XML 65 R58.htm IDEA: XBRL DOCUMENT v3.10.0.1

Revenue - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2018
Disclosure of geographical areas [abstract]
Percentage of payment option over total revenue	1.00%

X

- Definition

Percentage Revenues not recognized at a point in time.

+ References

No definition available.

+ Details

Name:	cstm_PercentageRevenuesNotRecognizedAtPointInTime
Namespace Prefix:	cstm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

Name:	ifrs-full_DisclosureOfGeographicalAreasAbstract
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration