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FINANCIAL INSTRUMENTS - Narrative (Details) - Fair value - Level 1 € in Millions | Dec. 31, 2020 EUR (€)
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Constellium SE Senior Notes Due 2024 |
Disclosure of detailed information about financial instruments [line items] |
Percentage of fair value senior notes issued | 102.00%
Senior notes issued | € 333
Constellium SE Senior Unsecured Notes Ddue 2025 |
Disclosure of detailed information about financial instruments [line items] |
Percentage of fair value senior notes issued | 102.00%
Senior notes issued | € 543
Constellium SE Senior Notes Due 2026 |
Disclosure of detailed information about financial instruments [line items] |
Percentage of fair value senior notes issued | 103.00%
Senior notes issued | € 830
Constellium SE Senir Notes Due 2028 |
Disclosure of detailed information about financial instruments [line items] |
Percentage of fair value senior notes issued | 108.00%
Senior notes issued | € 285

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