XML 64 R56.htm IDEA: XBRL DOCUMENT v3.19.2

General Information - Additional Information (Detail)	Jun. 30, 2019 Employees Facility site Center
Disclosure of general information [abstract]
Number of production facilities | Facility	26
Number of administrative and commercial sites | site	3
Number of R&D centers | Center	3
Number of employees | Employees	13,000

X

- Definition

Disclosure of general information.

+ References

No definition available.

+ Details

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

X

- Definition

Number of administrative and commercial sites.

+ References

No definition available.

+ Details

Name:	cstm_NumberOfAdministrativeAndCommercialSites
Namespace Prefix:	cstm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Number of production facilities.

+ References

No definition available.

+ Details

Name:	cstm_NumberOfProductionFacilities
Namespace Prefix:	cstm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Number of world class technology center.

+ References

No definition available.

+ Details

Name:	cstm_NumberOfWorldClassTechnologyCenter
Namespace Prefix:	cstm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The number of personnel employed by the entity at a date.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2018-01-01
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_112_c&doctype=Standard
-URIDate 2018-03-16

+ Details

Name:	ifrs-full_NumberOfEmployees
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant