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Operating Segment Information - Summary of Segment Revenue (Parenthetical) (Detail) € in Millions | 12 Months Ended
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Dec. 31, 2016 EUR (€)
Holdings & Corporate [member] |
Disclosure of operating segments [line items] |
One-time payment related to the re-negotiation of contract with customer | € 20

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- Definition One time payment related to renegotiation of contract with customer. + References No definition available. + Details
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Namespace Prefix: | cstm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
Name: | ifrs-full_DisclosureOfOperatingSegmentsLineItems
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | ifrs-full_SegmentsAxis=cstm_HoldingsAndCorporateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |