurrentFinancialLiabilities
93	Pension and other post-employment benefit obligations	Concept (Monetary)	As Of	Credit	ifrs-full:RecognisedLiabilitiesDefinedBenefitPlan
94	Provisions	Concept (Monetary)	As Of	Credit	ifrs-full:OtherLongtermProvisions
95	Deferred income tax liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredTaxLiabilities
96	Total non-current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentLiabilities
97	Total Liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:Liabilities
98	Equity	Abstract			ifrs-full:EquityAbstract
99	Share capital	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
100	Share premium	Concept (Monetary)	As Of	Credit	ifrs-full:SharePremium
101	Retained deficit and other reserves	Concept (Monetary)	As Of	Credit	ifrs-full:RetainedEarnings
102	Equity attributable to equity holders of Constellium	Concept (Monetary)	As Of	Credit	ifrs-full:EquityAttributableToOwnersOfParent
103	Non-controlling interests	Concept (Monetary)	As Of	Credit	ifrs-full:NoncontrollingInterests
104	Total Equity	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
105	Total Equity and Liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:EquityAndLiabilities
106	1006 - Statement - Consolidated Statement of Changes in Equity	Network	*	*	http://www.constellium.com/taxonomy/role/StatementOfChangesInEquity-610000
107	Statement of changes in equity [table]	Table	*	*	ifrs-full:StatementOfChangesInEquityTable
108	Components of equity [axis]	Axis			ifrs-full:ComponentsOfEquityAxis
109	Equity [member]	Member			ifrs-full:EquityMember
110	Share capital [member]	Member			ifrs-full:IssuedCapitalMember
111	Share premium [member]	Member			ifrs-full:SharePremiumMember
112	Re-measurement [member]	Member			ifrs-full:ReserveOfRemeasurementsOfDefinedBenefitPlansMember
113	Reserve of cash flow hedges and net investment hedges [member]	Member			cstm:ReserveOfCashFlowHedgesAndNetInvestmentHedgesMember
114	Foreign currency translation reserve [member]	Member			ifrs-full:ReserveOfExchangeDifferencesOnTranslationMember
115	Other reserves [member]	Member			ifrs-full:OtherReservesMember
116	Retained losses [member]	Member			ifrs-full:RetainedEarningsMember
117	Total Equity holders of Constellium [member]	Member			ifrs-full:EquityAttributableToOwnersOfParentMember
118	Non-controlling interests [member]	Member			ifrs-full:NoncontrollingInterestsMember
119	Retrospective application and retrospective restatement [axis]	Axis			ifrs-full:RetrospectiveApplicationAndRetrospectiveRestatementAxis
120	Restated [member]	Member			ifrs-full:RestatedMember
121	Change in accounting policies [member]	Member			ifrs-full:FinancialEffectOfChangesInAccountingPolicyMember
122	Restated [member]	Member			cstm:RestatedBalanceMember
123	Statement of changes in equity [line items]	LineItems			ifrs-full:StatementOfChangesInEquityLineItems
124	Beginning balance	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
125	Change in accounting policies ending balance at Dec. 31,2018	Concept (Monetary)	For Period	Credit	ifrs-full:ChangesInEquity
126	Net income / (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
127	Other comprehensive income / (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncome
128	Total comprehensive income / (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncome
129	Share issuance	Concept (Monetary)	For Period	Credit	ifrs-full:IssueOfEquity
130	Transactions with equity holders Share-based compensation	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughSharebasedPaymentTransactions
131	Transactions with non-controlling interests	Concept (Monetary)	For Period	Credit	cstm:TransactionWithNoncontrollingInterests
132	Ending balance	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
133	1007 - Statement - Consolidated Statement of Cash Flows	Network	*	*	http://www.constellium.com/taxonomy/role/StatementOfCashFlowsIndirectMethod-520000
134	Implied Table	Table	*	*	implied:Table
135	Statement of cash flows [abstract]	Abstract			ifrs-full:StatementOfCashFlowsAbstract
136	Net income / (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
137	Adjustments	Abstract			ifrs-full:AdjustmentsForReconcileProfitLossAbstract
138	Depreciation and amortization	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDepreciationAndAmortisationExpense
139	Finance costs-net	Concept (Monetary)	For Period	Credit	ifrs-full:AdjustmentsForFinanceIncomeCost
140	Income tax expense	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForIncomeTaxExpense
141	Share of loss of joint-ventures	Concept (Monetary)	For Period	Credit	cstm:AdjustmentForShareOfProfitLossOfJointVentureAccountedForUsingEquityMethod
142	Unrealized losses / (gains) on derivatives-net and from remeasurement of monetary assets and liabilities-net	Concept (Monetary)	For Period	Credit	ifrs-full:AdjustmentsForGainsLossesOnChangeInFairValueOfDerivatives
143	(Gains) / losses on disposal	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForLossesGainsOnDisposalOfNoncurrentAssets
144	Other - net	Concept (Monetary)	For Period	Debit	ifrs-full:OtherInflowsOutflowsOfCashClassifiedAsOperatingActivities
145	Interest paid	Concept (Monetary)	For Period	Credit	ifrs-full:InterestPaidClassifiedAsOperatingActivities
146	Income tax paid	Concept (Monetary)	For Period	Credit	ifrs-full:IncomeTaxesPaidClassifiedAsOperatingActivities
147	Change in trade working capital	Abstract			cstm:IncreaseDecreaseInTradeWorkingCapitalAbstract
148	Inventories	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDecreaseIncreaseInInventories
149	Trade receivables	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDecreaseIncreaseInTradeAndOtherReceivables
150	Trade payables	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForIncreaseDecreaseInTradeAndOtherPayables
151	Margin calls	Concept (Monetary)	For Period	Debit	cstm:AdjustmentsForMarginCalls
152	Change in provisions and pension obligations	Concept (Monetary)	For Period	Debit	cstm:AdjustmentsForChangeInProvisionsAndPensionObligations
153	Other working capital	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseInWorkingCapital
154	Net cash flows from operating activities	Concept (Monetary)	For Period		ifrs-full:CashFlowsFromUsedInOperatingActivities
155	Purchases of property, plant and equipment	Concept (Monetary)	For Period	Credit	ifrs-full:PurchaseOfPropertyPlantAndEquipmentClassifiedAsInvestingActivities
156	Acquisition of subsidiaries net of cash acquired	Concept (Monetary)	For Period	Credit	ifrs-full:CashFlowsUsedInObtainingControlOfSubsidiariesOrOtherBusinessesClassifiedAsInvestingActivities
157	Proceeds from disposals net of cash	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromLosingControlOfSubsidiariesOrOtherBusinessesClassifiedAsInvestingActivities
158	Equity contribution and loan to joint-ventures	Concept (Monetary)	For Period	Credit	cstm:EquityContributionAndLoanToJointVenturesClassifiedAsInvestingActivities
159	Other investing activities	Concept (Monetary)	For Period	Debit	ifrs-full:OtherInflowsOutflowsOfCashClassifiedAsInvestingActivities
160	Net cash flows used in investing activities	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromUsedInInvestingActivities
161	Net proceeds received from issuance of shares	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromIssueOfOrdinaryShares
162	Proceeds from issuance of Senior Notes	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromIssueOfBondsNotesAndDebentures
163	Repayment of Senior Notes	Concept (Monetary)	For Period	Credit	ifrs-full:RepaymentsOfBondsNotesAndDebentures
164	(Repayments) / proceeds from revolving credit facilities and other loans	Concept (Monetary)	For Period	Credit	cstm:RepaymentsAndProceedsFromRevolvingCreditFacilityAndOtherLoans
165	Payment of deferred financing costs and exit fees	Concept (Monetary)	For Period	Credit	cstm:PaymentOfDeferredFinancingCostsAndExitFees
166	Transactions with non-controlling interests	Concept (Monetary)	For Period	Credit	ifrs-full:DividendsPaidToNoncontrollingInterestsClassifiedAsFinancingActivities
167	Other financing activities	Concept (Monetary)	For Period	Debit	ifrs-full:OtherInflowsOutflowsOfCashClassifiedAsFinancingActivities
168	Net cash flows (used in) / from financing activities	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromUsedInFinancingActivities
169	Net (decrease) / increase in cash and cash equivalents	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseInCashAndCashEquivalentsBeforeEffectOfExchangeRateChanges
170	Cash and cash equivalents-beginning of year	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
171	Cash and cash equivalents classified as held for sale-beginning of year	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalentsClassifiedAsPartOfDisposalGroupHeldForSale
172	Effect of exchange rate changes on cash and cash equivalents	Concept (Monetary)	For Period	Debit	ifrs-full:EffectOfExchangeRateChangesOnCashAndCashEquivalents
173	Cash and cash equivalents-end of year	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalentsIfDifferentFromStatementOfFinancialPosition
174	1008 - Disclosure - General Information	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfGeneralInformationAboutFinancialStatementsExplanatory
175	Implied Table	Table	*	*	implied:Table
176	Text block [abstract]	Abstract			cstm:TextBlockAbstract
177	General Information	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfGeneralInformationAboutFinancialStatementsExplanatory
178	1009 - Disclosure - Summary of Significant Accounting Policies	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfSummaryOfSignificantAccountingPoliciesExplanatory
179	Implied Table	Table	*	*	implied:Table
180	Text block [abstract]	Abstract			cstm:TextBlockAbstract
181	Summary of Significant Accounting Policies	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfSummaryOfSignificantAccountingPoliciesExplanatory
182	1010 - Disclosure - Revenue	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsInformationAboutRelationshipBetweenDisclosureOfDisaggregatedRevenueFromContractsWithCustomersAndRevenueInformationForReportableSegmentsExplanatory
183	Implied Table	Table	*	*	implied:Table
184	Text block [abstract]	Abstract			cstm:TextBlockAbstract
185	Revenue	Concept (Text Block (HTML))	For Period		ifrs-full:InformationAboutRelationshipBetweenDisclosureOfDisaggregatedRevenueFromContractsWithCustomersAndRevenueInformationForReportableSegmentsExplanatory
186	1011 - Disclosure - Operating Segment Information	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfEntitysReportableSegmentsExplanatory
187	Implied Table	Table	*	*	implied:Table
188	Text block [abstract]	Abstract			cstm:TextBlockAbstract
189	Operating Segment Information	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfEntitysReportableSegmentsExplanatory
190	1012 - Disclosure - Information by Geographic Area	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfInformationByGeographicalAreaExplanatory
191	Implied Table	Table	*	*	implied:Table
192	Text block [abstract]	Abstract			cstm:TextBlockAbstract
193	Information by Geographic Area	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfInformationByGeographicalAreaExplanatory
194	1013 - Disclosure - Expenses by Nature	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfExpensesByNatureExplanatory
195	Implied Table	Table	*	*	implied:Table
196	Text block [abstract]	Abstract			cstm:TextBlockAbstract
197	Expenses by Nature	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfExpensesByNatureExplanatory
198	1014 - Disclosure - Employee Benefit Expenses	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfEmployeeBenefitsExplanatory
199	Implied Table	Table	*	*	implied:Table
200	Text block [abstract]	Abstract			cstm:TextBlockAbstract
201	Employee Benefit Expenses	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfEmployeeBenefitsExplanatory
202	1015 - Disclosure - Other Gains / (Losses)-Net	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfOtherGainsNetExplanatory
203	Implied Table	Table	*	*	implied:Table
204	Text block [abstract]	Abstract			cstm:TextBlockAbstract
205	Other Gains / (Losses)-Net	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfOtherGainsNetExplanatory
206	1016 - Disclosure - Currency Gains / (Losses)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfCurrencyGainsAndLossesExplanatory
207	Implied Table	Table	*	*	implied:Table
208	Text block [abstract]	Abstract			cstm:TextBlockAbstract
209	Currency Gains / (Losses)	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfCurrencyGainsAndLossesExplanatory
210	1017 - Disclosure - Finance Costs-Net	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfFinanceCostExplanatory
211	Implied Table	Table	*	*	implied:Table
212	Text block [abstract]	Abstract			cstm:TextBlockAbstract
213	Finance Costs-Net	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinanceCostExplanatory
214	1018 - Disclosure - Income Tax	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfIncomeTaxExplanatory
215	Implied Table	Table	*	*	implied:Table
216	Text block [abstract]	Abstract			cstm:TextBlockAbstract
217	Income Tax	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfIncomeTaxExplanatory
218	1019 - Disclosure - Earnings Per Share	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfEarningsPerShareExplanatory
219	Implied Table	Table	*	*	implied:Table
220	Text block [abstract]	Abstract			cstm:TextBlockAbstract
221	Earnings Per Share	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfEarningsPerShareExplanatory
222	1020 - Disclosure - Cash and Cash Equivalents	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfCashAndCashEquivalentsExplanatory
223	Implied Table	Table	*	*	implied:Table
224	Text block [abstract]	Abstract			cstm:TextBlockAbstract
225	Cash and Cash Equivalents	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfCashAndCashEquivalentsExplanatory
226	1021 - Disclosure - Trade Receivables and Other	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfTradeAndOtherReceivablesExplanatory
227	Implied Table	Table	*	*	implied:Table
228	Text block [abstract]	Abstract			cstm:TextBlockAbstract
229	Trade Receivables and Other	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfTradeAndOtherReceivablesExplanatory
230	1022 - Disclosure - Inventories	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfInventoriesExplanatory
231	Implied Table	Table	*	*	implied:Table
232	Text block [abstract]	Abstract			cstm:TextBlockAbstract
233	Inventories	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInventoriesExplanatory
234	1023 - Disclosure - Property, Plant and Equipment	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfPropertyPlantAndEquipmentExplanatory
235	Implied Table	Table	*	*	implied:Table
236	Text block [abstract]	Abstract			cstm:TextBlockAbstract
237	Property, Plant and Equipment	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfPropertyPlantAndEquipmentExplanatory
238	1024 - Disclosure - Intangible Assets (Including Goodwill)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfIntangibleAssetsAndGoodwillExplanatory
239	Implied Table	Table	*	*	implied:Table
240	Text block [abstract]	Abstract			cstm:TextBlockAbstract
241	Intangible Assets (Including Goodwill)	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfIntangibleAssetsAndGoodwillExplanatory
242	1025 - Disclosure - Investments Accounted for Under Equity Method	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfInvestmentsAccountedForUsingEquityMethodExplanatory
243	Implied Table	Table	*	*	implied:Table
244	Text block [abstract]	Abstract			cstm:TextBlockAbstract
245	Investments Accounted for Under Equity Method	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInvestmentsAccountedForUsingEquityMethodExplanatory
246	1026 - Disclosure - Deferred Income Taxes	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfDeferredIncomeTaxExplanatory
247	Implied Table	Table	*	*	implied:Table
248	Text block [abstract]	Abstract			cstm:TextBlockAbstract
249	Deferred Income Taxes	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfDeferredIncomeTaxExplanatory
250	1027 - Disclosure - Trade Payables and Other	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfTradeAndOtherPayablesExplanatory
251	Implied Table	Table	*	*	implied:Table
252	Text block [abstract]	Abstract			cstm:TextBlockAbstract
253	Trade Payables and Other	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfTradeAndOtherPayablesExplanatory
254	1028 - Disclosure - Borrowings	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfBorrowingsExplanatory
255	Implied Table	Table	*	*	implied:Table
256	Text block [abstract]	Abstract			cstm:TextBlockAbstract
257	Borrowings	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfBorrowingsExplanatory
258	1029 - Disclosure - Financial Instruments	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfFinancialInstrumentsExplanatory
259	Implied Table	Table	*	*	implied:Table
260	Text block [abstract]	Abstract			cstm:TextBlockAbstract
261	Financial Instruments	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinancialInstrumentsExplanatory
262	1030 - Disclosure - Financial Risk Management	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfFinancialRiskManagementExplanatory
263	Implied Table	Table	*	*	implied:Table
264	Text block [abstract]	Abstract			cstm:TextBlockAbstract
265	Financial Risk Management	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinancialRiskManagementExplanatory
266	1031 - Disclosure - Pensions and Other Post-employment Benefit Obligations	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfPensionAndOtherPostEmploymentBenefitExpenseExplanatory
267	Implied Table	Table	*	*	implied:Table
268	Text block [abstract]	Abstract			cstm:TextBlockAbstract
269	Pensions and Other Post-employment Benefit Obligations	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfPensionAndOtherPostEmploymentBenefitExpenseExplanatory
270	1032 - Disclosure - Provisions	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfProvisionsExplanatory
271	Implied Table	Table	*	*	implied:Table
272	Text block [abstract]	Abstract			cstm:TextBlockAbstract
273	Provisions	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfProvisionsExplanatory
274	1033 - Disclosure - Non Cash Investing & Financing Transactions	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfCashFlowStatementExplanatory
275	Implied Table	Table	*	*	implied:Table
276	Text block [abstract]	Abstract			cstm:TextBlockAbstract
277	Non Cash Investing & Financing Transactions	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfCashFlowStatementExplanatory
278	1034 - Disclosure - Share Capital	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfShareCapitalReservesAndOtherEquityInterestExplanatory
279	Implied Table	Table	*	*	implied:Table
280	Text block [abstract]	Abstract			cstm:TextBlockAbstract
281	Share Capital	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfShareCapitalReservesAndOtherEquityInterestExplanatory
282	1035 - Disclosure - Commitments	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfCommitmentsExplanatory
283	Implied Table	Table	*	*	implied:Table
284	Text block [abstract]	Abstract			cstm:TextBlockAbstract
285	Commitments	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfCommitmentsExplanatory
286	1036 - Disclosure - Related Parties	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfRelatedPartyExplanatory
287	Implied Table	Table	*	*	implied:Table
288	Text block [abstract]	Abstract			cstm:TextBlockAbstract
289	Related Parties	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfRelatedPartyExplanatory
290	1037 - Disclosure - Share-Based Compensation	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfSharebasedPaymentArrangementsExplanatory
291	Implied Table	Table	*	*	implied:Table
292	Text block [abstract]	Abstract			cstm:TextBlockAbstract
293	Share-Based Compensation	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfSharebasedPaymentArrangementsExplanatory
294	1038 - Disclosure - Subsidiaries and Operating Segments	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfInterestsInSubsidiariesExplanatory
295	Implied Table	Table	*	*	implied:Table
296	Investments accounted for using equity method [abstract]	Abstract			ifrs-full:InvestmentsAccountedForUsingEquityMethodAbstract
297	Subsidiaries and Operating Segments	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInterestsInSubsidiariesExplanatory
298	1039 - Disclosure - Parent Company	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfParentCompanyExplanatory
299	Implied Table	Table	*	*	implied:Table
300	Text block [abstract]	Abstract			cstm:TextBlockAbstract
301	Parent Company	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfParentCompanyExplanatory
302	1040 - Disclosure - Acquisition of Constellium-Bowling Green	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfBusinessCombinationsExplanatory
303	Implied Table	Table	*	*	implied:Table
304	Text block [abstract]	Abstract			cstm:TextBlockAbstract
305	Acquisition of Constellium-Bowling Green	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfBusinessCombinationsExplanatory
306	1041 - Disclosure - Subsequent Events	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfEventsAfterReportingPeriodExplanatory
307	Implied Table	Table	*	*	implied:Table
308	Text block [abstract]	Abstract			cstm:TextBlockAbstract
309	Subsequent Events	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfEventsAfterReportingPeriodExplanatory
310	1042 - Disclosure - Summary of Significant Accounting Policies (Policies)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfSummaryOfSignificantAccountingPoliciesExplanatoryPolicies
311	Implied Table	Table	*	*	implied:Table
312	Text block [abstract]	Abstract			cstm:TextBlockAbstract
313	Statement of compliance	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfStatementOfComplianceExplanatory
