XML 573 R144.htm IDEA: XBRL DOCUMENT
v3.20.4

COVID-19-RELATED GOVERNMENT ASSISTANCE (Details) € in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 EUR (€)
COVID-19 |
Government Assistance [Line Items] |
Proceeds from government assistance | € 22

X
- Definition Government Assistance + References No definition available. + Details
Name: | cstm_GovernmentAssistanceLineItems
Namespace Prefix: | cstm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Proceeds From Government Assistance, COVID-19 + References No definition available. + Details
Name: | cstm_ProceedsFromGovernmentAssistanceCOVID19
Namespace Prefix: | cstm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | cstm_UnusualOrInfrequentItemOrBoth1Axis=cstm_COVID19PandemicMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |