XML 218 R176.htm IDEA: XBRL DOCUMENT
v3.19.1

Share-Based Compensation - Additional Information (Detail) € in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Nov. 30, 2018 shares | Dec. 31, 2018 EUR (€) shares | Dec. 31, 2017 EUR (€) shares | Dec. 31, 2016 EUR (€) shares
Share Based Payment Plans [line items] |  |  |  |
Total expense related to the potential ordinary shares | € |  | € 12 | € 8 | € 6
Restricted Stock Units [member] |  |  |  |
Share Based Payment Plans [line items] |  |  |  |
Number of shares granted |  |  |  | 150,000
Vesting period on the grant date |  | 3 years |  |
Description of vesting requirements for share-based payment arrangement |  |  |  | In 2016, the Company also granted 150,000 RSUs which vest in equal installments on the first two anniversaries of the grant date, subject to continued employment, of which 75,000 vested on the first anniversary in 2017 and 75,000 in 2018 on the second anniversary.
Number of RSU vested |  | 75,000 | 75,000 |
Equity Awards Plans [member] |  |  |  |
Share Based Payment Plans [line items] |  |  |  |
Description of vesting requirements for share-based payment arrangement |  | Company Board members have been granted RSU awards annually since 2012. These RSUs vest in equal installments on the first two anniversaries of the date of grant, subject to their continued service. |  |
Performance share units (PSUs) [member] |  |  |  |
Share Based Payment Plans [line items] |  |  |  |
Share based compensation, vesting period |  | 3 years |  |
Percentage of vesting multiplier |  | 100.00% |  |
PSUs granted in 2015 and 2016 [member] | Bottom of range [member] |  |  |  |
Share Based Payment Plans [line items] |  |  |  |
Percentage of vesting multiplier |  | 0.00% |  |
PSUs granted in 2015 and 2016 [member] | Top of range [member] |  |  |  |
Share Based Payment Plans [line items] |  |  |  |
Percentage of vesting multiplier |  | 300.00% |  |
PSUs granted in 2017 and 2018 [member] |  |  |  |
Share Based Payment Plans [line items] |  |  |  |
Share based compensation, measurement period |  |  | 3 years |
PSUs granted in 2017 and 2018 [member] | Bottom of range [member] |  |  |  |
Share Based Payment Plans [line items] |  |  |  |
Percentage of vesting |  |  | 0.00% |
PSUs granted in 2017 and 2018 [member] | Top of range [member] |  |  |  |
Share Based Payment Plans [line items] |  |  |  |
Percentage of vesting |  |  | 200.00% |
PSUs granted in November 2015 [member] |  |  |  |
Share Based Payment Plans [line items] |  |  |  |
Total Stockholders return percentage achieved |  | 184.40% | 251.10% | 118.20%
Potential additional shares to be vested |  | 187,648 | 366,669 | 47,229
Vesting date of additional shares |  | November 2018 | November 2018 | November 2018
Number of shares granted | 1,231,055 |  |  |
PSUs granted in March 2016 [member] |  |  |  |
Share Based Payment Plans [line items] |  |  |  |
Total Stockholders return percentage achieved |  | 229.90% | 115.90% |
PSUs granted in May 2016 [member] |  |  |  |
Share Based Payment Plans [line items] |  |  |  |
Total Stockholders return percentage achieved |  | 217.20% | 98.10% |
PSUs granted in August 2016 [member] |  |  |  |
Share Based Payment Plans [line items] |  |  |  |
Total Stockholders return percentage achieved |  | 282.20% | 191.60% |
PSUs granted in November 2016 [member] |  |  |  |
Share Based Payment Plans [line items] |  |  |  |
Total Stockholders return percentage achieved |  | 148.70% | 223.80% |
PSUs granted in 2016 [member] |  |  |  |
Share Based Payment Plans [line items] |  |  |  |
Potential additional shares to be vested |  | 446,022 | 186,059 |
Vesting date of additional shares |  | 2019 |  |

X
- Definition Number of other equity instruments vested in share-based payment arrangement. + References No definition available. + Details
Name: | cstm_NumberOfOtherEquityInstrumentsVestedInSharebasedPaymentArrangement
Namespace Prefix: | cstm_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of shares in other equity instruments (ie other than share options) granted in a share-based payment arrangement. + References No definition available. + Details
Name: | cstm_NumberOfSharesInOtherEquityInstrumentsGrantedInSharebasedPaymentArrangement
Namespace Prefix: | cstm_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of sharebased payments vesting. + References No definition available. + Details
Name: | cstm_PercentageOfSharebasedPaymentsVesting
Namespace Prefix: | cstm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of sharebased payments vesting multiplier. + References No definition available. + Details
Name: | cstm_PercentageOfSharebasedPaymentsVestingMultiplier
Namespace Prefix: | cstm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Potential additional shares to be vested. + References No definition available. + Details
Name: | cstm_PotentialAdditionalSharesToBeVested
Namespace Prefix: | cstm_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share based compensation measurement period. + References No definition available. + Details
Name: | cstm_ShareBasedCompensationMeasurementPeriod
Namespace Prefix: | cstm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share based compensation vesting period. + References No definition available. + Details
Name: | cstm_ShareBasedCompensationVestingPeriod
Namespace Prefix: | cstm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share based Payment Arrangement Vesting Period + References No definition available. + Details
Name: | cstm_ShareBasedPaymentArrangementVestingPeriod
Namespace Prefix: | cstm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share based payment plans. + References No definition available. + Details
Name: | cstm_ShareBasedPaymentPlansLineItems
Namespace Prefix: | cstm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Sharebased Compensation stockholders return percentage. + References No definition available. + Details
Name: | cstm_SharebasedCompensationStockholdersReturnPercentage
Namespace Prefix: | cstm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The description of the maximum term of options granted for a type of share-based payment arrangement that existed at any time during the period. An entity with substantially similar types of share-based payment arrangements may aggregate this information. [Refer: Share-based payment arrangements [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2018-01-01 -Paragraph 45 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2018-03-01&anchor=para_45_a&doctype=Standard -URIDate 2018-03-16 + Details
Name: | ifrs-full_DescriptionOfMaximumTermOfOptionsGrantedForSharebasedPaymentArrangement
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The description of the vesting requirements for a type of share-based payment arrangement that existed at any time during the period. An entity with substantially similar types of share-based payment arrangements may aggregate this information. [Refer: Share-based payment arrangements [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2018-01-01 -Paragraph 45 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2018-03-01&anchor=para_45_a&doctype=Standard -URIDate 2018-03-16 + Details
Name: | ifrs-full_DescriptionOfVestingRequirementsForSharebasedPaymentArrangement
Namespace Prefix: | ifrs-full_
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 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_ExpenseFromSharebasedPaymentTransactionsWithEmployees
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | ifrs-full_TypesOfSharebasedPaymentArrangementsAxis=cstm_RestrictedStockUnitsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TypesOfSharebasedPaymentArrangementsAxis=cstm_EquityAwardsPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TypesOfSharebasedPaymentArrangementsAxis=cstm_PerformanceShareUnitsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TypesOfSharebasedPaymentArrangementsAxis=cstm_PerformanceShareUnitsGrantedInTwoThousandAndFifteenAndTwoThousandAndSixteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_RangeAxis=ifrs-full_BottomOfRangeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_RangeAxis=ifrs-full_TopOfRangeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TypesOfSharebasedPaymentArrangementsAxis=cstm_PerformanceShareUnitsGrantedInTwoThousandAndSeventeenAndTwoThousandAndEighteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TypesOfSharebasedPaymentArrangementsAxis=cstm_PerformanceShareUnitsGrantedInNovemberTwoThousandAndFifteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TypesOfSharebasedPaymentArrangementsAxis=cstm_PerformanceShareUnitsGrantedInMarchTwoThousandAndSixteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TypesOfSharebasedPaymentArrangementsAxis=cstm_PerformanceShareUnitsGrantedInMayTwoThousandAndSixteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TypesOfSharebasedPaymentArrangementsAxis=cstm_PerformanceShareUnitsGrantedInAugustTwoThousandAndSixteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TypesOfSharebasedPaymentArrangementsAxis=cstm_PerformanceShareUnitsGrantedInNovemberTwoThousandAndSixteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TypesOfSharebasedPaymentArrangementsAxis=cstm_PerformanceShareUnitsGrantedInTwoThousandAndSixteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |