XML 554 R125.htm IDEA: XBRL DOCUMENT v3.20.4

FINANCIAL RISK MANAGEMENT - Impact on Profit and Equity (Before Tax Effect) of a 10% Strengthening of US Dollar Versus Euro for US Dollar Functional Currency Entities (Details) - 10% strengthening U.S. Dollar/Euro € in Millions	12 Months Ended
	Dec. 31, 2020 EUR (€)
Disclosure of nature and extent of risks arising from financial instruments [line items]
Effect on profit before tax	€ 3
Effect on pretax equity	€ 30

X

- Definition

Foreign exchange sensitivity effect on pretax equity.

+ References

No definition available.

+ Details

Name:	cstm_ForeignExchangeSensitivityEffectOnPretaxEquity
Namespace Prefix:	cstm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Foreign exchange sensitivity effect on profit before tax.

+ References

No definition available.

+ Details

Name:	cstm_ForeignExchangeSensitivityEffectOnProfitBeforeTax
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

- Details

Name:	cstm_SensitivityAnalysisAxis=cstm_TenPercentageStrengtheningUsDollarEuroMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: