XML 115 R108.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Share Capital - Schedule of Share Capital (Parenthetical) (Detail) | 6 Months Ended
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Jun. 30, 2018 shares
Disclosure of classes of share capital [line items] |
Share issued | 182,716
Ordinary shares [member] |
Disclosure of classes of share capital [line items] |
Treasury shares held | 38,597
Employees [member] | Common shares [member] |
Disclosure of classes of share capital [line items] |
Share issued | 182,716

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- Definition Number of auto-controlled shares. + References No definition available. + Details
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Namespace Prefix: | cstm_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
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Balance Type: | na
Period Type: | duration

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- Definition The increase (decrease) in the number of ordinary shares issued. [Refer: Ordinary shares [member]] + 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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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |