XML 195 R153.htm IDEA: XBRL DOCUMENT
v3.19.1

Financial Risk Management - Summary of Undiscounted Contractual Financial Assets and Financial Liabilities Values by Relevant Maturity Groupings (Detail) - EUR (€) € in Millions | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Less than 1 year [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial assets | € 27 | € 65
Financial liabilities | 1,079 | 1,110
Less than 1 year [member] | Borrowings [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial liabilities | 6 | 67
Less than 1 year [member] | Interests [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial liabilities | 114 | 103
Less than 1 year [member] | Net debt derivative liabilities [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial liabilities | 3 | 3
Less than 1 year [member] | Net cash flows from derivative liabilities related to currencies and commodities [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial liabilities | 56 | 17
Less than 1 year [member] | Trade payables and other (excluding deferred revenue and contract liabilities) [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial liabilities | 900 | 920
Less than 1 year [member] | Net debt derivative assets [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial assets | 5 | 6
Less than 1 year [member] | Net cash flows from derivatives assets related to currencies and commodities [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial assets | 22 | 59
Expiring within 5 years [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial assets | 24 | 18
Financial liabilities | 794 | 780
Expiring within 5 years [member] | Borrowings [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial liabilities | 315 | 318
Expiring within 5 years [member] | Interests [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial liabilities | 422 | 421
Expiring within 5 years [member] | Net debt derivative liabilities [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial liabilities | 4 | 10
Expiring within 5 years [member] | Net cash flows from derivative liabilities related to currencies and commodities [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial liabilities | 35 | 11
Expiring within 5 years [member] | Trade payables and other (excluding deferred revenue and contract liabilities) [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial liabilities | 18 | 20
Expiring within 5 years [member] | Net debt derivative assets [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial assets | 12 | 3
Expiring within 5 years [member] | Net cash flows from derivatives assets related to currencies and commodities [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial assets | 12 | 15
More than 5 years [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial liabilities | 1,927 | 1,956
More than 5 years [member] | Borrowings [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial liabilities | 1,754 | 1,692
More than 5 years [member] | Interests [member] |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |
Financial liabilities | € 173 | € 264

X
- Definition Undiscounted contractual values of financial assets. + References No definition available. + Details
Name: | cstm_UndiscountedContractualValuesOfFinancialAssets
Namespace Prefix: | cstm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Undiscounted contractual values of financial liabilities. + References No definition available. + Details
Name: | cstm_UndiscountedContractualValuesOfFinancialLiabilities
Namespace Prefix: | cstm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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
Name: | ifrs-full_DisclosureOfNatureAndExtentOfRisksArisingFromFinancialInstrumentsLineItems
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | ifrs-full_MaturityAxis=ifrs-full_NotLaterThanOneYearMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_ClassesOfFinancialLiabilitiesAxis=cstm_Borrowings1Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_ClassesOfFinancialLiabilitiesAxis=cstm_InterestsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_ClassesOfFinancialLiabilitiesAxis=cstm_NetDebtDerivativeLiabilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_ClassesOfFinancialLiabilitiesAxis=cstm_NetCashFlowsFromDerivativesLiabilitiesRelatedToCurrenciesAndCommoditiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_ClassesOfFinancialLiabilitiesAxis=cstm_TradePayablesAndOtherExcludingDeferredRevenueAndContractLiabilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_ClassesOfFinancialAssetsAxis=cstm_NetDebtDerivativeAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_ClassesOfFinancialAssetsAxis=cstm_NetCashFlowsFromDerivativeAssetsRelatedToCurrenciesAndCommoditiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_MaturityAxis=ifrs-full_LaterThanOneYearAndNotLaterThanFiveYearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_MaturityAxis=ifrs-full_LaterThanFiveYearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |