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RELATED PARTIES - Narrative (Details) - EUR (€) € in Millions | Mar. 28, 2018 | Dec. 31, 2021 | Dec. 31, 2020 | May 13, 2020 | Dec. 31, 2019
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Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Borrowings |  | € 2,129 | € 2,391 |  | € 2,361
Secured French PGE French Facility (due 2022) |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Borrowings |  | 180 | 180 |  |
Secured French PGE French Facility (due 2022) | French Government |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Borrowings |  |  |  | € 180 |
Percentage of borrowings guaranteed |  |  |  | 80.00% |
Secured French PGE French Facility (due 2022) | French Government | BPI France |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Borrowings |  |  |  | € 30 |
Unsecured Revolving Credit Facility (expired in 2021) |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Borrowings |  | € 0 | € 0 |  |
Unsecured Revolving Credit Facility (expired in 2021) | BPI France |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Term of credit facility | 3 years |  |  |  |
Borrowing capacity | € 10 |  |  |  |

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