XML 169 R132.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Financial Instruments - Additional Information (Detail) - Fair value [member] € in Millions | Dec. 31, 2017 EUR (€)
--- | ---
Constellium N.V. senior unsecured notes (Issued May 2014) [member] |
Disclosure of detailed information about financial instruments [line items] |
Percentage of fair value senior notes issued | 102.00%
Senior Notes issued | € 645
Constellium N.V. Senior Unsecured Notes (Issued February 2017, due 2025) [member] |
Disclosure of detailed information about financial instruments [line items] |
Percentage of fair value senior notes issued | 106.00%
Senior Notes issued | € 572
Constellium N.V. EUR and USD Senior Unsecured Notes (Issued November 2017, due 2026) [member] |
Disclosure of detailed information about financial instruments [line items] |
Percentage of fair value senior notes issued | 101.00%
Senior Notes issued | € 828

X
- Definition Percentage of fair value senior notes issued. + References No definition available. + Details
Name: | cstm_PercentageOfFairValueSeniorNotesIssued
Namespace Prefix: | cstm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Senior notes fair value. + References No definition available. + Details
Name: | cstm_SeniorNotesFairValue
Namespace Prefix: | cstm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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_DisclosureOfFinancialInstrumentsLineItems
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | ifrs-full_BorrowingsByNameAxis=cstm_ConstelliumNVSeniorUnsecuredNotesIssuedMayTwoThousandFourteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_MeasurementAxis=ifrs-full_AtFairValueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_BorrowingsByNameAxis=cstm_ConstelliumNvSeniorUnsecuredNotesIssuedFebruaryTwoThousandSeventeenDueTwoThousandTwentyFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_BorrowingsByNameAxis=cstm_ConstelliumNVEURAndUSDSeniorUnsecuredNotesIssuedNovemberTwoThousandSeventeenDueTwoThousandTwentySixMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |