XML 102 R94.htm IDEA: XBRL DOCUMENT
v3.20.2

FINANCIAL RISK MANAGEMENT - Effect of Foreign Currency Derivatives Impacts and Commercial Transactions Exposures (Details) - EUR (€) € in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |  |
Realized gains / (losses) on foreign currency derivatives - net | € (3) | € 0 | € (3) | € 1
Unrealized gains / (losses) on foreign currency derivatives - net | 0 | (1) | (2) | 1
Losses reclassified from OCI as a result of hedge accounting discontinuation | (5) | 0 | (5) | 0
Included in Other gains / (losses) - net |  |  |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |  |
Losses reclassified from OCI as a result of hedge accounting discontinuation | (5) | 0 | (5) | 0
Derivatives that do not qualify for hedge accounting | Included in Other gains / (losses) - net |  |  |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |  |
Realized gains / (losses) on foreign currency derivatives - net | 0 | 1 | 2 | 3
Unrealized gains / (losses) on foreign currency derivatives - net | (1) | (1) | (2) | 1
Derivatives that qualify for hedge accounting | Included in Revenue |  |  |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |  |
Realized gains / (losses) on foreign currency derivatives - net | (3) | (1) | (5) | (2)
Unrealized gains / (losses) on foreign currency derivatives - net | 1 | 0 | 0 | 0
Derivatives that qualify for hedge accounting | Included in Other comprehensive income / (loss) |  |  |  |
Disclosure of nature and extent of risks arising from financial instruments [line items] |  |  |  |
Unrealized gains / (losses) on foreign currency derivatives - net | 2 | 1 | (6) | (7)
Gains reclassified from cash flow hedge reserve to the Unaudited Interim Consolidated Income Statement | € 3 | € 1 | € 6 | € 2

X
- Definition (Gains) Losses recognized on reclassification adjustments on cash flow hedges. + References No definition available. + Details
Name: | cstm_GainsLossesRecognizedOnReclassificationAdjustmentsOnCashFlowHedges
Namespace Prefix: | cstm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Realized gains (losses) on foreign currency derivatives - net. + References No definition available. + Details
Name: | cstm_RealizedGainsLossesOnForeignCurrencyDerivativesNet
Namespace Prefix: | cstm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Unrealized gains (losses) on foreign currency derivatives - net. + References No definition available. + Details
Name: | cstm_UnrealizedGainsLossesOnForeignCurrencyDerivativesNet
Namespace Prefix: | cstm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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
- Definition The gain (loss) recognised in profit or loss on hedge ineffectiveness. [Refer: Gain (loss) on hedge ineffectiveness] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph 24C -Subparagraph a -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_24C_a_i&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph 24C -Subparagraph b -Clause ii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_24C_b_ii&doctype=Standard -URIDate 2019-03-27 + Details
Name: | ifrs-full_GainLossOnHedgeIneffectivenessRecognisedInProfitOrLoss
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | ifrs-full_ConsolidatedAndSeparateFinancialStatementsAxis=cstm_OtherGainsAndLossesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | cstm_DerivativeInstrumentAxis=cstm_NonqualifyingHedgesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | cstm_DerivativeInstrumentAxis=cstm_QualifyingHedgesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_ConsolidatedAndSeparateFinancialStatementsAxis=cstm_RevenueFromContractWithCustomersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_ConsolidatedAndSeparateFinancialStatementsAxis=cstm_OtherComprehensiveIncomeLossMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |