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PENSIONS AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS - Actuarial Assumptions (Details) | Dec. 31, 2020 | Dec. 31, 2019
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OPEB | Pre 65 | 2020 |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Medical trend rate | 6.25% |
OPEB | Pre 65 | 2029 |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Medical trend rate | 4.50% |
OPEB | Post 65 | 2020 |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Medical trend rate | 6.00% |
OPEB | Post 65 | 2029 |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Medical trend rate | 4.50% |
Switzerland |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Rate of increase in salaries | 1.50% | 1.50%
Rate of increase in pensions | 0.00% | 0.00%
Discount rate | 0.00% | 0.15%
U.S. |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Rate of increase in salaries | 0.00% | 0.00%
Rate of increase in pensions | 0.00% | 0.00%
Discount rate | 0.00% | 0.00%
U.S. | Hourly pension |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Rate of increase in salaries | 2.20% | 2.20%
Rate of increase in pensions | 0.00% | 0.00%
U.S. | Hourly pension | Bottom of range |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Discount rate | 2.45% | 3.15%
U.S. | Hourly pension | Top of range |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Discount rate | 2.65% | 3.25%
U.S. | Salaried pension |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Rate of increase in salaries | 3.80% | 3.80%
Rate of increase in pensions | 0.00% | 0.00%
Discount rate | 2.55% | 3.25%
U.S. | OPEB |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Rate of increase in salaries | 3.80% | 3.80%
Rate of increase in pensions | 0.00% | 0.00%
U.S. | OPEB | Bottom of range |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Discount rate | 2.50% | 3.20%
U.S. | OPEB | Top of range |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Discount rate | 2.80% | 3.40%
U.S. | Other benefits |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Rate of increase in salaries | 3.80% | 3.80%
Rate of increase in pensions | 0.00% | 0.00%
U.S. | Other benefits | Bottom of range |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Discount rate | 2.20% | 3.00%
U.S. | Other benefits | Top of range |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Discount rate | 2.55% | 3.20%
France |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Rate of increase in pensions | 2.00% | 2.00%
Discount rate | 0.00% | 0.00%
France | Bottom of range |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Rate of increase in salaries | 1.50% | 1.50%
France | Top of range |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Rate of increase in salaries | 3.50% | 3.50%
France | Retirements |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Rate of increase in salaries | 0.00% | 0.00%
Rate of increase in pensions | 0.00% | 0.00%
Discount rate | 0.50% | 0.95%
France | Other benefits |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Rate of increase in salaries | 0.00% | 0.00%
Rate of increase in pensions | 0.00% | 0.00%
Discount rate | 0.40% | 0.80%
Germany |  |
Disclosure of sensitivity analysis for actuarial assumptions [line items] |  |
Rate of increase in salaries | 2.50% | 2.75%
Rate of increase in pensions | 1.50% | 1.70%
Discount rate | 0.55% | 1.00%

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- Definition The discount rate used as the significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit obligation, at present value; Actuarial assumptions [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 144 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_144&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition The expected rate of increases in pension that is used as a significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit plans [member]; Defined benefit obligation, at present value; Actuarial assumptions [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 144 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_144&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition Medical cost trend rate used as significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit obligation, at present value; Actuarial assumptions [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 144 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_144&doctype=Standard -URIDate 2020-01-01 + Details
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