314	Application of new and revised IFRS	Concept (Text Block (HTML))	For Period		cstm:DescriptionOfAccountingPolicyForNewAndRevisedStandardsNotYetAdoptedExplanatory
315	New standards and interpretations not yet mandatorily applicable	Concept (Text Block (HTML))	For Period		cstm:DescriptionOfAccountingPolicyForNewAccountingStandardsAndInterpretationsNotYetMandatoryOrEarlyAdoptedExplanatory
316	Basis of preparation	Concept (Text Block (HTML))	For Period		cstm:DescriptionOfAccountingPolicyForBasisOfPreparation
317	Presentation of the operating performance of each operating segment and of the Group	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForSegmentReportingExplanatory
318	Basis of consolidation	Concept (Text Block (HTML))	For Period		cstm:DescriptionOfAccountingPolicyForBasisOfConsolidationExplanatory
319	Business combinations	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForBusinessCombinationsExplanatory
320	Cash-generating units	Concept (Text Block (HTML))	For Period		cstm:DescriptionOfAccountingPolicyForCashGeneratingUnitsExplanatory
321	Goodwill	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForGoodwillExplanatory
322	Impairment of goodwill	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForImpairmentOfNonfinancialAssetsExplanatory
323	Non-current assets (and disposal groups) classified as held for sale & Discontinued operations	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForNoncurrentAssetsOrDisposalGroupsClassifiedAsHeldForSaleAndDiscontinuedOperationsExplanatory
324	Foreign currency transactions and foreign operations	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForForeignCurrencyTranslationExplanatory
325	Research and development costs	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForResearchAndDevelopmentExpenseExplanatory
326	Other gains / (losses) - net	Concept (Text Block (HTML))	For Period		cstm:DescriptionOfAccountingPolicyForOtherGainsLossesNetExplanatory
327	Interest income and expense	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForInterestIncomeAndExpenseExplanatory
328	Share-based payment arrangements	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForSharebasedPaymentTransactionsExplanatory
329	Property, plant and equipment	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForPropertyPlantAndEquipmentExplanatory
330	Intangible assets	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForIntangibleAssetsOtherThanGoodwillExplanatory
331	Impairment of property, plant and equipment and intangible assets	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForImpairmentOfAssetsExplanatory
332	Derivatives financial instruments	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForDerivativeFinancialInstrumentsExplanatory
333	Leases	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForLeasesExplanatory
334	Inventories	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForMeasuringInventories
335	Trade account receivables	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForTradeAndOtherReceivablesExplanatory
336	Cash and cash equivalents	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForRestrictedCashAndCashEquivalentsExplanatory
337	Share capital	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForIssuedCapitalExplanatory
338	Trade payables	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForTradeAndOtherPayablesExplanatory
339	Provisions	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForProvisionsExplanatory
340	Pension, other post-employment benefits and other long-term employee benefits	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForEmployeeBenefitsExplanatory
341	Taxation	Concept (Text Block (HTML))	For Period		ifrs-full:DescriptionOfAccountingPolicyForIncomeTaxExplanatory
342	Presentation of financial statements	Concept (Text Block (HTML))	For Period		cstm:DescriptionOfAccountingPolicyForPresentationOfFinancialStatementsExplanatory
343	Judgments in applying accounting policies and key sources of estimation uncertainty	Concept (Text Block (HTML))	For Period		cstm:DescriptionOfAccountingPolicyForUseOfJudgementsAndEstimatesExplanatory
344	1043 - Disclosure - Summary of Significant Accounting Policies (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfSummaryOfSignificantAccountingPoliciesExplanatoryTables
345	Implied Table	Table	*	*	implied:Table
346	Text block [abstract]	Abstract			cstm:TextBlockAbstract
347	Opening Financial Position Reclassification (IFRS 15 Standard)	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfReclassificationOfFinancialAssetsExplanatory
348	Disclosure of Foreign Exchange Rates	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfEffectOfChangesInForeignExchangeRatesExplanatory
349	1044 - Disclosure - Revenue (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsInformationAboutRelationshipBetweenDisclosureOfDisaggregatedRevenueFromContractsWithCustomersAndRevenueInformationForReportableSegmentsExplanatoryTables
350	Implied Table	Table	*	*	implied:Table
351	Text block [abstract]	Abstract			cstm:TextBlockAbstract
352	Summary of Revenue by Product Line	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfProductsAndServicesExplanatory
353	Disclosure of geographical areas	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfGeographicalAreasExplanatory
354	1045 - Disclosure - Operating Segment Information (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfEntitysReportableSegmentsExplanatoryTables
355	Implied Table	Table	*	*	implied:Table
356	Text block [abstract]	Abstract			cstm:TextBlockAbstract
357	Summary of Operating Segment Information	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfOperatingSegmentsExplanatory
358	Summary of Segment adjusted EBITDA and reconciliation of Adjusted EBITDA to Net Income	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfReconciliationOfSegmentProfitBeforeTaxAndProfitLossExplanatory
359	Summary of Segment Capital Expenditures	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfSegmentCapitalExpendituresExplanatory
360	Summary of Segment Assets	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfSegmentAssetsExplanatory
361	1046 - Disclosure - Information by Geographic Area (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfInformationByGeographicalAreaExplanatoryTables
362	Implied Table	Table	*	*	implied:Table
363	Text block [abstract]	Abstract			cstm:TextBlockAbstract
364	Summary of Property, Plant and Equipment Reported Based on Physical Location of Assets	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfPropertyPlantAndEquipmentReportedBasedOnPhysicalLocationOfAssetsExplanatory
365	1047 - Disclosure - Expenses by Nature (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfExpensesByNatureExplanatoryTables
366	Implied Table	Table	*	*	implied:Table
367	Text block [abstract]	Abstract			cstm:TextBlockAbstract
368	Detailed Information about Expenses by Nature	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfDetailedInformationAboutExpensesByNatureExplanatory
369	1048 - Disclosure - Employee Benefit Expenses (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfEmployeeBenefitsExplanatoryTables
370	Implied Table	Table	*	*	implied:Table
371	Text block [abstract]	Abstract			cstm:TextBlockAbstract
372	Summary of Employee Benefit Expenses	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDefinedBenefitPlansExplanatory
373	1049 - Disclosure - Other Gains / (Losses)-Net (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfOtherGainsNetExplanatoryTables
374	Implied Table	Table	*	*	implied:Table
375	Text block [abstract]	Abstract			cstm:TextBlockAbstract
376	Summary of Other Gains/(Losses) Net	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfDetailedInformationOtherGainsAndLossesExplanatory
377	1050 - Disclosure - Currency Gains / (Losses) (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfCurrencyGainsAndLossesExplanatoryTables
378	Implied Table	Table	*	*	implied:Table
379	Text block [abstract]	Abstract			cstm:TextBlockAbstract
380	Summary of Currency Gains and Losses Included in Income from Operations	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfCurrencyGainsAndLossesIncludedInIncomeLossFromOperationsExplanatoryTextBlock
381	Summary of Foreign Currency Translation Reserve	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfCurrencyTranslationReserveExplanatory
382	1051 - Disclosure - Finance Costs-Net (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfFinanceCostExplanatoryTables
383	Implied Table	Table	*	*	implied:Table
384	Text block [abstract]	Abstract			cstm:TextBlockAbstract
385	Summary of Finance Costs-Net	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinanceIncomeExpenseExplanatory
386	1052 - Disclosure - Income Tax (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfIncomeTaxExplanatoryTables
387	Implied Table	Table	*	*	implied:Table
388	Text block [abstract]	Abstract			cstm:TextBlockAbstract
389	Summary of Current and Deferred Components of Income Tax	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDeferredTaxesExplanatory
390	Summary of Income Tax Reconciliation Using Composite Statutory Income Tax Rate Applicable by Tax Jurisdiction	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsExplanatory
391	1053 - Disclosure - Earnings Per Share (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfEarningsPerShareExplanatoryTables
392	Implied Table	Table	*	*	implied:Table
393	Text block [abstract]	Abstract			cstm:TextBlockAbstract
394	Earning Per Share	Concept (Text Block (HTML))	For Period		ifrs-full:EarningsPerShareExplanatory
395	1054 - Disclosure - Cash and Cash Equivalents (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfCashAndCashEquivalentsExplanatoryTables
396	Implied Table	Table	*	*	implied:Table
397	Text block [abstract]	Abstract			cstm:TextBlockAbstract
398	Summary of Cash and Cash Equivalents	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfDetailedInformationOfCashAndCashEquivalentsExplanatory
399	1055 - Disclosure - Trade Receivables and Other (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfTradeAndOtherReceivablesExplanatoryTables
400	Implied Table	Table	*	*	implied:Table
401	Text block [abstract]	Abstract			cstm:TextBlockAbstract
402	Summary of Trade Receivables and Other	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfDetailedInformationAboutTradeAndOtherReceivablesExplanatory
403	Summary of Contract Assets	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfAssetsRecognisedFromCostsToObtainOrFulfilContractsWithCustomersExplanatory
404	Summary of Ageing of Total Trade Receivables - Net	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinancialAssetsThatAreEitherPastDueOrImpairedExplanatory
405	Summary of Carrying Amounts of Total Trade Receivables - Net by Currency	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfTradeReceivablesNetDenominatedInMajorCurrenciesTextBlock
406	1056 - Disclosure - Inventories (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfInventoriesExplanatoryTables
407	Implied Table	Table	*	*	implied:Table
408	Text block [abstract]	Abstract			cstm:TextBlockAbstract
409	Disclosure of Inventories	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfInformationAboutInventoriesExplanatory
410	1057 - Disclosure - Property, Plant and Equipment (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfPropertyPlantAndEquipmentExplanatoryTables
411	Implied Table	Table	*	*	implied:Table
412	Text block [abstract]	Abstract			cstm:TextBlockAbstract
413	Summary of Property Plant and Equipment	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDetailedInformationAboutPropertyPlantAndEquipmentExplanatory
414	Summary of Amounts Included in Building, Machinery and Equipment Under a Finance Lease	Concept (Text Block (HTML))	For Period		ifrs-full:ExplanationOfSignificantChangesInNetInvestmentInFinanceLeaseExplanatory
415	Summary of Future Aggregate Minimum Lease Payments Under Non-cancellable Finance Leases	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinanceLeaseAndOperatingLeaseByLesseeExplanatory
416	Summary of Total Depreciation Expense and Impairment Losses Relating to Property Plant and Equipment and Intangible Assets	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfDepreciationExpenseAndImpairmentLossesRelatingToPropertyPlantAndEquipmentAndIntangibleAssetsExplanatory
417	1058 - Disclosure - Intangible Assets (Including Goodwill) (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfIntangibleAssetsAndGoodwillExplanatoryTables
418	Implied Table	Table	*	*	implied:Table
419	Text block [abstract]	Abstract			cstm:TextBlockAbstract
420	Disclosure of Changes in Intangible Assets and Goodwill	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfReconciliationOfChangesInIntangibleAssetsAndGoodwillExplanatory
421	1059 - Disclosure - Investments Accounted for Under Equity Method (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfInvestmentsAccountedForUsingEquityMethodExplanatoryTables
422	Implied Table	Table	*	*	implied:Table
423	Text block [abstract]	Abstract			cstm:TextBlockAbstract
424	Summary of Investments Accounted for Under Equity Method	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInvestmentsOtherThanInvestmentsAccountedForUsingEquityMethodExplanatory
425	Summary of Share of Joint Ventures	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfJointOperationsExplanatory
426	Summary of Amounts Included in Consolidated Financial Statements in Accordance with Group Accounting Principles	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfReconciliationOfSummarisedFinancialInformationOfJointVentureAccountedForUsingEquityMethodToCarryingAmountOfInterestInJointVentureExplanatory
427	Summary of Guarantees and Commitments	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfInformationAboutLiquidityArrangementsGuaranteesOrOtherCommitmentsWithThirdPartiesThatMayAffectFairValueOrRiskOfInterestsInStructuredEntitiesExplanatory
428	1060 - Disclosure - Deferred Income Taxes (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfDeferredIncomeTaxExplanatoryTables
429	Implied Table	Table	*	*	implied:Table
430	Text block [abstract]	Abstract			cstm:TextBlockAbstract
431	Summary of Deferred Income Tax	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfDeferredIncomeTaxAssetsAndLiabilitiesExplanatory
432	Significant Components of Deferred Tax Assets and Liabilities	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfSignificantComponentsOfDeferredTaxAssetsAndLiabilitiesExplanatory
433	Components of Non Recognized Deferred Tax Assets	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfUnusedTaxLossesForWhichNoDeferredTaxAssetRecognisedExplanatory
434	1061 - Disclosure - Trade Payables and Other (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfTradeAndOtherPayablesExplanatoryTables
435	Implied Table	Table	*	*	implied:Table
436	Text block [abstract]	Abstract			cstm:TextBlockAbstract
437	Detailed Information about Trade Payables and Other	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfTradePayablesAndOtherExplanatory
438	Detailed information of contract liabilities	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfContractLiabilitiesExplanatory
439	1062 - Disclosure - Borrowings (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfBorrowingsExplanatoryTables
440	Implied Table	Table	*	*	implied:Table
441	Text block [abstract]	Abstract			cstm:TextBlockAbstract
442	Summary of Borrowings	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsExplanatory
443	Summary of Reconciliation of Movement in Net Borrowings Explanatory	Concept (Text Block (HTML))	For Period		cstm:ScheduleOfReconciliationOfMovementsInNetBorrowingsExplanatory
444	Summary of Composition of Carrying Amounts of Total Borrowings	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfDetailedInformationAboutCarryingAmountsAndMarketValuesOfBorrowingsExplanatory
445	1063 - Disclosure - Financial Instruments (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfFinancialInstrumentsExplanatoryTables
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448	Summary of Financial Assets and Liabilities by Categories	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFinancialInstrumentsAtFairValueThroughProfitOrLossExplanatory
449	Summary of Other Financial Assets and Other Financial Liabilities Positions	Concept (Text Block (HTML))	For Period		cstm:DisclosureOfFinancialDerivativeInstrumentAssetsAndLiabilitiesExplanatory
450	Summary of Derivatives Measured at Fair Value	Concept (Text Block (HTML))	For Period		ifrs-full:DisclosureOfFairValueMeasurementOfAssetsExplanatory
451	1064 - Disclosure - Financial Risk Management (Tables)	Network	*	*	http://www.constellium.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfFinancialRiskManagementExplanatoryTables
452	Statement [table]	Table	*	*	cstm:StatementTable
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454	All Currencies [Domain]	Member			currency:AllCurrenciesDomain
455	Non Us [member]	Member			cstm:NonUsMember
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695	Legal fees and lump-sum payments	Concept (Monetary)	For Period	Debit	cstm:LegalFees1
696	Collective bargaining agreement term	Concept (xbrli:durationItemType)	For Period		cstm:CollectiveBargainingAgreementsTerm
697	1086 - Disclosure - Operating Segment Information - Summary of Segment Capital Expenditures (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureOperatingSegmentInformationSummaryOfSegmentCapitalExpenditures
698	Disclosure of operating segments [table]	Table	*	*	ifrs-full:DisclosureOfOperatingSegmentsTable
699	Segments [axis]	Axis			ifrs-full:SegmentsAxis
700	Segments [member]	Member			ifrs-full:SegmentsMember
701	P&ARP [member]	Member			cstm:PackagingAndAutomotiveRolledProductsMember
702	A&T [member]	Member			cstm:AerospaceAndTransportationMember
703	AS&I [member]	Member			cstm:AutomotiveStructuresAndIndustryMember
704	Holdings & Corporate [member]	Member			cstm:HoldingsAndCorporateMember
705	Disclosure of operating segments [line items]	LineItems			ifrs-full:DisclosureOfOperatingSegmentsLineItems
706	Segment capital expenditures	Concept (Monetary)	For Period	Credit	ifrs-full:PurchaseOfPropertyPlantAndEquipmentClassifiedAsInvestingActivities
707	1087 - Disclosure - Operating Segment Information - Summary of Segment Assets (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureOperatingSegmentInformationSummaryOfSegmentAssets
708	Disclosure of operating segments [table]	Table	*	*	ifrs-full:DisclosureOfOperatingSegmentsTable
709	Segment consolidation items [axis]	Axis			ifrs-full:SegmentConsolidationItemsAxis
710	Entity's total for segment consolidation items [member]	Member			ifrs-full:EntitysTotalForSegmentConsolidationItemsMember
711	Segment [member]	Member			ifrs-full:OperatingSegmentsMember
712	Unallocated amounts [member]	Member			ifrs-full:UnallocatedAmountsMember
713	Segments [axis]	Axis			ifrs-full:SegmentsAxis
714	Segments [member]	Member			ifrs-full:SegmentsMember
715	P&ARP [member]	Member			cstm:PackagingAndAutomotiveRolledProductsMember
716	A&T [member]	Member			cstm:AerospaceAndTransportationMember
717	AS&I [member]	Member			cstm:AutomotiveStructuresAndIndustryMember
718	Holdings & Corporate [member]	Member			cstm:HoldingsAndCorporateMember
719	Disclosure of operating segments [line items]	LineItems			ifrs-full:DisclosureOfOperatingSegmentsLineItems
720	Total Assets	Concept (Monetary)	As Of	Debit	ifrs-full:Assets
721	Deferred income tax assets	Concept (Monetary)	As Of	Debit	ifrs-full:DeferredTaxAssets
722	Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
723	Other financial assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherFinancialAssets
724	1088 - Disclosure - Information by Geographic Area - Summary of Physical Location of Property, Plant and Equipment (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureInformationByGeographicAreaSummaryOfPhysicalLocationOfPropertyPlantAndEquipment
725	Disclosure of detailed information about property, plant and equipment [table]	Table	*	*	ifrs-full:DisclosureOfPropertyPlantAndEquipmentTable
726	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
727	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
728	United States [member]	Member			country:US
729	France [member]	Member			country:FR
730	Germany [member]	Member			country:DE
731	Czech Republic [member]	Member			country:CZ
732	Other countries [member]	Member			cstm:OtherCountriesMember
733	Disclosure of detailed information about property, plant and equipment [line items]	LineItems			ifrs-full:DisclosureOfPropertyPlantAndEquipmentLineItems
734	Property, plant and equipment	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
735	1089 - Disclosure - Expenses by Nature - Summary of Information about Expenses by Nature (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureExpensesByNatureSummaryOfInformationAboutExpensesByNature
736	Implied Table	Table	*	*	implied:Table
737	Expenses by nature [abstract]	Abstract			ifrs-full:ExpenseByNatureAbstract
738	Raw materials and consumables used	Concept (Monetary)	For Period	Debit	ifrs-full:RawMaterialsAndConsumablesUsed
739	Employee benefit expenses	Concept (Monetary)	For Period	Debit	ifrs-full:EmployeeBenefitsExpense
740	Energy costs	Concept (Monetary)	For Period	Debit	ifrs-full:EnergyExpense
741	Sub-contractors	Concept (Monetary)	For Period	Debit	cstm:SubcontractorsExpense
742	Freight out costs	Concept (Monetary)	For Period	Debit	ifrs-full:TransportationExpense
743	Professional fees	Concept (Monetary)	For Period	Debit	ifrs-full:ProfessionalFeesExpense
744	Operating lease expenses	Concept (Monetary)	For Period	Debit	ifrs-full:RentalExpense
745	Depreciation and amortization	Concept (Monetary)	For Period	Debit	ifrs-full:DepreciationAndAmortisationExpense
746	Other operating expenses	Concept (Monetary)	For Period	Debit	ifrs-full:MiscellaneousOtherOperatingExpense
