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PENSIONS AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS - Narrative (Details) - EUR (€) € in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2020 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2020 | Dec. 31, 2019
Disclosure of defined benefit plans [line items] |  |  |  |  |
Reduction in defined benefit liability for negative past service costs |  |  | € 36 | € (2) | € 1
Weighted-average maturity of defined benefit obligations |  |  |  | 14 years 2 months 12 days | 14 years 1 month 6 days
Pension Benefits |  |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |  |
Expected contributions to pension and other benefits for next year |  |  |  | € 24 |
Other Benefits |  |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |  |
Reduction in defined benefit liability for negative past service costs | € 3 | € 2 |  | 2 |
Expected contributions to pension and other benefits for next year |  |  |  | € 15 |
Actuarial assumption of discount rates |  |  |  |  |
Disclosure of defined benefit plans [line items] |  |  |  |  |
Increase in actuarial assumption | 0.50% |  |  | 0.50% |

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- Definition Weighted-average maturity of defined benefit obligations. + References No definition available. + Details
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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
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- Definition The estimate of the expected contributions to be made to a defined benefit plan for the next annual reporting period. [Refer: Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 147 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_147_b&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 148 -Subparagraph d -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_148_d_iii&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition The increase (decrease) in the net defined benefit liability (asset) resulting from past service cost. Past service cost is the change in the present value of the defined benefit obligation for employee service in prior periods, resulting from a plan amendment (the introduction or withdrawal of, or changes to, a defined benefit plan) or a curtailment (a significant reduction by the entity in the number of employees covered by a plan). [Refer: Net defined benefit liability (asset); Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 141 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_141_d&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition The reasonably possible percentage of the increase in the actuarial assumption used to determine the present value of defined benefit obligation. [Refer: Actuarial assumptions [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 145 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_145_a&doctype=Standard -URIDate 2020-01-01 + Details
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