XML 95 R88.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Borrowings - Summary of Borrowings (Parenthetical) (Detail) € in Millions | Mar. 28, 2018 EUR (€)
--- | ---
Unsecured revolving credit facilities [Member] |
Disclosure of detailed information about borrowings [line items] |
Borrowing capacity | € 10

X
- Definition Borrowing capacity under revolving credit facility. + References No definition available. + Details
Name: | cstm_BorrowingCapacityUnderRevolvingCreditFacility
Namespace Prefix: | cstm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

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