747	Other gains / (losses)-net	Concept (Monetary)	For Period	Credit	ifrs-full:OtherGainsLosses
748	Total operating expenses	Concept (Monetary)	For Period	Debit	ifrs-full:OperatingExpense
749	1090 - Disclosure - Employee Benefit Expenses - Summary of Employee Benefit Expenses (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureEmployeeBenefitExpensesSummaryOfEmployeeBenefitExpenses
750	Implied Table	Table	*	*	implied:Table
751	Classes of employee benefits expense [abstract]	Abstract			ifrs-full:ClassesOfEmployeeBenefitsExpenseAbstract
752	Wages and salaries	Concept (Monetary)	For Period	Debit	ifrs-full:WagesAndSalaries
753	Pension costs-defined benefit plans	Concept (Monetary)	For Period	Debit	ifrs-full:PostemploymentBenefitExpenseDefinedBenefitPlans
754	Other post-employment benefits	Concept (Monetary)	For Period	Debit	ifrs-full:OtherLongtermBenefits
755	Share-based compensation	Concept (Monetary)	For Period	Debit	ifrs-full:ExpenseFromSharebasedPaymentTransactionsWithEmployees
756	Total employee benefit expenses	Concept (Monetary)	For Period	Debit	ifrs-full:EmployeeBenefitsExpense
757	1091 - Disclosure - Other Gains / (Losses)-Net - Summary of Other Gains/(Losses) Net (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureOtherGainsLossesNetSummaryOfOtherGainsLossesNet
758	Implied Table	Table	*	*	implied:Table
759	Analysis of income and expense [abstract]	Abstract			ifrs-full:AnalysisOfIncomeAndExpenseAbstract
760	Realized gains / (losses) on derivatives	Concept (Monetary)	For Period	Credit	cstm:RealizedGainLossesOnDerivatives
761	Unrealized (losses) / gains on derivatives at fair value through profit and loss-net	Concept (Monetary)	For Period	Credit	cstm:UnrealizedGainsLossesOnChangeInFairValueOfDerivatives
762	Unrealized exchange (losses) / gains from the remeasurement of monetary assets and liabilities-net	Concept (Monetary)	For Period	Credit	cstm:UnrealizedExchangeGainsLossesFromRemeasurementOfMonetaryAssetsAndLiabilitiesNet
763	Gains on pension plan amendments	Concept (Monetary)	For Period	Credit	cstm:GainsLossesOnPensionPlanAmendments
764	Gains / (losses) on disposal	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnDisposalsOfNoncurrentAssets
765	Wise purchase price adjustment	Concept (Monetary)	For Period	Credit	cstm:AcquisitionPurchasePriceAdjustment
766	Other	Concept (Monetary)	For Period	Credit	cstm:MiscellaneousOtherGainsLosses
767	Total other gains / (losses)-net	Concept (Monetary)	For Period	Credit	ifrs-full:OtherGainsLosses
768	1092 - Disclosure - Other Gains / (Losses)-Net - Summary of Other Gains/(Losses) Net (Parenthetical) (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureOtherGainsLossesNetSummaryOfOtherGainsLossesNetParenthetical
769	Analysis of other gains losses [table]	Table	*	*	cstm:AnalysisOfOtherGainsLossesTable
770	Arrangements involving legal form of lease [axis]	Axis			ifrs-full:ArrangementsInvolvingLegalFormOfLeaseAxis
771	Arrangements involving legal form of lease [member]	Member			ifrs-full:ArrangementsInvolvingLegalFormOfLeaseMember
772	Disposal of leased assets [member]	Member			cstm:DisposalOfLeasedAssetsMember
773	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
774	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
775	Novelis [member]	Member			cstm:NovelisMember
776	Analysis of other gains losses [line items]	LineItems			cstm:AnalysisOfOtherGainsLossesLineItems
777	Gains / (Losses) on pension plans amendments	Concept (Monetary)	For Period	Credit	cstm:GainsLossesOnPensionPlanAmendments
778	Sale of assets	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromDisposalsOfPropertyPlantAndEquipmentIntangibleAssetsOtherThanGoodwillInvestmentPropertyAndOtherNoncurrentAssets
779	Net gain on sale of assets	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnDisposalsOfPropertyPlantAndEquipment
780	Cash payment received on acquisition	Concept (Monetary)	For Period	Credit	cstm:CashPaymentReceivedUponAcquisition
781	Gain net of costs on acquisition	Concept (Monetary)	For Period	Credit	cstm:AcquisitionPurchasePriceAdjustment
782	1093 - Disclosure - Currency Gains / (Losses) - Summary of Currency Gains and Losses Included in Income from Operations (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureCurrencyGainsLossesSummaryOfCurrencyGainsAndLossesIncludedInIncomeFromOperations
783	Analysis Of Income And Expense [table]	Table	*	*	cstm:AnalysisOfIncomeAndExpenseTable
784	Consolidated and separate financial statements [axis]	Axis			ifrs-full:ConsolidatedAndSeparateFinancialStatementsAxis
785	Consolidated [member]	Member			ifrs-full:ConsolidatedMember
786	Revenue [member]	Member			cstm:RevenueMember
787	Cost of sales [member]	Member			cstm:CostOfSales1Member
788	Other gains / (losses - net [member]	Member			cstm:OtherGainsAndLossesNetMember
789	Analysis of income and expense [line items]	LineItems			cstm:AnalysisOfIncomeAndExpenseLineItems
790	Currency gains /(losses)	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnExchangeDifferencesOnTranslationRecognisedInProfitOrLoss
791	Realized exchange gains / (losses) on foreign currency derivatives-net	Concept (Monetary)	For Period	Credit	cstm:RealizedGainsLossesOnForeignCurrencyDerivativesNet
792	Unrealized (losses) / gains on foreign currency derivatives-net	Concept (Monetary)	For Period	Credit	cstm:UnrealizedGainsLossesOnForeignCurrencyDerivativesNet
793	Exchange gains / (losses) from the remeasurement of monetary assets and liabilities-net	Concept (Monetary)	For Period		cstm:ExchangesGainsLossesFromRemeasurementOfMonetaryAssetsAndLiabilitiesNet
794	1094 - Disclosure - Currency Gains / (Losses) - Summary of Foreign Currency Translation Reserve (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureCurrencyGainsLossesSummaryOfForeignCurrencyTranslationReserve
795	Implied Table	Table	*	*	implied:Table
796	Movement in foreign currency translation reserve [abstract]	Abstract			cstm:MovementInForeignCurrencyTranslationReserveAbstract
797	Foreign currency translation reserve at January 1	Concept (Monetary)	As Of	Credit	ifrs-full:ReserveOfExchangeDifferencesOnTranslation
798	Effect of currency translation differences	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnExchangeDifferencesOnTranslationBeforeTax
799	Foreign currency translation reserve at December 31	Concept (Monetary)	As Of	Credit	ifrs-full:ReserveOfExchangeDifferencesOnTranslation
800	1095 - Disclosure - Finance Costs-Net - Summary of Finance Costs-Net (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinanceCostsNetSummaryOfFinanceCostsNet
801	Implied Table	Table	*	*	implied:Table
802	Analysis of income and expense [abstract]	Abstract			ifrs-full:AnalysisOfIncomeAndExpenseAbstract
803	Interest received	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueFromInterest
804	Finance income	Concept (Monetary)	For Period	Credit	ifrs-full:FinanceIncome
805	Interest expense on borrowings	Concept (Monetary)	For Period	Debit	ifrs-full:InterestExpenseOnBorrowings
806	Expenses on factoring arrangements	Concept (Monetary)	For Period	Debit	cstm:ExpensesOnFactoringArrangementsPaidOrPayable
807	Interest expense on finance leases	Concept (Monetary)	For Period	Debit	ifrs-full:InterestExpenseOnFinanceLeases
808	Net loss on settlement of debt	Concept (Monetary)	For Period	Credit	ifrs-full:GainLossArisingFromDifferenceBetweenCarryingAmountOfFinancialLiabilityExtinguishedAndConsiderationPaid
809	Realized and unrealized gains / (losses) on debt derivatives at fair value	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnChangeInFairValueOfDerivatives
810	Realized and unrealized exchange (losses) / gains on financing activities-net	Concept (Monetary)	For Period	Credit	cstm:RealizedAndUnrealizedExchangeGainsLossesOnFinancingActivitiesNet
811	Interest cost on pension and other benefits	Concept (Monetary)	For Period	Debit	cstm:InterestCostOnPensionAndEmployeeBenefits
812	Other finance expenses	Concept (Monetary)	For Period	Credit	ifrs-full:OtherFinanceIncomeCost
813	Capitalized borrowing costs	Concept (Monetary)	For Period	Credit	cstm:BorrowingCostsCapitalisedCredit
814	Finance expenses	Concept (Monetary)	For Period	Debit	ifrs-full:FinanceCosts
815	Finance costs-net	Concept (Monetary)	For Period	Credit	ifrs-full:FinanceIncomeCost
816	1096 - Disclosure - Finance Costs-Net - Summary of Finance Costs-Net (Parenthetical) (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinanceCostsNetSummaryOfFinanceCostsNetParenthetical
817	Analysis Of Income And Expense [table]	Table	*	*	cstm:AnalysisOfIncomeAndExpenseTable
818	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
819	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
820	Constellium N.V. Senior Notes [member]	Member			cstm:ConstelliumSeniorNotesMember
821	Muscle Shoals' Senior Notes [member]	Member			cstm:MuscleShoalsSeniorNotesMember
822	Revolving Credit Facility 1 [member]	Member			cstm:RevolvingCreditFacility1Member
823	Pan US ABL Facility [member]	Member			cstm:PanUSABLFacilityMember
824	Constellium UACJ loan modification [member]	Member			cstm:ConstelliumUACJLoanModificationMember
825	Analysis of income and expense [line items]	LineItems			cstm:AnalysisOfIncomeAndExpenseLineItems
826	Interest expense on debt instrument	Concept (Monetary)	For Period	Debit	ifrs-full:InterestExpenseOnDebtInstrumentsIssued
827	Net loss on settlement of debt	Concept (Monetary)	For Period	Credit	ifrs-full:GainLossArisingFromDifferenceBetweenCarryingAmountOfFinancialLiabilityExtinguishedAndConsiderationPaid
828	Exit fees	Concept (Monetary)	For Period	Debit	cstm:ExitFees
829	Other finance expense	Concept (Monetary)	For Period	Credit	ifrs-full:OtherFinanceIncomeCost
830	Capitalisation rate	Concept (Percent)	For Period		ifrs-full:CapitalisationRateOfBorrowingCostsEligibleForCapitalisation
831	1097 - Disclosure - Income Tax - Summary of Current and Deferred Components of Income Tax (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureIncomeTaxSummaryOfCurrentAndDeferredComponentsOfIncomeTax
832	Implied Table	Table	*	*	implied:Table
833	Major components of tax expense (income) [abstract]	Abstract			ifrs-full:MajorComponentsOfTaxExpenseIncomeAbstract
834	Current tax expense	Concept (Monetary)	For Period	Debit	ifrs-full:CurrentTaxExpenseIncome
835	Deferred tax expense	Concept (Monetary)	For Period	Debit	ifrs-full:DeferredTaxExpenseIncome
836	Income tax (expense) / benefit	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
837	1098 - Disclosure - Income Tax - Summary of Income Tax Reconciliation Using Composite Statutory Income Tax Rate Applicable by Tax Jurisdiction (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureIncomeTaxSummaryOfIncomeTaxReconciliationUsingCompositeStatutoryIncomeTaxRateApplicableByTaxJurisdiction
838	Implied Table	Table	*	*	implied:Table
839	Reconciliation of average effective tax rate and applicable tax rate [abstract]	Abstract			ifrs-full:ReconciliationOfAverageEffectiveTaxRateAndApplicableTaxRateAbstract
840	Income before income tax	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossBeforeTax
841	Composite statutory income tax rate applicable by tax jurisdiction	Concept (Percent)	For Period		ifrs-full:ApplicableTaxRate
842	Income tax (expense) / benefit calculated at composite statutory tax rate applicable by tax jurisdiction	Concept (Monetary)	For Period	Debit	ifrs-full:TaxExpenseIncomeAtApplicableTaxRate
843	Tax effect of:	Abstract			ifrs-full:ReconciliationOfAccountingProfitMultipliedByApplicableTaxRatesAbstract
844	Changes in recognized and unrecognized deferred tax assets	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDeferredTaxExpense
845	Change in tax rate	Concept (Monetary)	For Period	Debit	ifrs-full:TaxEffectFromChangeInTaxRate
846	Other	Concept (Monetary)	For Period	Debit	ifrs-full:OtherTaxEffectsForReconciliationBetweenAccountingProfitAndTaxExpenseIncome
847	Income tax (expense) / benefit	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
848	Effective income tax rate	Concept (Percent)	For Period		ifrs-full:AverageEffectiveTaxRate
849	1099 - Disclosure - Income Tax - Summary of Income Tax Reconciliation Using Composite Statutory Income Tax Rate Applicable by Tax Jurisdiction (Parenthetical) (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureIncomeTaxSummaryOfIncomeTaxReconciliationUsingCompositeStatutoryIncomeTaxRateApplicableByTaxJurisdictionParenthetical
850	Disclosure of temporary difference, unused tax losses and unused tax credits [table]	Table	*	*	ifrs-full:DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsTable
851	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
852	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
853	United States [member]	Member			country:US
854	France [member]	Member			country:FR
855	Non-adjusting events after reporting period [axis]	Axis			ifrs-full:NonadjustingEventsAfterReportingPeriodAxis
856	Non-adjusting events after reporting period [member]	Member			ifrs-full:NonadjustingEventsMember
857	Changes in tax rates or tax laws enacted or announced [member]	Member			ifrs-full:ChangesInTaxRatesOrTaxLawsEnactedOrAnnouncedMember
858	Disclosure of tax reconciliation using composite statutory income tax rate applicable by tax jurisdictions [line Items]	LineItems			ifrs-full:DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems
859	Income tax rate	Concept (Percent)	For Period		ifrs-full:ApplicableTaxRate
860	Change in tax rate	Concept (Monetary)	For Period	Debit	ifrs-full:TaxEffectFromChangeInTaxRate
861	1100 - Disclosure - Income Tax - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureIncomeTaxAdditionalInformation
862	Disclosure of income tax expense [table]	Table	*	*	cstm:DisclosureOfIncomeTaxExpenseTable
863	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
864	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
865	United States [member]	Member			country:US
866	France [member]	Member			country:FR
867	Germany [member]	Member			country:DE
868	Netherlands [member]	Member			country:NL
869	Czech Republic [member]	Member			country:CZ
870	Disclosure of income tax expense [line Items]	LineItems			cstm:DisclosureOfIncomeTaxExpenseLineItems
871	Statutory income tax rate	Concept (Percent)	For Period		ifrs-full:ApplicableTaxRate
872	1101 - Disclosure - Earnings Per Share - Earnings Attributable to Equity Holders of Parent used to Calculate Basic and Diluted Earnings per share (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureEarningsPerShareEarningsAttributableToEquityHoldersOfParentUsedToCalculateBasicAndDilutedEarningsPerShare
873	Implied Table	Table	*	*	implied:Table
874	Earnings per share [abstract]	Abstract			ifrs-full:EarningsPerShareAbstract
875	Earnings attributable to equity holders of the parent used to calculate basic and diluted earnings per share	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossAttributableToOrdinaryEquityHoldersOfParentEntity
876	1102 - Disclosure - Earnings Per Share - Summary of Number of Shares Attributable to Equity Holders (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureEarningsPerShareSummaryOfNumberOfSharesAttributableToEquityHolders
877	Implied Table	Table	*	*	implied:Table
878	Weighted average ordinary shares and adjusted weighted average ordinary shares [abstract]	Abstract			ifrs-full:WeightedAverageSharesAndAdjustedWeightedAverageSharesAbstract
879	Weighted average number of ordinary shares used to calculate basic earnings per share	Concept (Shares)	For Period		ifrs-full:WeightedAverageShares
880	Effect of other dilutive potential ordinary shares	Concept (Shares)	For Period		ifrs-full:DilutiveEffectOfShareOptionsOnNumberOfOrdinaryShares
881	Weighted average number of ordinary shares used to calculate diluted earnings per share	Concept (Shares)	For Period		ifrs-full:AdjustedWeightedAverageShares
882	1103 - Disclosure - Earnings Per Share - Summary of Number of Shares Attributable to Equity Holders (Parenthetical) (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureEarningsPerShareSummaryOfNumberOfSharesAttributableToEquityHoldersParenthetical
883	Implied Table	Table	*	*	implied:Table
884	Weighted average ordinary shares and adjusted weighted average ordinary shares [abstract]	Abstract			ifrs-full:WeightedAverageSharesAndAdjustedWeightedAverageSharesAbstract
885	Potential Ordinary shares	Concept (Shares)	For Period		cstm:CalculationOfDilutedPotentialOrdinaryShares
886	1104 - Disclosure - Earnings Per Share - Summary of Earnings Per Share Attributable to the Equity Holders (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureEarningsPerShareSummaryOfEarningsPerShareAttributableToTheEquityHolders
887	Implied Table	Table	*	*	implied:Table
888	Earnings per share [abstract]	Abstract			ifrs-full:EarningsPerShareAbstract
889	Basic	Concept (Share)	For Period		ifrs-full:BasicEarningsLossPerShare
890	Diluted	Concept (Share)	For Period		ifrs-full:DilutedEarningsLossPerShare
891	1105 - Disclosure - Cash and Cash Equivalents - Summary of Cash and Cash Equivalents (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureCashAndCashEquivalentsSummaryOfCashAndCashEquivalents
892	Implied Table	Table	*	*	implied:Table
893	Cash and cash equivalents [abstract]	Abstract			ifrs-full:CashAndCashEquivalentsAbstract
894	Cash in bank and on hand	Concept (Monetary)	As Of	Debit	ifrs-full:Cash
895	Total Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
896	1106 - Disclosure - Cash and Cash Equivalents - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureCashAndCashEquivalentsAdditionalInformation
897	Disclosure of cash and cash equivalents [table]	Table	*	*	cstm:DisclosureOfCashAndCashEquivalentsTable
898	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
899	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
900	Subsidiaries in capital control restrictions countries [member]	Member			cstm:SubsidiariesInCapitalControlRestrictionsCountriesMember
901	Disclosure of cash and cash equivalents [line Items]	LineItems			cstm:DisclosureOfCashAndCashEquivalentsLineItems
902	Cash in bank and on hand	Concept (Monetary)	As Of	Debit	ifrs-full:Cash
903	1107 - Disclosure - Trade Receivables and Other - Summary of Trade Receivables and Other (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureTradeReceivablesAndOtherSummaryOfTradeReceivablesAndOther
904	Disclosure of trade and other receivables [table]	Table	*	*	cstm:DisclosureOfTradeAndOtherReceivablesTable
905	Carrying amount, accumulated depreciation, amortisation and impairment and gross carrying amount [axis]	Axis			ifrs-full:CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis
906	Carrying amount [member]	Member			ifrs-full:CarryingAmountMember
907	Gross value [member]	Member			ifrs-full:GrossCarryingAmountMember
908	Impairment [member]	Member			ifrs-full:AccumulatedImpairmentMember
909	Disclosure of trade and other receivables [line items]	LineItems			cstm:DisclosureOfTradeAndOtherReceivablesLineItems
910	Non-current trade receivables	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentTradeReceivables
911	Finance lease receivables	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentFinanceLeaseReceivables
912	Other taxes	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentTaxAssetsNoncurrent
913	Unbilled tooling costs	Concept (Monetary)	As Of	Debit	cstm:DeferredToolingRelatedCostsNonCurrent
914	Contract assets	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentContractAssets
915	Prepaid expenses	Concept (Monetary)	As Of	Debit	cstm:NoncurrentPrepaidExpenses
916	Restricted cash	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentRestrictedCashAndCashEquivalents
917	Other	Concept (Monetary)	As Of	Debit	cstm:OtherNoncurrentAssetsReceivables
918	Total Other receivables	Concept (Monetary)	As Of	Debit	cstm:OtherReceivablesNoncurrent
919	Total Trade receivables and Other	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentReceivables
920	Current trade receivables	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentTradeReceivables
921	Finance lease receivables	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentFinanceLeaseReceivables
922	Current income tax receivables	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentTaxAssetsCurrent
923	Other taxes	Concept (Monetary)	As Of	Debit	cstm:OtherTaxesReceivablesCurrent
924	Unbilled tooling costs	Concept (Monetary)	As Of	Debit	cstm:DeferredToolingRelatedCostsCurrent
925	Contract assets	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentContractAssets
926	Prepaid expenses	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentPrepaidExpenses
927	Restricted cash	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentRestrictedCashAndCashEquivalents
928	Other	Concept (Monetary)	As Of	Debit	cstm:OtherCurrentAssetsReceivables
929	Total Other receivables	Concept (Monetary)	As Of	Debit	ifrs-full:OtherCurrentReceivables
930	Total Trade receivables and Other	Concept (Monetary)	As Of	Debit	ifrs-full:TradeAndOtherCurrentReceivables
931	1108 - Disclosure - Trade Receivables and Other - Summary of Contract Assets (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureTradeReceivablesAndOtherSummaryOfContractAssets
932	Disclosure of disaggregation of revenue from contracts with customers [table]	Table	*	*	ifrs-full:DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersTable
933	Categories of assets recognised from costs to obtain or fulfil contracts with customers [axis]	Axis			ifrs-full:CategoriesOfAssetsRecognisedFromCostsToObtainOrFulfilContractsWithCustomersAxis
934	Categories of assets recognised from costs to obtain or fulfil contracts with customers [member]	Member			ifrs-full:CategoriesOfAssetsRecognisedFromCostsToObtainOrFulfilContractsWithCustomersMember
935	Unbilled Tooling Costs [member]	Member			cstm:UnbilledToolingCostsMember
936	Other Cost [member]	Member			cstm:OtherCostMember
