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PROPERTY, PLANT AND EQUIPMENT - Narrative (Details) | 12 Months Ended |
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Dec. 31, 2020 EUR (€) cash_generating_unit | Dec. 31, 2019 EUR (€) | Dec. 31, 2021 EUR (€)
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Impairment charges related to cash-generating units |  | € 0 |
Property, plant and equipment | € 1,906,000,000 | € 2,056,000,000 | € 1,948,000,000
A&T |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Expected demand percentage | 50.00% |  |
Long term growth rate used to estimate normative cash flow | 1.50% |  |
Discount rate to estimate normative cash flows | 9.00% |  |
Number of cash generating units impaired | cash_generating_unit | 2 |  |
Impairment charges related to cash-generating units | € 16,000,000 |  |
Discount rate used to estimate normative cash flow for sensitivity analysis | 20.00% |  |
Increase in discount rate that would result in the recoverable value equaling carrying amount | 2.75% |  |
Decrease in perpetual growth rate that would result in the recoverable value equaling carrying amount | 4.00% |  |
A&T | Montreuil Juigné |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Impairment charges related to cash-generating units | € 9,000,000 |  |
A&T | Ussel |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Impairment charges related to cash-generating units | € 7,000,000 |  |
AS&I |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Discount rate to estimate normative cash flows | 9.00% |  |
Number of cash generating units impaired | cash_generating_unit | 2 |  |
AS&I | Nanjing Plant |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Impairment charges related to cash-generating units | € 12,000,000 |  |
AS&I | White Georgia |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Impairment charges related to cash-generating units | 13,000,000 |  |
Property, plant and equipment | € 11,000,000 |  |

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