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TRADE RECEIVABLES AND OTHER - Narrative (Details) | 12 Months Ended
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Dec. 31, 2020 EUR (€) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 EUR (€)
Disclosure of trade and other receivables [line items] |  |  |
Allowance for impairment on trade receivables recognized | € 1,900,000 |  | € 400,000
Trade receivables | 341,000,000 |  | 393,000,000
Total factored assets | 514,000,000 |  | 574,000,000
Factored assets derecognized | 398,000,000 |  | 463,000,000
Debt due factor | 0 |  | 0
Impairment |  |  |
Disclosure of trade and other receivables [line items] |  |  |
Trade receivables | 0 |  | € 0
United States | Factoring of receivables | Muscle Shoals factoring facility |  |  |
Disclosure of trade and other receivables [line items] |  |  |
Factoring maximum capacity | $ |  | $ 300,000,000 |
United States | Factoring of receivables | Constellium automotive |  |  |
Disclosure of trade and other receivables [line items] |  |  |
Factoring maximum capacity | $ |  | $ 25,000,000 |
France | Factoring of receivables |  |  |
Disclosure of trade and other receivables [line items] |  |  |
Factoring maximum capacity | 255,000,000 |  |
France | Factoring Receivable, Recourse Line |  |  |
Disclosure of trade and other receivables [line items] |  |  |
Factoring maximum capacity | 20,000,000 |  |
Germany, Switzerland and Czech Republic | Factoring of receivables |  |  |
Disclosure of trade and other receivables [line items] |  |  |
Factoring maximum capacity | € 150,000,000 |  |

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- Definition The amount of impairment loss or reversal of impairment loss recognised in profit or loss for trade receivables. [Refer: Impairment loss recognised in profit or loss; Reversal of impairment loss recognised in profit or loss; Trade receivables] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_112_c&doctype=Standard -URIDate 2020-01-01 + Details
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