XML 76 R68.htm IDEA: XBRL DOCUMENT
v3.20.2

EARNINGS PER SHARE - Number of Shares Attributable to Equity Holders (Details) - shares | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019
Earnings per share [abstract] |  |  |  |
Weighted average number of ordinary shares used to calculate basic earnings per share (in shares) | 137,901,336 | 136,700,491 | 137,903,307 | 136,344,030
Effect of other dilutive potential ordinary shares (in shares) | 0 | 3,620,938 | 0 | 4,005,235
Weighted average number of ordinary shares used to calculate diluted earnings per share (in shares) | 137,901,336 | 140,321,429 | 137,903,307 | 140,349,265
Potential ordinary shares (in shares) | 4,880,758 |  | 4,878,787 |

X
- Definition Calculation of diluted potential ordinary shares. + References No definition available. + Details
Name: | cstm_CalculationOfDilutedPotentialOrdinaryShares
Namespace Prefix: | cstm_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition The weighted average number of ordinary shares outstanding plus the weighted average number of ordinary shares that would be issued on the conversion of all the dilutive potential ordinary shares into ordinary shares. [Refer: Ordinary shares [member]; Weighted average [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 33 -IssueDate 2019-01-01 -Paragraph 70 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=33&code=ifrs-tx-2019-en-r&anchor=para_70_b&doctype=Standard -URIDate 2019-03-27 + Details
Name: | ifrs-full_AdjustedWeightedAverageShares
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of dilutive potential ordinary shares that relate to the assumed exercise of the entity's share options. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 33 -IssueDate 2019-01-01 -Paragraph 70 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=33&code=ifrs-tx-2019-en-r&anchor=para_70_b&doctype=Standard -URIDate 2019-03-27 + Details
Name: | ifrs-full_DilutiveEffectOfShareOptionsOnNumberOfOrdinaryShares
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | ifrs-full_EarningsPerShareAbstract
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of ordinary shares outstanding at the beginning of the period, adjusted by the number of ordinary shares bought back or issued during the period multiplied by a time-weighting factor. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 33 -IssueDate 2019-01-01 -Paragraph 70 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=33&code=ifrs-tx-2019-en-r&anchor=para_70_b&doctype=Standard -URIDate 2019-03-27 + Details
Name: | ifrs-full_WeightedAverageShares
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration