XML 112 R104.htm IDEA: XBRL DOCUMENT
v3.20.2

SHARE CAPITAL - Additional Information (Details) | Jun. 30, 2020 EUR (€) € / shares shares | Dec. 31, 2019 EUR (€) shares
--- | --- | ---
Disclosure of classes of share capital [line items] |  |
Share capital | € | € 2,758,440.64 | € 3,000,000
Nominal value of ordinary fully-paid shares (in EUR per share) | € / shares | € 0.02 |
Number of vote rights per share | 1 |
Ordinary shares |  |
Disclosure of classes of share capital [line items] |  |
Number of ordinary shares (in shares) | shares | 137,922,032 | 137,867,418

X
- Definition Number of Voting Rights Per Share + References No definition available. + Details
Name: | cstm_NumberofVotingRightsPerShare
Namespace Prefix: | cstm_
Data Type: | xbrli:integerItemType
Balance Type: | na
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_DisclosureOfClassesOfShareCapitalLineItems
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The nominal value of capital issued. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 78 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_78_e&doctype=Standard -URIDate 2019-03-27 + Details
Name: | ifrs-full_IssuedCapital
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The number of shares issued by the entity, for which full payment has been received. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 79 -Subparagraph a -Clause ii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_79_a_ii&doctype=Standard -URIDate 2019-03-27 + Details
Name: | ifrs-full_NumberOfSharesIssuedAndFullyPaid
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition The nominal value per share. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 79 -Subparagraph a -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_79_a_iii&doctype=Standard -URIDate 2019-03-27 + Details
Name: | ifrs-full_ParValuePerShare
Namespace Prefix: | ifrs-full_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | ifrs-full_ClassesOfShareCapitalAxis=ifrs-full_OrdinarySharesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |