XML 213 R171.htm IDEA: XBRL DOCUMENT
v3.19.1

Commitments - Additional Information (Detail) - EUR (€) € in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Disclosure of operating lease [abstract] |  |  |
Rent expense | € 31 | € 27 | € 27

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- Definition Disclosure of operating lease. + References No definition available. + Details
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Namespace Prefix: | cstm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The amount of expense recognised on rental activities. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 85 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_85&doctype=Standard -URIDate 2018-03-16 + Details
Name: | ifrs-full_RentalExpense
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration