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

X

- Definition

Disclosure of operating lease.

+ References

No definition available.

+ Details

Name:	cstm_DisclosureOfOperatingLeaseAbstract
Namespace Prefix:	cstm_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- 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