XML 116 R109.htm IDEA: XBRL DOCUMENT v3.10.0.1

Share-Based Compensation - Additional Information (Detail) - EUR (€) € in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Share Based Payment Plans [line items]
Total expense related to the potential ordinary shares	€ 6	€ 3
2018 performance shares [member] | Bottom of range [member]
Share Based Payment Plans [line items]
Percentage of vesting multiplier	0.00%
2018 performance shares [member] | Top of range [member]
Share Based Payment Plans [line items]
Percentage of vesting multiplier	200.00%
Performance share units (PSUs) [member]
Share Based Payment Plans [line items]
Share based compensation, vesting period	3 years
Percentage of vesting multiplier	100.00%

X

- Definition

Percentage of sharebased payments vesting multiplier.

+ References

No definition available.

+ Details

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

X

- Definition

Share based compensation vesting period.

+ References

No definition available.

+ Details

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Namespace Prefix:	cstm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Share based payment plans.

+ References

No definition available.

+ Details

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

X

- Definition

The amount of expense from share-based payment transactions with employees.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_112_c&doctype=Standard
-URIDate 2017-03-09

+ Details

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

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Namespace Prefix:
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- Details

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X

- Details

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X

- Details

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Namespace Prefix:
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