937	Disclosure of disaggregation of revenue from contracts with customers [line items]	LineItems			ifrs-full:DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersLineItems
938	Non-current	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentContractAssets
939	Current	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentContractAssets
940	1109 - Disclosure - Trade Receivables and Other - Summary of Ageing of Total Trade Receivables - Net (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureTradeReceivablesAndOtherSummaryOfAgeingOfTotalTradeReceivablesNet
941	Aging of trade receivables [table]	Table	*	*	cstm:AgingOfTradeReceivablesTable
942	Past due status [axis]	Axis			ifrs-full:PastDueStatusAxis
943	Past due status [member]	Member			ifrs-full:PastDueStatusMember
944	Current [member]	Member			ifrs-full:CurrentMember
945	Past Due 1 to 30 Days [member]	Member			cstm:PastDueOneToThirtyDaysMember
946	Past Due 31 to 60 Days [member]	Member			ifrs-full:LaterThanOneMonthAndNotLaterThanTwoMonthsMember
947	Past Due 61 to 90 Days [member]	Member			ifrs-full:LaterThanTwoMonthsAndNotLaterThanThreeMonthsMember
948	Past Due Greater Than 91 Days [member]	Member			ifrs-full:LaterThanThreeMonthsMember
949	Trade receivables [line items]	LineItems			cstm:TradeReceivablesLineItems
950	Trade receivables-net	Concept (Monetary)	As Of	Debit	ifrs-full:TradeReceivables
951	1110 - Disclosure - Trade Receivables and Other - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureTradeReceivablesAndOtherAdditionalInformation
952	Disclosure of trade and other receivables [table]	Table	*	*	cstm:DisclosureOfTradeAndOtherReceivablesTable
953	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
954	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
955	France [member]	Member			country:FR
956	Germany Switzerland and Czech Republic [member]	Member			cstm:GermanySwitzerlandAndCzechRepublicMember
957	United States [member]	Member			country:US
958	Continuing involvement in derecognised financial assets by type of transfer [axis]	Axis			ifrs-full:ContinuingInvolvementInDerecognisedFinancialAssetsByTypeOfTransferAxis
959	Types of transfer [member]	Member			ifrs-full:TypesOfTransferMember
960	Factoring of receivables [member]	Member			ifrs-full:FactoringOfReceivablesMember
961	Factoring of receivables amendment [member]	Member			cstm:FactoringOfReceivablesAmendmentMember
962	Categories of related parties [axis]	Axis			ifrs-full:CategoriesOfRelatedPartiesAxis
963	Entity's total for related parties [member]	Member			ifrs-full:EntitysTotalForRelatedPartiesMember
964	Constellium automotive [member]	Member			cstm:ConstelliumAutomotiveMember
965	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
966	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
967	Muscle Shoals factoring facility [member]	Member			cstm:MuscleShoalsFactoringFacilityMember
968	Disclosure of trade and other receivables [line items]	LineItems			cstm:DisclosureOfTradeAndOtherReceivablesLineItems
969	Reversal of impairment allowance	Concept (Monetary)	For Period	Credit	ifrs-full:ReversalOfImpairmentLossRecognisedInProfitOrLossTradeReceivables
970	Factoring maximum capacity	Concept (Monetary)	For Period	Debit	cstm:FactoringMaximumCapacity
971	Trade receivable factoring agreement maturity date	Concept (Date)	For Period		cstm:AccountReceivableFactoringAgreementMaturityDate
972	Factored assets	Concept (Monetary)	As Of	Debit	cstm:FactoredAssetsDerecognizedAndRecognizedInConsolidatedStatementOfFinancialPosition
973	Factored assets, derecognized from Consolidated Statement of Financial Position	Concept (Monetary)	As Of	Debit	cstm:DerecognizedFactoredAssets
974	Factored assets, recognized in Consolidated Statement of Financial Position	Concept (Monetary)	As Of	Debit	cstm:FactoredAssetsRecognizedInConsolidatedStatementOfFinancialPosition
975	Debt due factor	Concept (Monetary)	As Of	Credit	cstm:DueToFactorRelatedToTradeAccountReceivablesSold
976	Finance lease receivables	Concept (Monetary)	As Of	Debit	ifrs-full:FinanceLeaseReceivables
977	1111 - Disclosure - Trade Receivables and Other - Summary of Carrying Amounts of Total Trade Receivables - Net by Currency (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureTradeReceivablesAndOtherSummaryOfCarryingAmountsOfTotalTradeReceivablesNetByCurrency
978	Trade receivables [table]	Table	*	*	cstm:TradeReceivablesTable
979	Currency [Axis]	Axis			srt:CurrencyAxis
980	All Currencies [Domain]	Member			currency:AllCurrenciesDomain
981	Euro [member]	Member			currency:EUR
982	U.S. Dollar [member]	Member			currency:USD
983	Swiss Franc [member]	Member			currency:CHF
984	Other currencies [member]	Member			cstm:OtherCurrenciesMember
985	Trade receivables [line items]	LineItems			cstm:TradeReceivablesLineItems
986	Total Trade receivables - net	Concept (Monetary)	As Of	Debit	ifrs-full:TradeReceivables
987	1112 - Disclosure - Inventories - Disclosure of Inventories (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureInventoriesDisclosureOfInventories
988	Implied Table	Table	*	*	implied:Table
989	Classes of current inventories [abstract]	Abstract			ifrs-full:ClassesOfInventoriesAbstract
990	Finished goods	Concept (Monetary)	As Of	Debit	ifrs-full:FinishedGoods
991	Work in progress	Concept (Monetary)	As Of	Debit	ifrs-full:WorkInProgress
992	Raw materials	Concept (Monetary)	As Of	Debit	ifrs-full:RawMaterials
993	Stores and supplies	Concept (Monetary)	As Of	Debit	ifrs-full:ProductionSupplies
994	Inventories write down	Concept (Monetary)	For Period		ifrs-full:InventoryWritedown2011
995	Total inventories	Concept (Monetary)	As Of	Debit	ifrs-full:Inventories
996	1113 - Disclosure - Property Plant and Equipment - Summary of Property Plant and Equipment (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosurePropertyPlantAndEquipmentSummaryOfPropertyPlantAndEquipment
997	Disclosure of detailed information about property, plant and equipment [table]	Table	*	*	ifrs-full:DisclosureOfPropertyPlantAndEquipmentTable
998	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
999	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
1000	Land and property rights.[member]	Member			cstm:LandAndPropertyRightsMember
1001	Buildings [member]	Member			ifrs-full:BuildingsMember
1002	Machinery and equipment [member]	Member			cstm:MachineryAndEquipment1Member
1003	Construction Work in Progress [member]	Member			ifrs-full:ConstructionInProgressMember
1004	Other [member]	Member			ifrs-full:OtherPropertyPlantAndEquipmentMember
1005	Carrying amount, accumulated depreciation, amortisation and impairment and gross carrying amount [axis]	Axis			ifrs-full:CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis
1006	Carrying amount [member]	Member			ifrs-full:CarryingAmountMember
1007	Gross value [member]	Member			ifrs-full:GrossCarryingAmountMember
1008	Accumulated depreciation [member]	Member			ifrs-full:AccumulatedDepreciationAndAmortisationMember
1009	Disclosure of detailed information about property, plant and equipment [line items]	LineItems			ifrs-full:DisclosureOfPropertyPlantAndEquipmentLineItems
1010	Net balance, beginning	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
1011	Additions	Concept (Monetary)	For Period	Debit	ifrs-full:AdditionsOtherThanThroughBusinessCombinationsPropertyPlantAndEquipment
1012	Disposals	Concept (Monetary)	For Period	Credit	ifrs-full:DisposalsPropertyPlantAndEquipment
1013	Depreciation expense	Concept (Monetary)	For Period		ifrs-full:DepreciationPropertyPlantAndEquipment
1014	Transfer during the year	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughTransfersPropertyPlantAndEquipment
1015	Effects of changes in foreign exchange rates	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughNetExchangeDifferencesPropertyPlantAndEquipment
1016	Net balance, ending	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
1017	1114 - Disclosure - Property Plant and Equipment - Summary of Amounts Included in Building, Machinery and Equipment Under a Finance Lease (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosurePropertyPlantAndEquipmentSummaryOfAmountsIncludedInBuildingMachineryAndEquipmentUnderAFinanceLease
1018	Disclosure of detailed information about property, plant and equipment [table]	Table	*	*	ifrs-full:DisclosureOfPropertyPlantAndEquipmentTable
1019	Carrying amount, accumulated depreciation, amortisation and impairment and gross carrying amount [axis]	Axis			ifrs-full:CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis
1020	Carrying amount [member]	Member			ifrs-full:CarryingAmountMember
1021	Gross value [member]	Member			ifrs-full:GrossCarryingAmountMember
1022	Accumulated depreciation [member]	Member			ifrs-full:AccumulatedDepreciationAndAmortisationMember
1023	Classes of property, plant and equipment [axis]	Axis			ifrs-full:ClassesOfPropertyPlantAndEquipmentAxis
1024	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
1025	Buildings [member]	Member			ifrs-full:BuildingsMember
1026	Machinery and equipment [member]	Member			cstm:MachineryAndEquipment1Member
1027	Disclosure of detailed information about property, plant and equipment [line items]	LineItems			ifrs-full:DisclosureOfPropertyPlantAndEquipmentLineItems
1028	Amounts included in Building/Machinery and Equipment under finance lease net	Concept (Monetary)	As Of	Debit	ifrs-full:RecognisedFinanceLeaseAsAssets
1029	1115 - Disclosure - Property Plant and Equipment - Summary of Future Aggregate Minimum Lease Payments Under Non-cancellable Finance Leases (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosurePropertyPlantAndEquipmentSummaryOfFutureAggregateMinimumLeasePaymentsUnderNoncancellableFinanceLeases
1030	Disclosure of finance lease and operating lease by lessee [table]	Table	*	*	ifrs-full:DisclosureOfFinanceLeaseAndOperatingLeaseByLesseeTable
1031	Maturity [axis]	Axis			ifrs-full:MaturityAxis
1032	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
1033	Less than 1 year [member]	Member			ifrs-full:NotLaterThanOneYearMember
1034	Expiring within 5 years [member]	Member			ifrs-full:LaterThanOneYearAndNotLaterThanFiveYearsMember
1035	More than 5 years [member]	Member			ifrs-full:LaterThanFiveYearsMember
1036	Disclosure of finance lease and operating lease by lessee [line items]	LineItems			ifrs-full:DisclosureOfFinanceLeaseAndOperatingLeaseByLesseeLineItems
1037	Future aggregate minimum lease payments under non-cancellable finance leases	Concept (Monetary)	As Of	Credit	ifrs-full:MinimumFinanceLeasePaymentsPayable
1038	Present value of future aggregate minimum lease payments under non-cancellable finance leases	Concept (Monetary)	As Of	Credit	ifrs-full:MinimumFinanceLeasePaymentsPayableAtPresentValue
1039	1116 - Disclosure - Property Plant and Equipment - Summary of Depreciation Expense and Impairment Losses Relating to Property Plant and Equipment and Intangible Assets (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosurePropertyPlantAndEquipmentSummaryOfDepreciationExpenseAndImpairmentLossesRelatingToPropertyPlantAndEquipmentAndIntangibleAssets
1040	Disclosure of detailed information about property, plant and equipment [table]	Table	*	*	ifrs-full:DisclosureOfPropertyPlantAndEquipmentTable
1041	Consolidated and separate financial statements [axis]	Axis			ifrs-full:ConsolidatedAndSeparateFinancialStatementsAxis
1042	Consolidated [member]	Member			ifrs-full:ConsolidatedMember
1043	Cost of sales [member]	Member			cstm:CostOfSales1Member
1044	Selling and administrative expenses [member]	Member			cstm:SellingAndAdministrativeExpenses1Member
1045	Research and development expenses [member]	Member			cstm:ResearchAndDevelopmentExpensesMember
1046	Disclosure of detailed information about property, plant and equipment [line items]	LineItems			ifrs-full:DisclosureOfPropertyPlantAndEquipmentLineItems
1047	Depreciation and Amortisation loss	Concept (Monetary)	For Period	Debit	ifrs-full:DepreciationAndAmortisationExpense
1048	1117 - Disclosure - Intangible Assets (Including Goodwill) - Disclosure of Changes in Intangible Assets and Goodwill (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureIntangibleAssetsIncludingGoodwillDisclosureOfChangesInIntangibleAssetsAndGoodwill
1049	Disclosure of reconciliation of changes in intangible assets and goodwill [table]	Table	*	*	ifrs-full:DisclosureOfReconciliationOfChangesInIntangibleAssetsAndGoodwillTable
1050	Classes of intangible assets and goodwill [axis]	Axis			ifrs-full:ClassesOfIntangibleAssetsAndGoodwillAxis
1051	Intangible assets and goodwill [member]	Member			ifrs-full:IntangibleAssetsAndGoodwillMember
1052	Technology [member]	Member			ifrs-full:TechnologybasedIntangibleAssetsMember
1053	Computer software [member]	Member			ifrs-full:ComputerSoftwareMember
1054	Customer relationships [member]	Member			cstm:CustomerRelationships1Member
1055	Work in progress [member]	Member			cstm:WorkInProgressMember
1056	Other intangible assets [member]	Member			ifrs-full:OtherIntangibleAssetsMember
1057	Carrying amount, accumulated depreciation, amortisation and impairment and gross carrying amount [axis]	Axis			ifrs-full:CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis
1058	Carrying amount [member]	Member			ifrs-full:CarryingAmountMember
1059	Gross value [member]	Member			ifrs-full:GrossCarryingAmountMember
1060	Accumulated amortization and impairment [member]	Member			ifrs-full:AccumulatedDepreciationAmortisationAndImpairmentMember
1061	Disclosure of reconciliation of changes in intangible assets and goodwill [line items]	LineItems			ifrs-full:DisclosureOfReconciliationOfChangesInIntangibleAssetsAndGoodwillLineItems
1062	Goodwill, beginning balance	Concept (Monetary)	As Of	Debit	ifrs-full:Goodwill
1063	Effects of changes in foreign exchange rates	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughNetExchangeDifferencesGoodwill
1064	Goodwill, ending balance	Concept (Monetary)	As Of	Debit	ifrs-full:Goodwill
1065	Intangible assets (excluding goodwill), beginning balance	Concept (Monetary)	As Of	Debit	ifrs-full:IntangibleAssetsOtherThanGoodwill
1066	Intangible assets (excluding goodwill), additions	Concept (Monetary)	For Period	Debit	ifrs-full:AdditionsOtherThanThroughBusinessCombinationsIntangibleAssetsOtherThanGoodwill
1067	Intangible assets (excluding goodwill), amortization expense	Concept (Monetary)	For Period		ifrs-full:AmortisationIntangibleAssetsOtherThanGoodwill
1068	Intangible assets (excluding goodwill), transfer during the period	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughTransfersIntangibleAssetsAndGoodwill
1069	Intangible assets (excluding goodwill), effects of changes in foreign exchange rates	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseThroughNetExchangeDifferencesIntangibleAssetsOtherThanGoodwill
1070	Intangible assets (excluding goodwill), ending balance	Concept (Monetary)	As Of	Debit	ifrs-full:IntangibleAssetsOtherThanGoodwill
1071	1118 - Disclosure - Intangible Assets (Including Goodwill) - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureIntangibleAssetsIncludingGoodwillAdditionalInformation
1072	Disclosure of reconciliation of changes in intangible assets and goodwill [table]	Table	*	*	ifrs-full:DisclosureOfReconciliationOfChangesInIntangibleAssetsAndGoodwillTable
1073	Segments [axis]	Axis			ifrs-full:SegmentsAxis
1074	Segments [member]	Member			ifrs-full:SegmentsMember
1075	P&ARP [member]	Member			cstm:PackagingAndAutomotiveRolledProductsMember
1076	A&T [member]	Member			cstm:AerospaceAndTransportationMember
1077	AS&I [member]	Member			cstm:AutomotiveStructuresAndIndustryMember
1078	Range [axis]	Axis			ifrs-full:RangeAxis
1079	Ranges [member]	Member			ifrs-full:RangesMember
1080	Bottom of range [member]	Member			ifrs-full:BottomOfRangeMember
1081	Top of range [member]	Member			ifrs-full:TopOfRangeMember
1082	Disclosure of reconciliation of changes in intangible assets and goodwill [line items]	LineItems			ifrs-full:DisclosureOfReconciliationOfChangesInIntangibleAssetsAndGoodwillLineItems
1083	Goodwill	Concept (Monetary)	As Of	Debit	ifrs-full:Goodwill
1084	Cash flow projected period	Concept (xbrli:durationItemType)	For Period		cstm:CashFlowProjectedPeriod
1085	Growth rate, cash flows projections	Concept (Percent)	As Of		ifrs-full:DescriptionOfGrowthRateUsedToExtrapolateCashFlowProjections
1086	Discount rate, cash flows projections	Concept (Percent)	As Of		ifrs-full:DescriptionOfDiscountRatesAppliedToCashFlowProjections
1087	Carrying value	Concept (Monetary)	As Of	Debit	cstm:CarryingValue
1088	Recoverable value	Concept (Monetary)	As Of	Debit	ifrs-full:RecoverableAmountOfAssetOrCashgeneratingUnit
1089	Increase discount rate	Concept (Percent)	For Period		cstm:IncreaseDiscountRate
1090	Decrease in the perpetual growth	Concept (Percent)	For Period		cstm:DecreaseInPerpetualGrowthRate
1091	Automotive Body Sheet lower shipments	Concept (Percent)	For Period		cstm:RecoverableValueEqualingCarryingPercentage
1092	1119 - Disclosure - Investments Accounted for Under Equity Method - Summary of Investments Accounted for Under Equity Method (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureInvestmentsAccountedForUnderEquityMethodSummaryOfInvestmentsAccountedForUnderEquityMethod
1093	Implied Table	Table	*	*	implied:Table
1094	Share of profit (loss) of associates and joint ventures accounted for using equity method [abstract]	Abstract			ifrs-full:ShareOfProfitLossOfAssociatesAndJointVenturesAccountedForUsingEquityMethodAbstract
1095	At January 1,	Concept (Monetary)	As Of	Debit	ifrs-full:InvestmentAccountedForUsingEquityMethod
1096	Joint venture's profit / (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfProfitLossOfJointVenturesAccountedForUsingEquityMethod
1097	Additions	Concept (Monetary)	For Period	Debit	cstm:InvestmentAccountedForUsingEquityMethodsAdditions
1098	Reclassified to non-current other financial assets	Concept (Monetary)	For Period	Debit	cstm:InvestmentAccountedForUsingEquityMethodReclassifiedToNoncurrentOtherFinancialAssets
1099	Effects of changes in foreign exchange rates	Concept (Monetary)	For Period	Debit	cstm:EffectOfForeignExchangeRate
1100	At December 31	Concept (Monetary)	As Of	Debit	ifrs-full:InvestmentAccountedForUsingEquityMethod
1101	1120 - Disclosure - Investments Accounted for Under Equity Method - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureInvestmentsAccountedForUnderEquityMethodAdditionalInformation
1102	Implied Table	Table	*	*	implied:Table
1103	Share of profit (loss) of associates and joint ventures accounted for using equity method [abstract]	Abstract			ifrs-full:ShareOfProfitLossOfAssociatesAndJointVenturesAccountedForUsingEquityMethodAbstract
1104	Cumulative share of losses of joint-ventures in excess of initial investment	Concept (Monetary)	For Period	Debit	cstm:CumulativeShareOfProfitLossOfJointVenturesAccountedForUsingEquityMethod
1105	Share of losses of joint-ventures in excess of initial investment	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfProfitLossOfJointVenturesAccountedForUsingEquityMethod
1106	1121 - Disclosure - Investments Accounted for Under Equity Method - Summary of Share of Joint Ventures (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureInvestmentsAccountedForUnderEquityMethodSummaryOfShareOfJointVentures
1107	Disclosure of joint ventures [table]	Table	*	*	ifrs-full:DisclosureOfJointVenturesTable
1108	Classes of assets [axis]	Axis			ifrs-full:ClassesOfAssetsAxis
1109	Assets [member]	Member			ifrs-full:ClassesOfAssetsMember
1110	Reclassified to non-current other financial assets [member]	Member			cstm:NoncurrentOtherFinancialAssetsMember
1111	Joint ventures [axis]	Axis			ifrs-full:JointVenturesAxis
1112	Entity's total for joint ventures [member]	Member			ifrs-full:EntitysTotalForJointVenturesMember
1113	Constellium-Bowling Green [member]	Member			cstm:ConstelliumUACJABSLLCMember
1114	Rhenaroll S.A. [member]	Member			cstm:RhenarollSaMember
1115	Group share [member]	Member			cstm:GroupShareInJointventuresMember
1116	Disclosure of joint ventures [line items]	LineItems			ifrs-full:DisclosureOfJointVenturesLineItems
1117	% interest	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInJointVenture
1118	Group share of joint venture's net assets	Concept (Monetary)	As Of	Debit	ifrs-full:InvestmentAccountedForUsingEquityMethod
1119	Group share of joint venture's profit / (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ShareOfProfitLossOfJointVenturesAccountedForUsingEquityMethod
1120	1122 - Disclosure - Investments Accounted for Under Equity Method - Summary of Share of Joint Ventures (Parenthetical) (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureInvestmentsAccountedForUnderEquityMethodSummaryOfShareOfJointVenturesParenthetical
1121	Disclosure of joint ventures [table]	Table	*	*	ifrs-full:DisclosureOfJointVenturesTable
1122	Joint ventures [axis]	Axis			ifrs-full:JointVenturesAxis
1123	Entity's total for joint ventures [member]	Member			ifrs-full:EntitysTotalForJointVenturesMember
1124	Constellium-Bowling Green [member]	Member			cstm:ConstelliumUACJABSLLCMember
1125	Rhenaroll S.A. [member]	Member			cstm:RhenarollSaMember
1126	Disclosure of joint ventures [line items]	LineItems			ifrs-full:DisclosureOfJointVenturesLineItems
1127	Ownership percentage	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInJointVenture
1128	Revenue	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
1129	1123 - Disclosure - Investments Accounted for Under Equity Method - Summary of Amounts Included in Consolidated Financial Statements in Accordance with Group Accounting Principles (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureInvestmentsAccountedForUnderEquityMethodSummaryOfAmountsIncludedInConsolidatedFinancialStatementsInAccordanceWithGroupAccountingPrinciples
1130	Disclosure of Investments Accounted for Using Equity Method [table]	Table	*	*	cstm:DisclosureOfInvestmentsAccountedForUsingEquityMethodTable
1131	Joint ventures [axis]	Axis			ifrs-full:JointVenturesAxis
1132	Entity's total for joint ventures [member]	Member			ifrs-full:EntitysTotalForJointVenturesMember
1133	Constellium-Bowling Green [member]	Member			cstm:ConstelliumUACJABSLLCMember
1134	Group Companies and Constellium UACJ ABS LLC [member]	Member			cstm:GroupCompaniesAndConstelliumUacjAbsLlcMember
1135	Disclosure of investments accounted for using equity method [line items]	LineItems			cstm:DisclosureOfInvestmentsAccountedForUsingEquityMethodLineItems
1136	Current assets	Abstract			ifrs-full:CurrentAssetsAbstract
1137	Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
1138	Trade receivables and other	Concept (Monetary)	As Of	Debit	ifrs-full:TradeAndOtherCurrentReceivables
1139	Inventories	Concept (Monetary)	As Of	Debit	ifrs-full:Inventories
1140	Other financial assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherFinancialAssets
1141	Revenue	Abstract			ifrs-full:RevenueAbstract
1142	Non-current assets	Abstract			ifrs-full:NoncurrentAssetsAbstract
1143	Property, plant and equipment	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
1144	Intangible assets	Concept (Monetary)	As Of	Debit	ifrs-full:IntangibleAssetsOtherThanGoodwill
1145	Total Assets	Concept (Monetary)	As Of	Debit	ifrs-full:Assets
1146	Current liabilities	Abstract			ifrs-full:CurrentLiabilitiesAbstract
1147	Trade payables and other	Concept (Monetary)	As Of	Credit	ifrs-full:TradeAndOtherCurrentPayables
1148	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:ShorttermBorrowings
1149	Non-current liabilities	Abstract			ifrs-full:NoncurrentLiabilitiesAbstract
1150	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:LongtermBorrowings
1151	Equity	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
1152	Total Equity and Liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:EquityAndLiabilities
1153	Revenue	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
1154	Cost of sales	Concept (Monetary)	For Period	Debit	ifrs-full:CostOfSales
1155	Selling and administrative expenses	Concept (Monetary)	For Period	Debit	ifrs-full:SellingGeneralAndAdministrativeExpense
1156	Fees and recharges	Concept (Monetary)	For Period	Credit	cstm:FeesAndRecharges
1157	(Loss) / Income from operations	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossFromOperatingActivities
1158	Finance income	Concept (Monetary)	For Period	Credit	cstm:FinanceIncomeLoss
1159	Finance costs	Concept (Monetary)	For Period	Debit	ifrs-full:FinanceCosts
1160	Net income / (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
1161	1124 - Disclosure - Investments Accounted for Under Equity Method - Summary of Amounts Included in Consolidated Financial Statements in Accordance with Group Accounting Principles (Parenthetical) (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureInvestmentsAccountedForUnderEquityMethodSummaryOfAmountsIncludedInConsolidatedFinancialStatementsInAccordanceWithGroupAccountingPrinciplesParenthetical
1162	Disclosure of Investments Accounted for Using Equity Method [table]	Table	*	*	cstm:DisclosureOfInvestmentsAccountedForUsingEquityMethodTable
1163	Joint ventures [axis]	Axis			ifrs-full:JointVenturesAxis
1164	Entity's total for joint ventures [member]	Member			ifrs-full:EntitysTotalForJointVenturesMember
1165	Group Companies and Constellium UACJ ABS LLC [member]	Member			cstm:GroupCompaniesAndConstelliumUacjAbsLlcMember
1166	Disclosure of investments accounted for using equity method [line items]	LineItems			cstm:DisclosureOfInvestmentsAccountedForUsingEquityMethodLineItems
1167	Gain related shareholders loan facilities modification	Concept (Monetary)	As Of	Debit	cstm:GainOnShareholdersLoanFacilitiesModification
1168	Loans	Concept (Monetary)	As Of	Debit	cstm:LoansToJointVentures
1169	Share of losses of joint-ventures in excess of initial investment	Concept (Monetary)	For Period	Debit	cstm:CumulativeShareOfProfitLossOfJointVenturesAccountedForUsingEquityMethod
1170	1125 - Disclosure - Investments Accounted for Under Equity Method - Summary of Guarantees and Commitments (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureInvestmentsAccountedForUnderEquityMethodSummaryOfGuaranteesAndCommitments
1171	Disclosure of joint ventures [table]	Table	*	*	ifrs-full:DisclosureOfJointVenturesTable
1172	Joint ventures [axis]	Axis			ifrs-full:JointVenturesAxis
1173	Entity's total for joint ventures [member]	Member			ifrs-full:EntitysTotalForJointVenturesMember
1174	Constellium-Bowling Green [member]	Member			cstm:ConstelliumUACJABSLLCMember
1175	Classes of financial instruments [axis]	Axis			ifrs-full:ClassesOfFinancialInstrumentsAxis
1176	Financial instruments, class [member]	Member			ifrs-full:ClassesOfFinancialInstrumentsMember
1177	Financial guarantees [member]	Member			cstm:FinancialGuaranteesMember
1178	Loan Facility Commitment [member]	Member			cstm:LoanFacilityCommitmentMember
1179	Supplier guarantees [member]	Member			cstm:SupplierGuaranteesMember
1180	Disclosure of joint ventures [line items]	LineItems			ifrs-full:DisclosureOfJointVenturesLineItems
1181	Total guarantees and commitments given	Concept (Monetary)	As Of	Credit	ifrs-full:CommitmentsInRelationToJointVentures
1182	1126 - Disclosure - Deferred Income Taxes - Summary of Deferred Income Taxes (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureDeferredIncomeTaxesSummaryOfDeferredIncomeTaxes
1183	Implied Table	Table	*	*	implied:Table
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1185	Deferred income tax assets	Concept (Monetary)	As Of	Debit	ifrs-full:DeferredTaxAssets
1186	Deferred income tax liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredTaxLiabilities
1187	Net deferred income tax assets	Concept (Monetary)	As Of	Debit	ifrs-full:NetDeferredTaxAssets
1188	1127 - Disclosure - Deferred Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureDeferredIncomeTaxesSignificantComponentsOfDeferredTaxAssetsAndLiabilities
1189	Significant components of deferred tax assets and liabilities [table]	Table	*	*	cstm:SignificantComponentsOfDeferredTaxAssetsAndLiabilitiesTable
1190	Assets and liabilities [axis]	Axis			ifrs-full:AssetsAndLiabilitiesAxis
1191	Assets and liabilities [member]	Member			ifrs-full:AssetsAndLiabilitiesMember
1192	Long-term assets [member]	Member			cstm:LongTermAssetsMember
1193	Inventories [member]	Member			cstm:InventoryMember
1194	Pensions [member]	Member			cstm:PensionsMember
1195	Derivative valuation [member]	Member			cstm:DerivativeValuationMember
1196	Tax losses carried forward [member]	Member			cstm:TaxLossesCarriedForwardMember
1197	Other [member]	Member			cstm:OtherDeferredTaxAssetsAndLiabilitiesMember
1198	Significant components of deferred tax assets and liabilities [line items]	LineItems			cstm:SignificantComponentsOfDeferredTaxAssetsAndLiabilitiesLineItems
1199	At January 1	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredTaxLiabilityAsset
1200	Recognized in Profit or loss	Concept (Monetary)	For Period		ifrs-full:DeferredTaxExpenseIncomeRecognisedInProfitOrLoss
1201	Recognized in OCI	Concept (Monetary)	For Period		ifrs-full:IncomeTaxRelatingToComponentsOfOtherComprehensiveIncome
1202	Effect of change in foreign exchange rates	Concept (Monetary)	For Period	Credit	ifrs-full:IncreaseDecreaseThroughNetExchangeDifferencesDeferredTaxLiabilityAsset
1203	At December 31	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredTaxLiabilityAsset
1204	1128 - Disclosure - Deferred Income Taxes - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureDeferredIncomeTaxesAdditionalInformation
1205	Significant components of deferred tax assets and liabilities [table]	Table	*	*	cstm:SignificantComponentsOfDeferredTaxAssetsAndLiabilitiesTable
1206	Geographical areas [axis]	Axis			ifrs-full:GeographicalAreasAxis
1207	Geographical areas [member]	Member			ifrs-full:GeographicalAreasMember
1208	Switzerland [member]	Member			country:CH
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1210	US tax rate decrease impact in P&L	Concept (Monetary)	For Period	Debit	cstm:IncreaseDecreaseInDeferredTaxRecognisedInProfitOrLossDueToChangeInRate
1211	US tax rate decrease impact in OCI	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseInAccumulatedDeferredTaxRecognisedInOtherComprehensiveIncomeDueToChangeInTaxRate
1212	Unused tax losses for which no deferred tax asset recognized	Concept (Monetary)	As Of		ifrs-full:UnusedTaxLossesForWhichNoDeferredTaxAssetRecognised
1213	Related tax impact	Concept (Monetary)	As Of	Debit	cstm:NonRecognizedTaxAssets
1214	Tax loss carried forwards	Concept (Monetary)	For Period	Credit	cstm:UnusedTaxLossesCarriedForward
1215	1129 - Disclosure - Deferred Income Taxes - Components of Non Recognized Deferred Tax Assets (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureDeferredIncomeTaxesComponentsOfNonRecognizedDeferredTaxAssets
1216	Significant components of deferred tax assets and liabilities [table]	Table	*	*	cstm:SignificantComponentsOfDeferredTaxAssetsAndLiabilitiesTable
1217	Maturity [axis]	Axis			ifrs-full:MaturityAxis
1218	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
1219	Expiring within 5 years [member]	Member			ifrs-full:LaterThanOneYearAndNotLaterThanFiveYearsMember
1220	Expiring after 5 years and limited [member]	Member			cstm:LaterThanFiveYearsAndLimitedMember
1221	Unlimited [member]	Member			cstm:UnlimitedMember
1222	Temporary difference, unused tax losses and unused tax credits [axis]	Axis			ifrs-full:TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis
1223	Temporary difference, unused tax losses and unused tax credits [member]	Member			ifrs-full:TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsMember
1224	Unused tax losses [member]	Member			ifrs-full:UnusedTaxLossesMember
1225	Long-term assets [member]	Member			cstm:LongTermAssetsMember
1226	Pensions [member]	Member			cstm:PensionsMember
1227	Other temporary differences [member]	Member			ifrs-full:OtherTemporaryDifferencesMember
1228	Temporary differences [member]	Member			ifrs-full:TemporaryDifferenceMember
1229	Significant components of deferred tax assets and liabilities [line items]	LineItems			cstm:SignificantComponentsOfDeferredTaxAssetsAndLiabilitiesLineItems
1230	Tax losses	Concept (Monetary)	As Of		ifrs-full:UnusedTaxLossesForWhichNoDeferredTaxAssetRecognised
1231	Deductible temporary differences	Concept (Monetary)	As Of		ifrs-full:DeductibleTemporaryDifferencesForWhichNoDeferredTaxAssetIsRecognised
1232	Total	Concept (Monetary)	As Of	Debit	cstm:NonRecognizedTaxAssets
1233	1130 - Disclosure - Trade Payables and Other - Detailed Information about Trade and Other Payables (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureTradePayablesAndOtherDetailedInformationAboutTradeAndOtherPayables
1234	Implied Table	Table	*	*	implied:Table
1235	Trade and other payables [abstract]	Abstract			ifrs-full:TradeAndOtherPayablesAbstract
1236	Trade payables	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentPayablesToTradeSuppliers
1237	Fixed assets payables	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentPayablesForPurchaseOfNoncurrentAssets
1238	Employees' entitlements	Concept (Monetary)	As Of	Credit	cstm:NoncurrentPayablesToEmployees
1239	Taxes payable other than income tax	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentPayablesOnSocialSecurityAndTaxesOtherThanIncomeTax
1240	Deferred revenue	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredIncomeClassifiedAsNoncurrent
1241	Contract liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentContractLiabilities
1242	Other payables	Concept (Monetary)	As Of	Credit	ifrs-full:OtherNoncurrentPayables
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1244	Total Trade payables and other	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentPayables
1245	Trade payables	Concept (Monetary)	As Of	Credit	ifrs-full:TradeAndOtherCurrentPayablesToTradeSuppliers
1246	Fixed assets payables	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentPayablesForPurchaseOfNoncurrentAssets
1247	Employees' entitlements	Concept (Monetary)	As Of	Credit	ifrs-full:ShorttermEmployeeBenefitsAccruals
1248	Taxes payable other than income tax	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentPayablesOnSocialSecurityAndTaxesOtherThanIncomeTax
1249	Deferred revenue	Concept (Monetary)	As Of	Credit	ifrs-full:DeferredIncomeClassifiedAsCurrent
1250	Contract liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentContractLiabilities
1251	Other payables	Concept (Monetary)	As Of	Credit	ifrs-full:OtherCurrentPayables
1252	Total Other	Concept (Monetary)	As Of	Credit	cstm:OtherCurrentPayablesOther
1253	Total Trade payables and other	Concept (Monetary)	As Of	Credit	ifrs-full:TradeAndOtherCurrentPayables
1254	1131 - Disclosure - Trade Payables and Other - Detailed information of contract liabilities (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureTradePayablesAndOtherDetailedInformationOfContractLiabilities
1255	Disclosure of disaggregation of revenue from contracts with customers [table]	Table	*	*	ifrs-full:DisclosureOfDisaggregationOfRevenueFromContractsWithCustomersTable
1256	Categories of assets recognised from costs to obtain or fulfil contracts with customers [axis]	Axis			ifrs-full:CategoriesOfAssetsRecognisedFromCostsToObtainOrFulfilContractsWithCustomersAxis
1257	Categories of assets recognised from costs to obtain or fulfil contracts with customers [member]	Member			ifrs-full:CategoriesOfAssetsRecognisedFromCostsToObtainOrFulfilContractsWithCustomersMember
1258	Deferred Tooling Revenue [member]	Member			cstm:DeferredToolingRevenueMember
1259	Advance Payment From Customers [member]	Member			cstm:AdvancePaymentFromCustomersMember
1260	Unrecognized Variable Consideration [member]	Member			cstm:UnrecognizedVariableConsiderationMember
1261	Other [member]	Member			cstm:OtherContractLiabilitiesMember
1262	Disclosure of disaggregation of contract liabilities with customers [line items]	LineItems			cstm:DisclosureOfDisaggregationOfContractLiabilitiesWithCustomersLineItems
1263	Non-current	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentContractLiabilities
1264	Current	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentContractLiabilities
1265	1132 - Disclosure - Trade Payables and Other - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureTradePayablesAndOtherAdditionalInformation
1266	Implied Table	Table	*	*	implied:Table
1267	Receivables from contracts with customers [abstract]	Abstract			ifrs-full:ReceivablesFromContractsWithCustomersAbstract
1268	Revenue recognized related to contract liabilities	Concept (Monetary)	For Period	Credit	cstm:RevenueRecognizedRelatedToContractLiabilities
1269	Deferred revenue related to contract liabilities	Concept (Monetary)	For Period	Credit	cstm:DeferredRevenueRelatedToContractLiabilities
1270	1133 - Disclosure - Borrowings - Summary of Borrowings (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureBorrowingsSummaryOfBorrowings
1271	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
1272	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
1273	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
1274	Constellium N.V. senior unsecured notes (Issued May 2014, due 2024) [member]	Member			cstm:ConstelliumNVSeniorUnsecuredNotesIssuedMayTwoThousandFourteenDueTwoThousandTwentyFourMember
1275	Constellium N.V. senior unsecured notes (Issued May 2014, due 2021) [member]	Member			cstm:ConstelliumNVSeniorUnsecuredNotesIssuedMayTwoThousandFourteenDueTwoThousandTwentyOneMember
1276	Constellium N.V. Senior Unsecured Notes (Issued February 2017, due 2025) [member]	Member			cstm:ConstelliumNvSeniorUnsecuredNotesIssuedFebruaryTwoThousandSeventeenDueTwoThousandTwentyFiveMember
1277	Constellium N.V. USD Senior Unsecured Notes (Issued November 2017, due 2026) [member]	Member			cstm:ConstelliumNvSeniorUnsecuredNotesIssuedNovemberTwoThousandSeventeenDueTwoThousandTwentySixMember
1278	Constellium N.V. EURO Senior Unsecured Notes (Issued November 2017, due 2026) [member]	Member			cstm:ConstelliumNvSeniorUnsecuredNotesIssuedNovemberTwoThousandSeventeenDueTwoThousandTwentySixOneMember
1279	Other loans [member]	Member			cstm:OtherLoansMember
1280	Pan US ABL facility (due 2022) [member]	Member			cstm:PanUsAblFacilityDueTwoThousandTwentyTwoMember
1281	Secured inventory based facility (due 2019) [member]	Member			cstm:SecuredInventoryBasedFacilityDueTwoThousandNineteenMember
1282	Unsecured revolving credit facilities (due 2021) [member]	Member			cstm:UnsecuredRevolvingCreditFacilitiesDueInTwoThousandTwentyOneMember
1283	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
1284	Nominal rate	Concept (Percent)	For Period		cstm:BorrowingsNominalInterestRate
1285	Nominal rate	Concept (Text/String)	For Period		cstm:DescriptionOfBorrowingsNominalInterestRate
1286	Effective rate	Concept (Percent)	As Of		ifrs-full:BorrowingsInterestRate
1287	Nominal value	Concept (Monetary)	As Of		ifrs-full:NotionalAmount
1288	Arrangement fees	Concept (Monetary)	As Of	Debit	cstm:BorrowingsArrangementFeesStepUp
1289	Accrued interest	Concept (Monetary)	As Of	Credit	cstm:AccruedInterest
1290	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
1291	Non-current	Concept (Monetary)	As Of	Credit	ifrs-full:LongtermBorrowings
1292	Current	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentBorrowingsAndCurrentPortionOfNoncurrentBorrowings
1293	1134 - Disclosure - Borrowings - Summary of Borrowings (Parenthetical) (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureBorrowingsSummaryOfBorrowingsParenthetical
1294	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
1295	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
1296	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
1297	BPI unsecured revolving credit facilities [member]	Member			cstm:BPIUnsecuredRevolvingCreditFacilitiesMember
1298	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
1299	Borrowing capacity	Concept (Monetary)	For Period	Debit	cstm:BorrowingCapacityUnderRevolvingCreditFacility
1300	1135 - Disclosure - Borrowings - Summary of Reconciliation of Movement in Net Borrowings Explanatory (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureBorrowingsSummaryOfReconciliationOfMovementInNetBorrowingsExplanatory
1301	Implied Table	Table	*	*	implied:Table
1302	Disclosure of detailed information about borrowings [abstract]	Abstract			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsAbstract
1303	Beginning Balance	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
1304	Proceeds from issuance of Senior Notes	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromIssueOfBondsNotesAndDebentures
1305	(Repayments) of Senior Notes	Concept (Monetary)	For Period	Credit	ifrs-full:RepaymentsOfBondsNotesAndDebentures
1306	(Repayments) / Proceeds from US Revolving Credit Facilities and other loans	Concept (Monetary)	For Period	Credit	ifrs-full:RepaymentsOfNoncurrentBorrowings
1307	Arrangement fees payment	Concept (Monetary)	As Of	Debit	cstm:ArrangementFeesPayment
1308	Finance lease repayment and others	Concept (Monetary)	For Period	Debit	cstm:RepaymentOfObligationsUnderFinanceLeasesAndOtherDebts
1309	Movement in interests accrued or capitalized	Concept (Monetary)	For Period	Credit	cstm:MovementInAccruedInterestAndInterestCostCapitalised
1310	New finance leases	Concept (Monetary)	For Period	Credit	cstm:FinanceLeases
1311	Deferred arrangement fees, step-up amortization and other	Concept (Monetary)	For Period	Credit	cstm:DeferredArrangementFeesStepupAmortizationAndOther
1312	Effects of changes in foreign exchange rates	Concept (Monetary)	For Period	Credit	cstm:BorrowingsEffectOfChangesInForeignExchangeRates
1313	Ending Balance	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
1314	1136 - Disclosure - Borrowings - Summary of Reconciliation of Movement in Net Borrowings Explanatory (Parenthetical) (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureBorrowingsSummaryOfReconciliationOfMovementInNetBorrowingsExplanatoryParenthetical
1315	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
1316	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
1317	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
1318	Constellium N.V. USD Senior Unsecured Notes (Issued November 2017, due 2026) [member]	Member			cstm:ConstelliumNvSeniorUnsecuredNotesIssuedNovemberTwoThousandSeventeenDueTwoThousandTwentySixMember
1319	Constellium N.V. Senior Unsecured Notes (Issued February 2017, due 2025) [member]	Member			cstm:ConstelliumNvSeniorUnsecuredNotesIssuedFebruaryTwoThousandSeventeenDueTwoThousandTwentyFiveMember
1320	Senior secured and unsecured notes [member]	Member			cstm:SeniorSecuredAndUnsecuredNotesMember
1321	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
1322	Proceeds from the issuance of senior notes	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromIssueOfBondsNotesAndDebentures
1323	Redemption of senior notes	Concept (Monetary)	For Period	Credit	ifrs-full:RepaymentsOfBondsNotesAndDebentures
1324	Exchange rate	Concept (Decimal)	As Of		ifrs-full:ClosingForeignExchangeRate
1325	1137 - Disclosure - Borrowings - Summary of Composition of Carrying Amounts of Total Borrowings (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureBorrowingsSummaryOfCompositionOfCarryingAmountsOfTotalBorrowings
1326	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
1327	Currency [Axis]	Axis			srt:CurrencyAxis
1328	All Currencies [Domain]	Member			currency:AllCurrenciesDomain
1329	U.S. Dollar [member]	Member			currency:USD
1330	Euro [member]	Member			currency:EUR
1331	Other currencies [member]	Member			cstm:OtherCurrenciesMember
1332	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
1333	Total borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
1334	1138 - Disclosure - Borrowings - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureBorrowingsAdditionalInformation
1335	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
1336	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
1337	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
1338	Pan US ABL facility (due 2022) [member]	Member			cstm:PanUsAblFacilityDueTwoThousandTwentyTwoMember
1339	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
1340	Debt covenant, Percentage of aggregate revolving loan commitments	Concept (Percent)	For Period		cstm:PercentageOfRevolvingLoanCommitments
1341	1139 - Disclosure - Financial Instruments - Summary of Financial Assets and Liabilities by Categories (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinancialInstrumentsSummaryOfFinancialAssetsAndLiabilitiesByCategories
1342	Disclosure of detailed information about financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfFinancialInstrumentsTable
1343	Categories of financial assets [axis]	Axis			ifrs-full:CategoriesOfFinancialAssetsAxis
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1345	At amortized cost [member]	Member			cstm:AtAmortizedCostMember
1346	At fair value through Profit and loss [member]	Member			ifrs-full:FinancialAssetsAtFairValueThroughProfitOrLossCategoryMember
1347	At fair value through OCI [member]	Member			ifrs-full:FinancialAssetsAtFairValueThroughOtherComprehensiveIncomeCategoryMember
1348	Loans and receivables [member]	Member			ifrs-full:LoansAndReceivablesCategoryMember
1349	Categories of financial liabilities [axis]	Axis			ifrs-full:CategoriesOfFinancialLiabilitiesAxis
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1352	At fair value through Profit and loss [member]	Member			ifrs-full:FinancialLiabilitiesAtFairValueThroughProfitOrLossCategoryMember
1353	At fair value through OCI [member]	Member			cstm:FinancialLiabilitiesMeasuredAtFairValueThroughOtherComprehensiveIncomeCategoryMember
1354	Disclosure of detailed information about financial instruments [line items]	LineItems			ifrs-full:DisclosureOfFinancialInstrumentsLineItems
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1356	Trade receivables	Concept (Monetary)	As Of	Debit	ifrs-full:TradeReceivables
1357	Finance lease receivables	Concept (Monetary)	As Of	Debit	ifrs-full:FinanceLeaseReceivables
1358	Other financial assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherFinancialAssets
1359	Total financial assets	Concept (Monetary)	As Of	Debit	ifrs-full:FinancialAssets
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1361	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:Borrowings
1362	Other financial liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:OtherFinancialLiabilities
1363	Total financial liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:FinancialLiabilities
1364	1140 - Disclosure - Financial Instruments - Summary of Other Financial Assets and Other Financial Liabilities Positions (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinancialInstrumentsSummaryOfOtherFinancialAssetsAndOtherFinancialLiabilitiesPositions
1365	Disclosure of detailed information about financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfFinancialInstrumentsTable
1366	Classes of financial assets [axis]	Axis			ifrs-full:ClassesOfFinancialAssetsAxis
1367	Financial assets, class [member]	Member			ifrs-full:FinancialAssetsMember
1368	Aluminium and premium future contract [member]	Member			cstm:AluminiumAndPremiumFutureContractMember
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1370	Currency commercial contracts [member]	Member			cstm:CurrencyCommercialContractsMember
1371	Currency net debt derivatives [member]	Member			cstm:CurrencyNetDebtDerivativesMember
1372	Margin call [member]	Member			cstm:MarginCallMember
1373	Net investment hedge [member]	Member			cstm:NetInvestmentHedgeMember
1374	Disclosure of detailed information about financial instruments [line items]	LineItems			ifrs-full:DisclosureOfFinancialInstrumentsLineItems
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1376	Current derivative financial assets	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentDerivativeFinancialAssets
1377	Derivatives assets	Concept (Monetary)	As Of	Debit	ifrs-full:DerivativeFinancialAssets
1378	Non-current loans	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentLoansAndReceivables
1379	Current loans	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentLoansAndReceivables
1380	Loans	Concept (Monetary)	As Of	Debit	ifrs-full:LoansAndReceivables
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1382	Other current financial assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherCurrentFinancialAssets
1383	Other financial assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherFinancialAssets
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1385	Other current financial liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:OtherCurrentFinancialLiabilities
1386	Other financial liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:OtherFinancialLiabilities
1387	Non-current derivative financial liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentDerivativeFinancialLiabilities
1388	Current derivative financial liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentDerivativeFinancialLiabilities
1389	Derivatives Liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:DerivativeFinancialLiabilities
1390	1141 - Disclosure - Financial Instruments - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinancialInstrumentsAdditionalInformation
1391	Disclosure of detailed information about financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfFinancialInstrumentsTable
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1395	Constellium N.V. Senior Unsecured Notes (Issued February 2017, due 2025) [member]	Member			cstm:ConstelliumNvSeniorUnsecuredNotesIssuedFebruaryTwoThousandSeventeenDueTwoThousandTwentyFiveMember
1396	Constellium N.V. EUR and USD Senior Unsecured Notes (Issued November 2017, due 2026) [member]	Member			cstm:ConstelliumNVEURAndUSDSeniorUnsecuredNotesIssuedNovemberTwoThousandSeventeenDueTwoThousandTwentySixMember
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1399	Fair value [member]	Member			ifrs-full:AtFairValueMember
1400	Disclosure of detailed information about financial instruments [line items]	LineItems			ifrs-full:DisclosureOfFinancialInstrumentsLineItems
1401	Percentage of fair value senior notes issued	Concept (Percent)	As Of		cstm:PercentageOfFairValueSeniorNotesIssued
1402	Senior Notes issued	Concept (Monetary)	As Of	Credit	cstm:SeniorNotesFairValue
1403	1142 - Disclosure - Financial Instruments - Summary of Derivatives Measured at Fair Value (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinancialInstrumentsSummaryOfDerivativesMeasuredAtFairValue
1404	Disclosure of financial instruments measured at fair value [table]	Table	*	*	cstm:DisclosureOfFinancialInstrumentsMeasuredAtFairValueTable
1405	Levels of fair value hierarchy [axis]	Axis			ifrs-full:LevelsOfFairValueHierarchyAxis
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1407	Level 1 of fair value hierarchy [member]	Member			ifrs-full:Level1OfFairValueHierarchyMember
1408	Level 2 of fair value hierarchy [member]	Member			ifrs-full:Level2OfFairValueHierarchyMember
1409	Disclosure of financial instruments measured at fair value [line items]	LineItems			cstm:DisclosureOfFinancialInstrumentsMeasuredAtFairValueLineItems
1410	Other financial assets-derivatives	Concept (Monetary)	As Of	Debit	ifrs-full:DerivativeFinancialAssets
1411	Other financial liabilities-derivatives	Concept (Monetary)	As Of	Credit	ifrs-full:DerivativeFinancialLiabilities
1412	1143 - Disclosure - Financial Risk Management - Summary of Nominal Value of Currency Derivatives (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinancialRiskManagementSummaryOfNominalValueOfCurrencyDerivatives
1413	Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [table]	Table	*	*	ifrs-full:DisclosureOfInformationAboutTermsAndConditionsOfHedgingInstrumentsAndHowTheyAffectFutureCashFlowsTable
1414	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1415	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1416	Currency risk [member]	Member			ifrs-full:CurrencyRiskMember
1417	Maturity [axis]	Axis			ifrs-full:MaturityAxis
1418	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
1419	Less than 1 year [member]	Member			ifrs-full:NotLaterThanOneYearMember
1420	Over 1 year [member]	Member			ifrs-full:LaterThanOneYearMember
1421	Hedging instruments [axis]	Axis			ifrs-full:HedgingInstrumentsAxis
1422	Hedging instruments [member]	Member			ifrs-full:HedgingInstrumentsMember
1423	Forward derivatives sales - USD/EUR [member]	Member			cstm:UsdEurForwardDerivativesSalesMember
1424	Forward derivatives sales - EUR/CHF [member]	Member			cstm:EurChfForwardDerivativesSalesMember
1425	Forward derivatives sales - Other currencies [member]	Member			cstm:OtherCurrenciesForwardDerivativesSalesMember
1426	Forward derivatives purchases - USD/EUR [member]	Member			cstm:UsdEurForwardDerivativesPurchasesMember
1427	Forward derivatives purchases - EUR/CHF [member]	Member			cstm:EurChfForwardDerivativesPurchasesMember
1428	Forward derivatives purchases - EUR/CZK [member]	Member			cstm:ForwardDerivativesPurchasesEurCzkMember
1429	Forward derivatives purchases - Other currencies [member]	Member			cstm:OtherCurrenciesForwardDerivativesPurchasesMember
1430	Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]	LineItems			ifrs-full:DisclosureOfInformationAboutTermsAndConditionsOfHedgingInstrumentsAndHowTheyAffectFutureCashFlowsLineItems
1431	Maturity period	Concept (Text/String)	For Period		cstm:DerivativeInstrumentMaturityPeriod
1432	Nominal value	Concept (Decimal)	As Of		ifrs-full:NominalAmountOfHedgingInstrument
1433	1144 - Disclosure - Financial Risk Management - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinancialRiskManagementAdditionalInformation
1434	Disclosure of credit risk exposure [table]	Table	*	*	ifrs-full:DisclosureOfCreditRiskExposureTable
1435	Range [axis]	Axis			ifrs-full:RangeAxis
1436	Ranges [member]	Member			ifrs-full:RangesMember
1437	Top of range [member]	Member			ifrs-full:TopOfRangeMember
1438	Bottom of range [member]	Member			ifrs-full:BottomOfRangeMember
1439	Sensitivity Analysis [axis]	Axis			cstm:SensitivityAnalysisAxis
1440	Sensitivity Analysis [domain]	Member			cstm:SensitivityAnalysisDomain
1441	50 basis point increase or decrease in the LIBOR or EURIBOR interest rates [member]	Member			cstm:FiftyBasisPointIncreaseOrDecreaseInTheLiborOrEuriborInterestRatesMember
1442	10% increase or decrease in the market price [member]	Member			cstm:TenPercentageIncreaseOrDecreaseInTheMarketPriceMember
1443	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1444	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1445	Commodity price risk [member]	Member			ifrs-full:CommodityPriceRiskMember
1446	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
1447	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
1448	Pan US ABL facility (due 2022) [member]	Member			cstm:PanUsAblFacilityDueTwoThousandTwentyTwoMember
1449	French inventory facility [member]	Member			cstm:FrenchInventoryFacilityMember
1450	Financial instruments measured at fair value through profit or loss because credit derivative is used to manage credit risk [axis]	Axis			ifrs-full:FinancialInstrumentsMeasuredAtFairValueThroughProfitOrLossBecauseCreditDerivativeIsUsedToManageCreditRiskAxis
1451	Financial instruments measured at fair value through profit or loss because credit derivative is used to manage credit risk [member]	Member			ifrs-full:FinancialInstrumentsMeasuredAtFairValueThroughProfitOrLossBecauseCreditDerivativeIsUsedToManageCreditRiskMember
1452	Forward purchase contracts versus EURO [member]	Member			cstm:ForwardPurchaseContractsVersusEuroMember
1453	Forward purchase contracts [member]	Member			cstm:ForwardPurchaseContractsMember
1454	Forward sale contracts [member]	Member			cstm:ForwardSaleContractsMember
1455	Hedging instruments [axis]	Axis			ifrs-full:HedgingInstrumentsAxis
1456	Hedging instruments [member]	Member			ifrs-full:HedgingInstrumentsMember
1457	Derivative classified as cash flow hedge [member]	Member			cstm:DerivativeClassifiedAsCashFlowHedgeMember
1458	Cross currency swaps [member]	Member			cstm:CrossCurrencySwapsMember
1459	Aluminium [member]	Member			cstm:AluminiumMember
1460	Classes of financial assets [axis]	Axis			ifrs-full:ClassesOfFinancialAssetsAxis
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1462	Foreign exchange forward contracts [member]	Member			cstm:ForeignExchangeForwardContractsMember
1463	Forward contract [member]	Member			ifrs-full:ForwardContractMember
1464	Disclosure of liquidity risk [line items]	LineItems			cstm:DisclosureOfLiquidityRiskLineItems
1465	Nominal amount hedging instrument	Concept (Monetary)	As Of	Credit	cstm:FullNominalAmountOfHedgingInstrument
1466	Maturity period	Concept (Year)	For Period		cstm:DerivativeInstrumentMaturityDate
1467	Net position hedges related to loans and deposits	Concept (Monetary)	For Period	Credit	cstm:NetPositionHedgesRelatedToLoansAndDeposits
1468	Total nominal amount forward contracts	Concept (Monetary)	As Of	Credit	cstm:NominalAmountOfHedgingInstruments
1469	Unrealized gain / loss of the net investment hedge	Concept (Monetary)	For Period	Credit	cstm:UnrealizedGainLossOfNetInvestmentHedge
1470	Impact of increase or decrease in market price in gain or loss from derivatives	Concept (Monetary)	For Period	Debit	cstm:ImpactOfIncreaseOrDecreaseInMarketPriceInGainOrLossFromDerivatives
1471	Margin requirement for aluminum and other commodity hedges	Concept (Monetary)	As Of	Debit	cstm:MarginRequirementForAluminumAndOtherCommodityHedges
1472	Impact of increase or decrease in interest rate in income before income tax	Concept (Monetary)	For Period	Credit	cstm:ImpactOfIncreaseOrDecreaseInInterestRateInIncomeLossBeforeIncomeTax
1473	Percentage of trade account receivables insured	Concept (Percent)	As Of		cstm:PercentageOfTradeAccountReceivablesInsured
1474	Borrowing base	Concept (Monetary)	As Of	Credit	cstm:BorrowingFacility
1475	Liquidity value	Concept (Monetary)	As Of	Debit	ifrs-full:FinancialAssetsHeldForManagingLiquidityRisk
1476	Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
1477	Undrawn facilities	Concept (Monetary)	As Of	Credit	ifrs-full:UndrawnBorrowingFacilities
1478	Revolving credit facilities outstanding	Concept (Monetary)	As Of	Credit	cstm:RevolvingCreditFacilityOutstanding
1479	1145 - Disclosure - Financial Risk Management - Summary of Effect of Foreign Currency Derivatives Impacts and Commercial Transactions Exposures (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinancialRiskManagementSummaryOfEffectOfForeignCurrencyDerivativesImpactsAndCommercialTransactionsExposures
1480	Disclosure of nature and extent of risks arising from financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsTable
1481	Derivative Instrument [axis]	Axis			cstm:DerivativeInstrumentAxis
1482	Derivative Instrument [domain]	Member			cstm:DerivativeInstrumentDomain
1483	Derivatives that do not qualify for hedge accounting [member]	Member			cstm:NonqualifyingHedgesMember
1484	Derivatives that qualify for hedge accounting [member]	Member			cstm:QualifyingHedgesMember
1485	Consolidated and separate financial statements [axis]	Axis			ifrs-full:ConsolidatedAndSeparateFinancialStatementsAxis
1486	Consolidated [member]	Member			ifrs-full:ConsolidatedMember
1487	Other gains and losses [member]	Member			cstm:OtherGainsAndLossesMember
1488	Revenue [member]	Member			cstm:RevenueMember
1489	Other comprehensive income (loss) [member]	Member			cstm:OtherComprehensiveIncomeLossMember
1490	Disclosure of nature and extent of risks arising from financial instruments [line items]	LineItems			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
1491	Realized gains / (losses) on foreign currency derivatives - net	Concept (Monetary)	For Period	Credit	cstm:RealizedGainsLossesOnForeignCurrencyDerivativesNet
1492	Included in Unrealized (losses) / gains on foreign currency derivatives - net	Concept (Monetary)	For Period	Credit	cstm:UnrealizedGainsLossesOnForeignCurrencyDerivativesNet
1493	Realized gains / (losses) in ineffective portion of derivatives	Concept (Monetary)	For Period	Credit	cstm:RealizedGainLossInIneffectivePortionOfDerivatives
1494	(Losses) reclassified from cash flow hedge reserve to Consolidated Income Statement	Concept (Monetary)	For Period	Credit	cstm:GainsLossesRecognizedOnReclassificationAdjustmentsOnCashFlowHedges
1495	1146 - Disclosure - Financial Risk Management - Summary of Effect of Foreign Currency Derivatives Impacts and Financing Transaction Exposures (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinancialRiskManagementSummaryOfEffectOfForeignCurrencyDerivativesImpactsAndFinancingTransactionExposures
1496	Disclosure of nature and extent of risks arising from financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsTable
1497	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1498	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1499	Currency risk [member]	Member			ifrs-full:CurrencyRiskMember
1500	Consolidated and separate financial statements [axis]	Axis			ifrs-full:ConsolidatedAndSeparateFinancialStatementsAxis
1501	Consolidated [member]	Member			ifrs-full:ConsolidatedMember
1502	Finance costs [member]	Member			cstm:FinanceCostsMember
1503	Disclosure of nature and extent of risks arising from financial instruments [line items]	LineItems			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
1504	Realized gains / (losses) on foreign currency derivatives-net	Concept (Monetary)	For Period	Credit	cstm:RealizedGainsLossesOnForeignCurrencyDerivativesNet
1505	Unrealized gains / (losses) on foreign currency derivatives-net	Concept (Monetary)	For Period	Credit	cstm:UnrealizedGainsLossesOnForeignCurrencyDerivativesNet
1506	Total	Concept (Monetary)	For Period	Credit	ifrs-full:GainsLossesOnChangeInFairValueOfDerivatives
1507	1147 - Disclosure - Financial Risk Management - Summary of Impact on Profit and Equity (Before Tax Effect) of a 10 % Strengthening of US Dollar Versus Euro for Non US Dollar Functional Currency Entities (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinancialRiskManagementSummaryOfImpactOnProfitAndEquityBeforeTaxEffectOfA10StrengtheningOfUSDollarVersusEuroForNonUSDollarFunctionalCurrencyEntities
1508	Disclosure of nature and extent of risks arising from financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsTable
1509	Classes of financial instruments [axis]	Axis			ifrs-full:ClassesOfFinancialInstrumentsAxis
1510	Financial instruments, class [member]	Member			ifrs-full:ClassesOfFinancialInstrumentsMember
1511	Derivatives on commercial transaction [member]	Member			cstm:DerivativesOnCommercialTransactionMember
1512	Trade receivables [member]	Member			ifrs-full:TradeReceivablesMember
1513	Trade payables [member]	Member			cstm:TradePayablesMember
1514	Cash in Bank and intercompany loans [member]	Member			cstm:CashInBankAndIntercompanyLoansMember
1515	Borrowings [member]	Member			cstm:Borrowings1Member
1516	Derivatives on financing transaction [member]	Member			cstm:DerivativesOnFinancingTransactionMember
1517	Sensitivity Analysis [axis]	Axis			cstm:SensitivityAnalysisAxis
1518	Sensitivity Analysis [domain]	Member			cstm:SensitivityAnalysisDomain
1519	10% strengthening US Dollar/Euro [member]	Member			cstm:TenPercentageStrengtheningUsDollarEuroMember
1520	Types of hedges [axis]	Axis			ifrs-full:TypesOfHedgesAxis
1521	Hedges [member]	Member			ifrs-full:TypesOfHedgesMember
1522	Commercial transaction exposure [member]	Member			cstm:CommercialTransactionExposureMember
1523	Disclosure of nature and extent of risks arising from financial instruments [line items]	LineItems			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
1524	Effect on profit before tax	Concept (Monetary)	For Period	Credit	cstm:ForeignExchangeSensitivityOnCommercialAndFinancingTransactionsExposuresEffectOnProfitBeforeTax
1525	Effect on pretax equity	Concept (Monetary)	For Period	Credit	cstm:ForeignExchangeSensitivityOnCommercialAndFinancingTransactionsExposuresEffectOnPretaxEquity
1526	1148 - Disclosure - Financial Risk Management - Summary of Impact on Profit and Equity (Before Tax Effect) of a 10 % Strengthening of US Dollar Versus Euro for Non US Dollar Functional Currency Entities (Parenthetical) (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinancialRiskManagementSummaryOfImpactOnProfitAndEquityBeforeTaxEffectOfA10StrengtheningOfUSDollarVersusEuroForNonUSDollarFunctionalCurrencyEntitiesParenthetical
1527	Disclosure of nature and extent of risks arising from financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsTable
1528	Classes of financial instruments [axis]	Axis			ifrs-full:ClassesOfFinancialInstrumentsAxis
1529	Financial instruments, class [member]	Member			ifrs-full:ClassesOfFinancialInstrumentsMember
1530	Derivatives on commercial transaction [member]	Member			cstm:DerivativesOnCommercialTransactionMember
1531	Disclosure of nature and extent of risks arising from financial instruments [line items]	LineItems			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
1532	Effect on pretax equity	Concept (Monetary)	For Period	Credit	cstm:ForeignExchangeSensitivityOnCommercialAndFinancingTransactionsExposuresEffectOnPretaxEquity
1533	1149 - Disclosure - Financial Risk Management - Summary of Impact on Profit and Equity (before tax effect) of a 10 % strengthening of the US Dollar versus the Euro for US Dollar functional currency (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinancialRiskManagementSummaryOfImpactOnProfitAndEquitybeforeTaxEffectOfA10StrengtheningOfTheUSDollarVersusTheEuroForUSDollarFunctionalCurrency
1534	Disclosure of nature and extent of risks arising from financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsTable
1535	Sensitivity Analysis [axis]	Axis			cstm:SensitivityAnalysisAxis
1536	Sensitivity Analysis [domain]	Member			cstm:SensitivityAnalysisDomain
1537	10% strengthening US Dollar/Euro [member]	Member			cstm:TenPercentageStrengtheningUsDollarEuroMember
1538	Disclosure of nature and extent of risks arising from financial instruments [line items]	LineItems			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
1539	Effect on profit before tax	Concept (Monetary)	For Period	Credit	cstm:ForeignExchangeSensitivityEffectOnProfitBeforeTax
1540	Effect on pretax equity	Concept (Monetary)	For Period	Credit	cstm:ForeignExchangeSensitivityEffectOnPretaxEquity
1541	1150 - Disclosure - Financial Risk Management - Summary of Nominal Value of Commodity Derivatives (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinancialRiskManagementSummaryOfNominalValueOfCommodityDerivatives
1542	Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [table]	Table	*	*	ifrs-full:DisclosureOfInformationAboutTermsAndConditionsOfHedgingInstrumentsAndHowTheyAffectFutureCashFlowsTable
1543	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1544	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1545	Commodity price risk [member]	Member			ifrs-full:CommodityPriceRiskMember
1546	Maturity [axis]	Axis			ifrs-full:MaturityAxis
1547	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
1548	Less than 1 year [member]	Member			ifrs-full:NotLaterThanOneYearMember
1549	Over 1 year [member]	Member			ifrs-full:LaterThanOneYearMember
1550	Hedging instruments [axis]	Axis			ifrs-full:HedgingInstrumentsAxis
1551	Hedging instruments [member]	Member			ifrs-full:HedgingInstrumentsMember
1552	Aluminium [member]	Member			cstm:AluminiumMember
1553	Premiums [member]	Member			cstm:PremiumsMember
1554	Copper [member]	Member			cstm:CopperMember
1555	Silver [member]	Member			cstm:SilverMember
1556	Zinc [member]	Member			cstm:ZincMember
1557	Natural gas [member]	Member			cstm:NaturalGasMember
1558	Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]	LineItems			ifrs-full:DisclosureOfInformationAboutTermsAndConditionsOfHedgingInstrumentsAndHowTheyAffectFutureCashFlowsLineItems
1559	Maturity period	Concept (Text/String)	For Period		cstm:DerivativeInstrumentMaturityPeriod
1560	Nominal amount of derivatives	Concept (Monetary)	As Of		ifrs-full:CreditDerivativeNominalAmount
1561	1151 - Disclosure - Financial Risk Management - Summary of Mark-to-market movements Recognized in Other Gains (Losses) - Net (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinancialRiskManagementSummaryOfMarktomarketMovementsRecognizedInOtherGainsLossesNet
1562	Disclosure of nature and extent of risks arising from financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsTable
1563	Types of risks [axis]	Axis			ifrs-full:TypesOfRisksAxis
1564	Risks [member]	Member			ifrs-full:TypesOfRisksMember
1565	Commodity price risk [member]	Member			ifrs-full:CommodityPriceRiskMember
1566	Disclosure of nature and extent of risks arising from financial instruments [line items]	LineItems			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
1567	Realized gain / (loss) on commodity derivatives-net	Concept (Monetary)	For Period	Credit	cstm:RealizedGainsLossesOnCommodityDerivativesNet
1568	Unrealized (loss) / gain on commodity derivatives-net	Concept (Monetary)	For Period	Credit	cstm:UnrealizedGainsLossesOnCommodityDerivativesNet
1569	1152 - Disclosure - Financial Risk Management - Summary of Exposure to Financial Counterparties by Rating Type (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureFinancialRiskManagementSummaryOfExposureToFinancialCounterpartiesByRatingType
1570	Disclosure of nature and extent of risks arising from financial instruments [table]	Table	*	*	ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsTable
1571	External credit grades [axis]	Axis			ifrs-full:ExternalCreditGradesAxis
1572	Entity's total for external credit grades [member]	Member			ifrs-full:EntitysTotalForExternalCreditGradesMember
1573	Rated Aa or better [member]	Member			cstm:RatedAaOrBetterMember
1574	Rated A [member]	Member			cstm:RatedAMember
1575	Rated Baa [member]	Member			cstm:RatedBaaMember
1576	Disclosure of nature and extent of risks arising from financial instruments [line items]	LineItems			ifrs-full:DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
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1807	1169 - Disclosure - Share Capital - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureShareCapitalAdditionalInformation
1808	Implied Table	Table	*	*	implied:Table
1809	Disclosure of classes of share capital [abstract]	Abstract			ifrs-full:DisclosureOfClassesOfShareCapitalAbstract
1810	Authorized share capital	Concept (Monetary)	As Of	Credit	cstm:AuthorisedCapital
1811	Number of share authorized	Concept (Shares)	As Of		ifrs-full:NumberOfSharesAuthorised
1812	Nominal value of per shares	Concept (Share)	As Of		ifrs-full:ParValuePerShare
1813	1170 - Disclosure - Share Capital - Schedule of Share Capital (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureShareCapitalScheduleOfShareCapital
1814	Disclosure of classes of share capital [table]	Table	*	*	ifrs-full:DisclosureOfClassesOfShareCapitalTable
1815	Components of equity [axis]	Axis			ifrs-full:ComponentsOfEquityAxis
1816	Equity [member]	Member			ifrs-full:EquityMember
1817	Share capital [member]	Member			ifrs-full:IssuedCapitalMember
1818	Share premium [member]	Member			ifrs-full:SharePremiumMember
1819	Disclosure of classes of share capital [line items]	LineItems			ifrs-full:DisclosureOfClassesOfShareCapitalLineItems
1820	Beginning balance	Concept (Shares)	As Of		ifrs-full:NumberOfSharesOutstanding
1821	New shares issued	Concept (Shares)	For Period		ifrs-full:IncreaseDecreaseInNumberOfOrdinarySharesIssued
1822	Ending balance	Concept (Shares)	As Of		ifrs-full:NumberOfSharesOutstanding
1823	Beginning balance	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
1824	New shares issued	Concept (Monetary)	For Period	Credit	ifrs-full:IssueOfEquity
1825	Ending balance	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
1826	1171 - Disclosure - Share Capital - Schedule of Share Capital (Parenthetical) (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureShareCapitalScheduleOfShareCapitalParenthetical
1827	Disclosure of classes of share capital [table]	Table	*	*	ifrs-full:DisclosureOfClassesOfShareCapitalTable
1828	Classes of share capital [axis]	Axis			ifrs-full:ClassesOfShareCapitalAxis
1829	Share capital [member]	Member			ifrs-full:ClassesOfShareCapitalMember
1830	Common shares [member]	Member			cstm:CommonSharesMember
1831	Ordinary shares [member]	Member			ifrs-full:OrdinarySharesMember
1832	Defined benefit plans [axis]	Axis			ifrs-full:DefinedBenefitPlansAxis
1833	Defined benefit plans [member]	Member			ifrs-full:DefinedBenefitPlansMember
1834	Employees [member]	Member			cstm:EmployeesMember
1835	Disclosure of classes of share capital [line items]	LineItems			ifrs-full:DisclosureOfClassesOfShareCapitalLineItems
1836	Share issued	Concept (Shares)	For Period		ifrs-full:IncreaseDecreaseInNumberOfOrdinarySharesIssued
1837	Treasury shares held	Concept (Shares)	As Of		cstm:NumberOfSharesIssuedAndGranted
1838	1172 - Disclosure - Commitments - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureCommitmentsAdditionalInformation
1839	Implied Table	Table	*	*	implied:Table
1840	Disclosure of operating lease [abstract]	Abstract			cstm:DisclosureOfOperatingLeaseAbstract
1841	Rent expense	Concept (Monetary)	For Period	Debit	ifrs-full:RentalExpense
1842	1173 - Disclosure - Commitments - Non Cancellable Operating Leases Commitments (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureCommitmentsNonCancellableOperatingLeasesCommitments
1843	Disclosure Of Non-cancellable Operating Leases Commitments [table]	Table	*	*	cstm:DisclosureOfNoncancellableOperatingLeasesCommitmentsTable
1844	Maturity [axis]	Axis			ifrs-full:MaturityAxis
1845	Aggregated time bands [member]	Member			ifrs-full:AggregatedTimeBandsMember
1846	Less than 1 year [member]	Member			ifrs-full:NotLaterThanOneYearMember
1847	Expiring within 5 years [member]	Member			ifrs-full:LaterThanOneYearAndNotLaterThanFiveYearsMember
1848	More than 5 years [member]	Member			ifrs-full:LaterThanFiveYearsMember
1849	Disclosure of non-cancellable operating leases commitments [line items]	LineItems			cstm:DisclosureOfNoncancellableOperatingLeasesCommitmentsLineItems
1850	Minimum lease payments	Concept (Monetary)	As Of	Credit	ifrs-full:MinimumLeasePaymentsPayableUnderNoncancellableOperatingLease
1851	1174 - Disclosure - Commitments - Capital Expenditures Commitments (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureCommitmentsCapitalExpendituresCommitments
1852	Disclosure Of Capital Expenditures Commitments [table]	Table	*	*	cstm:DisclosureOfCapitalExpendituresCommitmentsTable
1853	Classes of assets [axis]	Axis			ifrs-full:ClassesOfAssetsAxis
1854	Assets [member]	Member			ifrs-full:ClassesOfAssetsMember
1855	Property, plant and equipment [member]	Member			ifrs-full:PropertyPlantAndEquipmentMember
1856	Classes of intangible assets other than goodwill [axis]	Axis			ifrs-full:ClassesOfIntangibleAssetsOtherThanGoodwillAxis
1857	Intangible assets other than goodwill [member]	Member			ifrs-full:IntangibleAssetsOtherThanGoodwillMember
1858	Computer software [member]	Member			ifrs-full:ComputerSoftwareMember
1859	Disclosure of capital expenditures commitments [line items]	LineItems			cstm:DisclosureOfCapitalExpendituresCommitmentsLineItems
1860	Capital expenditure commitments	Concept (Monetary)	As Of	Credit	ifrs-full:CapitalCommitments
1861	1175 - Disclosure - Related Parties - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureRelatedPartiesAdditionalInformation
1862	Disclosure of detailed information about borrowings [table]	Table	*	*	ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsTable
1863	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
1864	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
1865	BPI unsecured revolving credit facilities [member]	Member			cstm:BPIUnsecuredRevolvingCreditFacilitiesMember
1866	Disclosure of detailed information about borrowings [line items]	LineItems			ifrs-full:DisclosureOfDetailedInformationAboutBorrowingsLineItems
1867	Borrowing capacity	Concept (Monetary)	For Period	Debit	cstm:BorrowingCapacityUnderRevolvingCreditFacility
1868	1176 - Disclosure - Related Parties - Summary of Key Management Personnel Compensation (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureRelatedPartiesSummaryOfKeyManagementPersonnelCompensation
1869	Implied Table	Table	*	*	implied:Table
1870	Disclosure of transactions between related parties [abstract]	Abstract			ifrs-full:DisclosureOfTransactionsBetweenRelatedPartiesAbstract
1871	Short term employee benefits	Concept (Monetary)	For Period	Debit	ifrs-full:KeyManagementPersonnelCompensationShorttermEmployeeBenefits
1872	Directors' fees	Concept (Monetary)	For Period	Debit	ifrs-full:DirectorsRemunerationExpense
1873	Share-based compensation	Concept (Monetary)	For Period	Debit	ifrs-full:KeyManagementPersonnelCompensationSharebasedPayment
1874	Post-employments benefits	Concept (Monetary)	For Period	Debit	ifrs-full:KeyManagementPersonnelCompensationPostemploymentBenefits
1875	Termination benefits	Concept (Monetary)	For Period	Debit	ifrs-full:KeyManagementPersonnelCompensationTerminationBenefits
1876	Employer social contribution	Concept (Monetary)	For Period	Debit	cstm:KeyManagementPersonnelCompensationEmployerSocialContribution
1877	Total	Concept (Monetary)	For Period	Debit	ifrs-full:KeyManagementPersonnelCompensation
1878	1177 - Disclosure - Share-Based Compensation - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureShareBasedCompensationAdditionalInformation
1879	Share Based Payment Plans [table]	Table	*	*	cstm:ShareBasedPaymentPlansTable
1880	Types of share-based payment arrangements [axis]	Axis			ifrs-full:TypesOfSharebasedPaymentArrangementsAxis
1881	Share-based payment arrangements [member]	Member			ifrs-full:SharebasedPaymentArrangementsMember
1882	Restricted Stock Units [member]	Member			cstm:RestrictedStockUnitsMember
1883	Equity Awards Plans [member]	Member			cstm:EquityAwardsPlanMember
1884	Performance share units (PSUs) [member]	Member			cstm:PerformanceShareUnitsMember
1885	PSUs granted in 2015 and 2016 [member]	Member			cstm:PerformanceShareUnitsGrantedInTwoThousandAndFifteenAndTwoThousandAndSixteenMember
1886	PSUs granted in 2017 and 2018 [member]	Member			cstm:PerformanceShareUnitsGrantedInTwoThousandAndSeventeenAndTwoThousandAndEighteenMember
1887	PSUs granted in November 2015 [member]	Member			cstm:PerformanceShareUnitsGrantedInNovemberTwoThousandAndFifteenMember
1888	PSUs granted in March 2016 [member]	Member			cstm:PerformanceShareUnitsGrantedInMarchTwoThousandAndSixteenMember
1889	PSUs granted in May 2016 [member]	Member			cstm:PerformanceShareUnitsGrantedInMayTwoThousandAndSixteenMember
1890	PSUs granted in August 2016 [member]	Member			cstm:PerformanceShareUnitsGrantedInAugustTwoThousandAndSixteenMember
1891	PSUs granted in November 2016 [member]	Member			cstm:PerformanceShareUnitsGrantedInNovemberTwoThousandAndSixteenMember
1892	PSUs granted in 2016 [member]	Member			cstm:PerformanceShareUnitsGrantedInTwoThousandAndSixteenMember
1893	Range [axis]	Axis			ifrs-full:RangeAxis
1894	Ranges [member]	Member			ifrs-full:RangesMember
1895	Bottom of range [member]	Member			ifrs-full:BottomOfRangeMember
1896	Top of range [member]	Member			ifrs-full:TopOfRangeMember
1897	Share Based Payment Plans [line items]	LineItems			cstm:ShareBasedPaymentPlansLineItems
1898	Share based compensation, vesting period	Concept (xbrli:durationItemType)	For Period		cstm:ShareBasedCompensationVestingPeriod
1899	Percentage of vesting multiplier	Concept (Percent)	For Period		cstm:PercentageOfSharebasedPaymentsVestingMultiplier
1900	Share based compensation, measurement period	Concept (xbrli:durationItemType)	For Period		cstm:ShareBasedCompensationMeasurementPeriod
1901	Percentage of vesting	Concept (Percent)	For Period		cstm:PercentageOfSharebasedPaymentsVesting
1902	Total Stockholders return percentage achieved	Concept (Percent)	For Period		cstm:SharebasedCompensationStockholdersReturnPercentage
1903	Potential additional shares to be vested	Concept (Shares)	For Period		cstm:PotentialAdditionalSharesToBeVested
1904	Vesting date of additional shares	Concept (Text/String)	For Period		ifrs-full:DescriptionOfMaximumTermOfOptionsGrantedForSharebasedPaymentArrangement
1905	Number of shares granted	Concept (Decimal)	For Period		cstm:NumberOfSharesInOtherEquityInstrumentsGrantedInSharebasedPaymentArrangement
1906	Vesting period on the grant date	Concept (xbrli:durationItemType)	For Period		cstm:ShareBasedPaymentArrangementVestingPeriod
1907	Description of vesting requirements for share-based payment arrangement	Concept (Text/String)	For Period		ifrs-full:DescriptionOfVestingRequirementsForSharebasedPaymentArrangement
1908	Number of RSU vested	Concept (Decimal)	As Of		cstm:NumberOfOtherEquityInstrumentsVestedInSharebasedPaymentArrangement
1909	Total expense related to the potential ordinary shares	Concept (Monetary)	For Period	Debit	ifrs-full:ExpenseFromSharebasedPaymentTransactionsWithEmployees
1910	1178 - Disclosure - Share-Based Compensation - Summary of Performance-Based RSU (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureShareBasedCompensationSummaryOfPerformanceBasedRSU
1911	Disclosure Of Input Of Model Used For Performance-Based RSU [table]	Table	*	*	cstm:DisclosureOfInputOfModelUsedForPerformancebasedRSUTable
1912	Types of share-based payment arrangements [axis]	Axis			ifrs-full:TypesOfSharebasedPaymentArrangementsAxis
1913	Share-based payment arrangements [member]	Member			ifrs-full:SharebasedPaymentArrangementsMember
1914	2018 performance shares [member]	Member			cstm:TwoThousandAndEighteenPerformanceSharesMember
1915	Disclosure of Input of Model Used for Performance-Based RSU [Line Items]	LineItems			cstm:DisclosureOfInputOfModelUsedForPerformancebasedRSULineItems
1916	Fair value at grant date (in euros)	Concept (Share)	For Period		cstm:FairValueAtMeasurementDateOtherEquityInstrumentsGrantedPerShare
1917	Share price at grant date (in euros)	Concept (Monetary)	For Period		cstm:SharePriceAtGrantedDate
1918	Dividend yield	Concept (Percent)	For Period		cstm:ExpectedDividendAsPercentageOtherEquityInstrumentsGranted
1919	Expected volatility	Concept (Percent)	For Period		cstm:ExpectedVolatilityOtherEquityInstrumentsGranted
1920	Risk-free interest rate (US government bond yield)	Concept (Percent)	For Period		cstm:RiskFreeInterestRateOtherEquityInstrumentsGranted
1921	Model used	Concept (Text/String)	For Period		ifrs-full:DescriptionOfOptionPricingModelShareOptionsGranted
1922	1179 - Disclosure - Share-Based Compensation - Summary of Movements in Shares (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureShareBasedCompensationSummaryOfMovementsInShares
1923	Disclosure Of Movement Of Potential Shares [table]	Table	*	*	cstm:DisclosureOfMovementOfPotentialSharesTable
1924	Types of share-based payment arrangements [axis]	Axis			ifrs-full:TypesOfSharebasedPaymentArrangementsAxis
1925	Share-based payment arrangements [member]	Member			ifrs-full:SharebasedPaymentArrangementsMember
1926	Performance-Based RSU [member]	Member			cstm:PerformanceBasedRestrictedStockUnitsMember
1927	Restricted Stock Units [member]	Member			cstm:RestrictedStockUnitsMember
1928	Equity Awards Plans [member]	Member			cstm:EquityAwardsPlanMember
1929	Disclosure of movement of potential shares [line items]	LineItems			cstm:DisclosureOfMovementOfPotentialSharesLineItems
1930	Potential Shares, Beginning balance	Concept (Decimal)	As Of		ifrs-full:NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement
1931	Potential Shares, Granted	Concept (Decimal)	For Period		ifrs-full:NumberOfInstrumentsOtherEquityInstrumentsGranted
1932	Potential Shares, Over performance	Concept (Decimal)	For Period		cstm:NumberOfInstrumentsOtherEquityInstrumentsOverPerformance
1933	Potential Shares, Vested	Concept (Shares)	For Period		cstm:NumberOfInstrumentsOtherEquityInstrumentsVested
1934	Potential Shares, Forfeited	Concept (Decimal)	For Period		ifrs-full:NumberOfOtherEquityInstrumentsForfeitedInSharebasedPaymentArrangement
1935	Potential Shares, Ending balance	Concept (Decimal)	As Of		ifrs-full:NumberOfOtherEquityInstrumentsOutstandingInSharebasedPaymentArrangement
1936	Weighted- Average Grant-Date Fair Value per Share, Beginning balance	Concept (Monetary)	As Of		cstm:WeightedAverageFairValueOnMeasurementDateOtherEquityInstrumentsGrantedPerShare
1937	Weighted- Average Grant-Date Fair Value per Share, Granted	Concept (Monetary)	For Period		cstm:WeightedAverageGrantDateFairValuePerShareOtherEquityInstrumentsGranted
1938	Weighted- Average Grant-Date Fair Value per Share, Over performance	Concept (Monetary)	For Period		cstm:WeightedAverageGrantDateFairValuePerShareOtherEquityInstrumentsOverPerformance
1939	Weighted- Average Grant-Date Fair Value per Share, Vested	Concept (Monetary)	For Period		cstm:WeightedAverageGrantDateFairValuePerShareOtherEquityInstrumentsVested
1940	Weighted- Average Grant-Date Fair Value per Share, Forfeited	Concept (Monetary)	For Period		cstm:WeightedAverageGrantDateFairValuePerShareOtherEquityInstrumentsForfeited
1941	Weighted- Average Grant-Date Fair Value per Share, Ending balance	Concept (Monetary)	As Of		cstm:WeightedAverageFairValueOnMeasurementDateOtherEquityInstrumentsGrantedPerShare
1942	1180 - Disclosure - Share-Based Compensation - Summary of Movements in Shares (Parenthetical) (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureShareBasedCompensationSummaryOfMovementsInSharesParenthetical
1943	Disclosure Of Movement Of Potential Shares [table]	Table	*	*	cstm:DisclosureOfMovementOfPotentialSharesTable
1944	Types of share-based payment arrangements [axis]	Axis			ifrs-full:TypesOfSharebasedPaymentArrangementsAxis
1945	Share-based payment arrangements [member]	Member			ifrs-full:SharebasedPaymentArrangementsMember
1946	Performance share units (PSUs) [member]	Member			cstm:PerformanceShareUnitsMember
1947	Disclosure of movement of potential shares [line items]	LineItems			cstm:DisclosureOfMovementOfPotentialSharesLineItems
1948	Percentage of vesting multiplier	Concept (Percent)	For Period		cstm:PercentageOfSharebasedPaymentsVestingMultiplier
1949	Performance based shares forfeited upon departure of certain beneficiaries	Concept (Shares)	For Period		cstm:NumberOfOtherEquityInstrumentsForfeitedOnDepartureOfCertainBeneficiariesInSharebasedPaymentArrangement
1950	Performance based shares forfeited upon non-fulfilment of performance conditions	Concept (Shares)	For Period		cstm:NumberOfOtherEquityInstrumentsForfeitedOnNonFulfillmentOfPerformanceConditionsInSharebasedPaymentArrangement
1951	1181 - Disclosure - Subsidiaries and Operating Segments - Summary of Group's Affiliates are Included in Consolidated Financial Statements (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureSubsidiariesAndOperatingSegmentsSummaryOfGroupsAffiliatesAreIncludedInConsolidatedFinancialStatements
1952	Disclosure of subsidiaries [table]	Table	*	*	ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesTable
1953	Segments [axis]	Axis			ifrs-full:SegmentsAxis
1954	Segments [member]	Member			ifrs-full:SegmentsMember
1955	Cross operating segment [member]	Member			cstm:CrossOperatingSegmentMember
1956	AS&I [member]	Member			cstm:AutomotiveStructuresAndIndustryMember
1957	A&T [member]	Member			cstm:AerospaceAndTransportationMember
1958	P&ARP [member]	Member			cstm:PackagingAndAutomotiveRolledProductsMember
1959	Holdings & Corporate [member]	Member			cstm:HoldingsAndCorporateMember
1960	Subsidiaries [axis]	Axis			ifrs-full:SignificantInvestmentsInSubsidiariesAxis
1961	Entity's total for subsidiaries [member]	Member			ifrs-full:EntitysTotalForSubsidiariesMember
1962	Constellium Singen GmbH [member]	Member			cstm:ConstelliumSingenGmbHMember
1963	Constellium Valais S.A. [member]	Member			cstm:ConstelliumValaisSAMember
1964	Constellium Automotive USA, LLC [member]	Member			cstm:ConstelliumAutomotiveUSALLCMember
1965	Constellium Engley (Changchun) Automotive Structures Co Ltd. [member]	Member			cstm:ConstelliumEngleyChangchunAutomotiveStructuresCoLtdMember
1966	Constellium Extrusions Decin S.r.o. [member]	Member			cstm:ConstelliumExtrusionsDecinSroMember
1967	Constellium Extrusions Deutschland GmbH [member]	Member			cstm:ConstelliumExtrusionsDeutschlandGmbHMember
1968	Constellium Extrusions Landau GmbH [member]	Member			cstm:ConstelliumExtrusionsLandauGmbHMember
1969	Constellium Extrusions Burg GmbH [member]	Member			cstm:ConstelliumExtrusionsBurgGmbHMember
1970	Constellium Extrusions France S.A.S. [member]	Member			cstm:ConstelliumExtrusionsFranceSASMember
1971	Constellium Extrusions Levice S.r.o. [member]	Member			cstm:ConstelliumExtrusionsLeviceSroMember
1972	Constellium Automotive Mexico, S. DE R.L. DE C.V. [member]	Member			cstm:ConstelliumAutomotiveMexicoSDERLDECVMember
1973	Constellium Automotive Mexico Trading, S. DE R.L. DE C.V [member]	Member			cstm:ConstelliumAutomotiveMexicoTradingSDERLDECVMember
1974	Astrex Inc [member]	Member			cstm:AstrexIncMember
1975	Constellium Automotive Zilina S.r.o. [member]	Member			cstm:ConstelliumAutomotiveZilinaSroMember
1976	Constellium Automotive Nanjing Co Ltd [member]	Member			cstm:ConstelliumAutomotiveNanjingCoLtdMember
1977	Constellium Automotive Spain SL [member]	Member			cstm:ConstelliumAutomotiveSpainSLMember
1978	Constellium Issoire S.A.S. [member]	Member			cstm:ConstelliumIssoireSASMember
1979	Constellium Montreuil Juigne S.A.S. [member]	Member			cstm:ConstelliumMontreuilJuigneMember
1980	Constellium China Limited [member]	Member			cstm:ConstelliumChinaLimitedMember
1981	Constellium Japan KK [member]	Member			cstm:ConstelliumJapanKKMember
1982	Constellium Rolled Products Ravenswood, LLC [member]	Member			cstm:ConstelliumRolledProductsRavenswoodLLCMember
1983	Constellium Southeast Asia PTE LTD [member]	Member			cstm:ConstelliumSoutheastAsiaPTELTDMember
1984	Constellium Ussel S.A.S. [member]	Member			cstm:ConstelliumUsselSASMember
1985	AluInfra Services SA [member]	Member			cstm:AluinfraServicesSAMember
1986	Constellium Deutschland GmbH [member]	Member			cstm:ConstelliumDeutschlandGmbHMember
1987	Constellium Rolled Products Singen GmbH KG [member]	Member			cstm:ConstelliumRolledProductsSingenGmbHKGMember
1988	Constellium Property and Equipment Company LLC [member]	Member			cstm:ConstelliumPropertyAndEquipmentCompanyLLCMember
1989	Constellium Neuf Brisach [member]	Member			cstm:ConstelliumNeufBrisachMember
1990	Constellium Muscle Shoals LLC [member]	Member			cstm:ConstelliumMuscleShoalsLLCMember
1991	Constellium Holding Muscle Shoals LLC [member]	Member			cstm:ConstelliumHoldingMuscleShoalsLLCMember
1992	Constellium Muscle Shoals Funding II LLC [member]	Member			cstm:ConstelliumMuscleShoalsFundingTwoLLCMember
1993	Listerhill Total Maintenance Center LLC [member]	Member			cstm:ListerhillTotalMaintenanceCenterLlcMember
1994	Constellium Metal Procurement LLC [member]	Member			cstm:ConstelliumMetalProcurementLLCMember
1995	Constellium-Bowling Green [member]	Member			cstm:ConstelliumUACJABSLLCMember
1996	Rhenaroll [member]	Member			cstm:RhenarollMember
1997	C-TEC Constellium Technology Center S.A.S. [member]	Member			cstm:CtecConstelliumTechnologyCenterSASMember
1998	Constellium Finance S.A.S. [member]	Member			cstm:ConstelliumFinanceSASMember
1999	Constellium France III [member]	Member			cstm:ConstelliumFranceIIIMember
2000	Constellium France Holdco S.A.S. [member]	Member			cstm:ConstelliumFranceHoldcoSASMember
2001	Constellium International [member]	Member			cstm:ConstelliumInternationalMember
2002	Constellium Paris S.A.S [member]	Member			cstm:ConstelliumParisSASMember
2003	Constellium Germany Holdco GmbH & Co. KG [member]	Member			cstm:ConstelliumGermanyHoldcoGmbHAndCoKGMember
2004	Constellium Germany Verwaltungs GmbH [member]	Member			cstm:ConstelliumGermanyVerwaltungsGmbhMember
2005	Constellium UK Limited [member]	Member			cstm:ConstelliumUKLimitedMember
2006	Constellium U.S. Holdings I, LLC [member]	Member			cstm:ConstelliumUSHoldingsILLCMember
2007	Constellium Switzerland AG [member]	Member			cstm:ConstelliumSwitzerlandAGMember
2008	Constellium W S.A.S. [member]	Member			cstm:ConstelliumWSASMember
2009	Constellium Treuhand UG [member]	Member			cstm:ConstelliumTreuhandUGMember
2010	Engineered Products International S.A.S. [member]	Member			cstm:EngineeredProductsInternationalSASMember
2011	Disclosure of subsidiaries [line items]	LineItems			ifrs-full:DisclosureOfSignificantInvestmentsInSubsidiariesLineItems
2012	Country	Concept (Text/String)	For Period		ifrs-full:CountryOfIncorporationOrResidenceOfSubsidiary
2013	Percentage Group Interest	Concept (Percent)	For Period		ifrs-full:ProportionOfOwnershipInterestInSubsidiary
2014	Consolidation Method	Concept (Text/String)	For Period		cstm:DescriptionOfConsolidationMethod
2015	1182 - Disclosure - Parent Company - Statement of Financial Position of Constellium N.V. (Parent Company Only) (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureParentCompanyStatementOfFinancialPositionOfConstelliumNVParentCompanyOnly
2016	Disclosure of condensed financial information of parent company [table]	Table	*	*	cstm:DisclosureOfCondensedFinancialInformationOfParentCompanyTable
2017	Categories of related parties [axis]	Axis			ifrs-full:CategoriesOfRelatedPartiesAxis
2018	Entity's total for related parties [member]	Member			ifrs-full:EntitysTotalForRelatedPartiesMember
2019	Parent [member]	Member			ifrs-full:ParentMember
2020	Disclosure of condensed financial information of parent company [line items]	LineItems			cstm:DisclosureOfCondensedFinancialInformationOfParentCompanyLineItems
2021	Assets	Abstract			ifrs-full:AssetsAbstract
2022	Current assets	Abstract			ifrs-full:CurrentAssetsAbstract
2023	Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
2024	Trade receivables and other	Concept (Monetary)	As Of	Debit	ifrs-full:TradeAndOtherCurrentReceivables
2025	Other financial assets	Concept (Monetary)	As Of	Debit	ifrs-full:OtherCurrentFinancialAssets
2026	Total current assets	Concept (Monetary)	As Of	Debit	ifrs-full:CurrentAssets
2027	Non-current assets	Abstract			ifrs-full:NoncurrentAssetsAbstract
2028	Property, plant and equipment	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipment
2029	Financial assets	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentFinancialAssets
2030	Investments in subsidiaries	Concept (Monetary)	As Of	Debit	ifrs-full:InvestmentsInSubsidiaries
2031	Deferred income tax assets	Concept (Monetary)	As Of	Debit	ifrs-full:DeferredTaxAssets
2032	Total non-current assets	Concept (Monetary)	As Of	Debit	ifrs-full:NoncurrentAssets
2033	Total Assets	Concept (Monetary)	As Of	Debit	ifrs-full:Assets
2034	Liabilities	Abstract			ifrs-full:LiabilitiesAbstract
2035	Current liabilities	Abstract			ifrs-full:CurrentLiabilitiesAbstract
2036	Trade payables and other	Concept (Monetary)	As Of	Credit	ifrs-full:TradeAndOtherCurrentPayables
2037	Income tax payable	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentTaxLiabilities
2038	Other financial liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:OtherCurrentFinancialLiabilities
2039	Total current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:CurrentLiabilities
2040	Non-current liabilities	Abstract			ifrs-full:NoncurrentLiabilitiesAbstract
2041	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:LongtermBorrowings
2042	Total non-current liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:NoncurrentLiabilities
2043	Total Liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:Liabilities
2044	Equity	Abstract			ifrs-full:EquityAbstract
2045	Share capital	Concept (Monetary)	As Of	Credit	ifrs-full:IssuedCapital
2046	Share premium	Concept (Monetary)	As Of	Credit	ifrs-full:SharePremium
2047	Accumulated retained earnings	Concept (Monetary)	As Of	Credit	ifrs-full:RetainedEarnings
2048	Other reserves	Concept (Monetary)	As Of	Credit	ifrs-full:OtherReserves
2049	Net income/ (loss)	Concept (Monetary)	As Of	Credit	cstm:NetIncomeLossCapitalizedToStockholders
2050	Total Equity	Concept (Monetary)	As Of	Credit	ifrs-full:Equity
2051	Total Equity and Liabilities	Concept (Monetary)	As Of	Credit	ifrs-full:EquityAndLiabilities
2052	1183 - Disclosure - Parent Company - Statement of Comprehensive Income / (Loss) of Constellium N.V. (Parent Company Only) (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureParentCompanyStatementOfComprehensiveIncomeLossOfConstelliumNVParentCompanyOnly
2053	Disclosure of condensed financial information of parent company [table]	Table	*	*	cstm:DisclosureOfCondensedFinancialInformationOfParentCompanyTable
2054	Categories of related parties [axis]	Axis			ifrs-full:CategoriesOfRelatedPartiesAxis
2055	Entity's total for related parties [member]	Member			ifrs-full:EntitysTotalForRelatedPartiesMember
2056	Parent [member]	Member			ifrs-full:ParentMember
2057	Disclosure of condensed financial information of parent company [line items]	LineItems			cstm:DisclosureOfCondensedFinancialInformationOfParentCompanyLineItems
2058	Revenue	Concept (Monetary)	For Period	Credit	ifrs-full:Revenue
2059	Gross profit	Concept (Monetary)	For Period	Credit	ifrs-full:GrossProfit
2060	Selling and administrative expenses	Concept (Monetary)	For Period	Debit	ifrs-full:SellingGeneralAndAdministrativeExpense
2061	Employee benefit expenses	Concept (Monetary)	For Period	Debit	ifrs-full:EmployeeBenefitsExpense
2062	Loss from recurring operations	Concept (Monetary)	For Period	Credit	cstm:OperatingMargin
2063	Other income	Concept (Monetary)	For Period	Credit	ifrs-full:OtherIncome
2064	Other expense	Concept (Monetary)	For Period	Debit	ifrs-full:OtherExpenseByFunction
2065	(Loss) / Income from operations	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossFromOperatingActivities
2066	Financial result-net	Concept (Monetary)	For Period	Credit	ifrs-full:FinanceIncomeCost
2067	Income / (loss) before income tax	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossBeforeTax
2068	Income tax (expense) / benefit	Concept (Monetary)	For Period	Debit	ifrs-full:IncomeTaxExpenseContinuingOperations
2069	Net income / (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
2070	Other comprehensive (loss) / income	Concept (Monetary)	For Period	Credit	ifrs-full:OtherComprehensiveIncome
2071	Total comprehensive income / (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ComprehensiveIncome
2072	1184 - Disclosure - Parent Company - Statement of Cash Flows of Constellium N.V. (Parent Company Only) (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureParentCompanyStatementOfCashFlowsOfConstelliumNVParentCompanyOnly
2073	Disclosure of condensed financial information of parent company [table]	Table	*	*	cstm:DisclosureOfCondensedFinancialInformationOfParentCompanyTable
2074	Categories of related parties [axis]	Axis			ifrs-full:CategoriesOfRelatedPartiesAxis
2075	Entity's total for related parties [member]	Member			ifrs-full:EntitysTotalForRelatedPartiesMember
2076	Parent [member]	Member			ifrs-full:ParentMember
2077	Disclosure of condensed financial information of parent company [line items]	LineItems			cstm:DisclosureOfCondensedFinancialInformationOfParentCompanyLineItems
2078	Net income/ (loss)	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLoss
2079	Adjustments	Abstract			ifrs-full:AdjustmentsForReconcileProfitLossAbstract
2080	Finance cost-net	Concept (Monetary)	For Period	Credit	ifrs-full:AdjustmentsForFinanceIncomeCost
2081	Dividend received	Concept (Monetary)	For Period	Credit	ifrs-full:AdjustmentsForDividendIncome
2082	Income tax	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForIncomeTaxExpense
2083	Interest paid	Concept (Monetary)	For Period	Credit	ifrs-full:InterestPaidClassifiedAsOperatingActivities
2084	Interest received	Concept (Monetary)	For Period	Credit	ifrs-full:AdjustmentsForInterestIncome
2085	Changes in working capital	Abstract			cstm:AdjustmentsForIncreaseDecreaseInWorkingCapitalAbstract
2086	Trade receivables and other	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForDecreaseIncreaseInTradeAndOtherReceivables
2087	Other financial liabilities	Concept (Monetary)	For Period	Debit	cstm:AdjustmentsForIncreaseDecreaseInOtherFinancialLiabilities
2088	Trade payables and other	Concept (Monetary)	For Period	Debit	ifrs-full:AdjustmentsForIncreaseDecreaseInTradeAndOtherPayables
2089	Net cash flows from / (used in) operating activities	Concept (Monetary)	For Period		ifrs-full:CashFlowsFromUsedInOperations
2090	Investments in subsidiaries	Concept (Monetary)	For Period	Credit	cstm:PaymentForInvestmentsInSubsidiaries
2091	Current account with subsidiaries and related parties	Concept (Monetary)	For Period	Debit	cstm:ProceedsFromPaymentsForCurrentAccountWithSubsidiariesAndRelatedParties
2092	Loans granted to subsidiary and related parties	Concept (Monetary)	For Period	Credit	ifrs-full:CashAdvancesAndLoansMadeToRelatedParties
2093	Repayment of loans granted to subsidiary and related parties	Concept (Monetary)	For Period	Debit	ifrs-full:CashReceiptsFromRepaymentOfAdvancesAndLoansMadeToRelatedParties
2094	Exit fees received from subsidiaries	Concept (Monetary)	For Period	Debit	cstm:ExitFeesReceivedFromSubsidiaries
2095	Net cash flows used in investing activities	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromUsedInInvestingActivities
2096	Net proceeds received from issuance of shares	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromIssuingShares
2097	Proceeds from issuance of Senior Notes	Concept (Monetary)	For Period	Debit	ifrs-full:ProceedsFromIssueOfBondsNotesAndDebentures
2098	Payment of deferred financing costs	Concept (Monetary)	For Period	Credit	ifrs-full:PaymentsForDebtIssueCosts
2099	Repayment of Senior Notes	Concept (Monetary)	For Period	Credit	ifrs-full:RepaymentsOfBondsNotesAndDebentures
2100	Payment of exit fees	Concept (Monetary)	For Period	Credit	cstm:PaymentOfExitFees
2101	Realized foreign exchange gains / (losses)	Concept (Monetary)	For Period	Credit	cstm:ProceedsFromPaymentsForForeignExchangeTransactions
2102	Other	Concept (Monetary)	For Period	Debit	ifrs-full:OtherInflowsOutflowsOfCashClassifiedAsFinancingActivities
2103	Net cash flows (used in) / from financing activities	Concept (Monetary)	For Period	Debit	ifrs-full:CashFlowsFromUsedInFinancingActivities
2104	Net (decrease) / increase in cash and cash equivalents	Concept (Monetary)	For Period	Debit	ifrs-full:IncreaseDecreaseInCashAndCashEquivalentsBeforeEffectOfExchangeRateChanges
2105	Cash and cash equivalents-beginning of year	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
2106	Effect of exchange rate changes on cash and cash equivalents	Concept (Monetary)	For Period	Debit	ifrs-full:EffectOfExchangeRateChangesOnCashAndCashEquivalents
2107	Cash and cash equivalents-end of year	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalents
2108	1185 - Disclosure - Parent Company - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureParentCompanyAdditionalInformation
2109	Disclosure of condensed financial information of parent company [table]	Table	*	*	cstm:DisclosureOfCondensedFinancialInformationOfParentCompanyTable
2110	Initially applied IFRSs [axis]	Axis			ifrs-full:InitiallyAppliedIFRSsAxis
2111	Initially applied IFRSs [member]	Member			ifrs-full:InitiallyAppliedIFRSsMember
2112	IFRS9 [member]	Member			cstm:IFRS9Member
2113	Disclosure of condensed financial information of parent company [line items]	LineItems			cstm:DisclosureOfCondensedFinancialInformationOfParentCompanyLineItems
2114	Loss on opening retained earnings, net of tax	Concept (Monetary)	For Period	Credit	cstm:GainLossOnOpeningRetainedEarningsNet
2115	Loss allowance	Concept (Monetary)	As Of	Debit	cstm:ExpectedCreditLossAllowance
2116	Gain on other comprehensive income	Concept (Monetary)	For Period	Credit	cstm:GainLossOnOtherComprehensiveIncome
2117	1186 - Disclosure - Acquisition of Constellium-Bowling Green - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureAcquisitionOfConstelliumBowlingGreenAdditionalInformation
2118	Disclosure of detailed information about business combination [table]	Table	*	*	ifrs-full:DisclosureOfBusinessCombinationsTable
2119	Business combinations [axis]	Axis			ifrs-full:BusinessCombinationsAxis
2120	Entity's total for business combinations [member]	Member			ifrs-full:EntitysTotalForBusinessCombinationsMember
2121	Constellium-Bowling Green [member]	Member			cstm:ConstelliumUACJABSLLCMember
2122	Non-adjusting events after reporting period [axis]	Axis			ifrs-full:NonadjustingEventsAfterReportingPeriodAxis
2123	Non-adjusting events after reporting period [member]	Member			ifrs-full:NonadjustingEventsMember
2124	Major business combination [member]	Member			ifrs-full:MajorBusinessCombinationMember
2125	Disclosure of detailed information about business combination [line items]	LineItems			ifrs-full:DisclosureOfBusinessCombinationsLineItems
2126	Percentage of voting equity interests acquired	Concept (Percent)	As Of		ifrs-full:PercentageOfVotingEquityInterestsAcquired
2127	Consideration transferred	Concept (Monetary)	As Of	Credit	ifrs-full:CashTransferred
2128	Fair value of previously held interest	Concept (Monetary)	As Of	Credit	ifrs-full:AcquisitiondateFairValueOfEquityInterestInAcquireeHeldByAcquirerImmediatelyBeforeAcquisitionDate
2129	Preexisting trade receivables with acquiree	Concept (Monetary)	As Of	Debit	ifrs-full:TradeReceivables
2130	Combined revenue	Concept (Monetary)	For Period	Credit	ifrs-full:RevenueOfCombinedEntity
2131	Combined net income	Concept (Monetary)	For Period	Credit	ifrs-full:ProfitLossOfCombinedEntity
2132	1187 - Disclosure - Acquisition of Constellium-Bowling Green - Summary of Preliminary Goodwill Arising as a Result of Preliminary Allocation of Purchase Price to Assets Acquired and Liabilities Assumed (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureAcquisitionOfConstelliumBowlingGreenSummaryOfPreliminaryGoodwillArisingAsAResultOfPreliminaryAllocationOfPurchasePriceToAssetsAcquiredAndLiabilitiesAssumed
2133	Disclosure of detailed information about business combination [table]	Table	*	*	ifrs-full:DisclosureOfBusinessCombinationsTable
2134	Business combinations [axis]	Axis			ifrs-full:BusinessCombinationsAxis
2135	Entity's total for business combinations [member]	Member			ifrs-full:EntitysTotalForBusinessCombinationsMember
2136	Constellium-Bowling Green [member]	Member			cstm:ConstelliumUACJABSLLCMember
2137	Non-adjusting events after reporting period [axis]	Axis			ifrs-full:NonadjustingEventsAfterReportingPeriodAxis
2138	Non-adjusting events after reporting period [member]	Member			ifrs-full:NonadjustingEventsMember
2139	Major business combination [member]	Member			ifrs-full:MajorBusinessCombinationMember
2140	Disclosure of detailed information about business combination [line items]	LineItems			ifrs-full:DisclosureOfBusinessCombinationsLineItems
2141	Cash and cash equivalents	Concept (Monetary)	As Of	Debit	ifrs-full:CashAndCashEquivalentsRecognisedAsOfAcquisitionDate
2142	Trade receivables and other	Concept (Monetary)	As Of	Debit	cstm:TradeReceivablesAndOtherRecognisedAsOfAcquisitionDate
2143	Inventories	Concept (Monetary)	As Of	Debit	ifrs-full:InventoryRecognisedAsOfAcquisitionDate
2144	Property, plant and equipment	Concept (Monetary)	As Of	Debit	ifrs-full:PropertyPlantAndEquipmentRecognisedAsOfAcquisitionDate
2145	Trade payables and other	Concept (Monetary)	As Of	Credit	ifrs-full:TradeAndOtherPayablesRecognisedAsOfAcquisitionDate
2146	Borrowings	Concept (Monetary)	As Of	Credit	ifrs-full:BorrowingsRecognisedAsOfAcquisitionDate
2147	Net asset acquired at fair value	Concept (Monetary)	As Of	Debit	ifrs-full:IdentifiableAssetsAcquiredLiabilitiesAssumed
2148	Preliminary Goodwill	Concept (Monetary)	As Of	Debit	ifrs-full:GoodwillRecognisedAsOfAcquisitionDate
2149	Total Consideration	Concept (Monetary)	As Of	Credit	ifrs-full:AcquisitiondateFairValueOfTotalConsiderationTransferred
2150	1188 - Disclosure - Subsequent Events - Additional Information (Detail)	Network	*	*	http://www.constellium.com/taxonomy/role/DisclosureSubsequentEventsAdditionalInformation
2151	Disclosure of non-adjusting events after reporting period [table]	Table	*	*	ifrs-full:DisclosureOfNonadjustingEventsAfterReportingPeriodTable
2152	Non-adjusting events after reporting period [axis]	Axis			ifrs-full:NonadjustingEventsAfterReportingPeriodAxis
2153	Non-adjusting events after reporting period [member]	Member			ifrs-full:NonadjustingEventsMember
2154	Major business combination [member]	Member			ifrs-full:MajorBusinessCombinationMember
2155	Business combinations [axis]	Axis			ifrs-full:BusinessCombinationsAxis
2156	Entity's total for business combinations [member]	Member			ifrs-full:EntitysTotalForBusinessCombinationsMember
2157	Constellium-Bowling Green [member]	Member			cstm:ConstelliumUACJABSLLCMember
2158	Range [axis]	Axis			ifrs-full:RangeAxis
2159	Ranges [member]	Member			ifrs-full:RangesMember
2160	Top of range [member]	Member			ifrs-full:TopOfRangeMember
2161	Borrowings by name [axis]	Axis			ifrs-full:BorrowingsByNameAxis
2162	Borrowings by name [member]	Member			ifrs-full:BorrowingsByNameMember
2163	Pan US ABL Facility [member]	Member			cstm:PanUSABLFacilityMember
2164	Disclosure of non-adjusting events after reporting period [line items]	LineItems			ifrs-full:DisclosureOfNonadjustingEventsAfterReportingPeriodLineItems
2165	Percentage of voting equity interest acquired	Concept (Percent)	As Of		ifrs-full:PercentageOfVotingEquityInterestsAcquired
2166	Increase in commitments	Concept (Monetary)	For Period	Credit	cstm:IncreaseDecreaseInCommitments