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FINANCIAL RISK MANAGEMENT - Narrative (Details) SFr in Millions, $ in Millions | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Dec. 31, 2020 EUR (€) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 EUR (€) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Jun. 30, 2019 CHF (SFr) | Dec. 31, 2018 EUR (€) | Dec. 31, 2017 EUR (€)
Disclosure of liquidity risk [line items] |  |  |  |  |  |  |  |
Percentage of trade account receivables insured | 82.00% |  |  | 82.00% |  |  |  |
Revolving credit facilities outstanding availability | € 514,000,000 |  |  |  |  |  |  |
Liquidity value | 981,000,000 |  |  |  |  |  |  |
Cash and cash equivalents | 439,000,000 |  | € 184,000,000 |  |  |  | € 164,000,000 | € 269,000,000
Undrawn facilities | 542,000,000 |  |  |  |  |  |  |
Forward contract |  |  |  |  |  |  |  |
Disclosure of liquidity risk [line items] |  |  |  |  |  |  |  |
Total nominal amount forward contracts | SFr |  |  |  |  |  | SFr 174 |  |
Unrealized loss of the net investment hedge | 3,000,000 |  |  |  |  |  |  |
Derivative classified as cash flow hedge |  |  |  |  |  |  |  |
Disclosure of liquidity risk [line items] |  |  |  |  |  |  |  |
Nominal amount hedging instrument | $ |  |  |  | $ 330 | $ 233 |  |  |
Forward purchase contracts versus EURO |  |  |  |  |  |  |  |
Disclosure of liquidity risk [line items] |  |  |  |  |  |  |  |
Net position hedges related to loans and deposits | $ |  | $ 518 |  |  |  |  |  |
Forward purchase contracts versus EURO | Foreign exchange forward contracts |  |  |  |  |  |  |  |
Disclosure of liquidity risk [line items] |  |  |  |  |  |  |  |
Net position hedges related to loans and deposits | $ |  | 47 |  |  |  |  |  |
Forward purchase contracts versus EURO | Cross currency swaps |  |  |  |  |  |  |  |
Disclosure of liquidity risk [line items] |  |  |  |  |  |  |  |
Net position hedges related to loans and deposits | $ |  | $ 565 |  |  |  |  |  |
U.S. Revolving Facility |  |  |  |  |  |  |  |
Disclosure of liquidity risk [line items] |  |  |  |  |  |  |  |
Borrowing base | $ |  |  |  | 396 |  |  |  |
French Inventory Based Facility |  |  |  |  |  |  |  |
Disclosure of liquidity risk [line items] |  |  |  |  |  |  |  |
Borrowing base | $ |  |  |  | 74 |  |  |  |
German Facility |  |  |  |  |  |  |  |
Disclosure of liquidity risk [line items] |  |  |  |  |  |  |  |
Borrowing base | $ |  |  |  | $ 50 |  |  |  |
Currency risk |  |  |  |  |  |  |  |
Disclosure of liquidity risk [line items] |  |  |  |  |  |  |  |
Margin requirement paid as collateral to counterparties | 3,000,000 |  |  |  |  |  |  |
Commodity price risk |  |  |  |  |  |  |  |
Disclosure of liquidity risk [line items] |  |  |  |  |  |  |  |
Margin requirement for aluminum and other commodity hedges | 0 |  | 0 |  |  |  |  |
10% increase or decrease in the market price | Aluminium |  |  |  |  |  |  |  |
Disclosure of liquidity risk [line items] |  |  |  |  |  |  |  |
Impact of increase or decrease in market price in gain or loss from derivatives | 27,000,000 |  |  |  |  |  |  |
Top of range | 50 basis point increase or decrease in the LIBOR or EURIBOR interest rates |  |  |  |  |  |  |  |
Disclosure of liquidity risk [line items] |  |  |  |  |  |  |  |
Impact of increase or decrease in interest rate in income before income tax | € 1,000,000 |  | € 1,000,000 |  |  |  |  |

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