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PENSIONS AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS - Movement in Net Defined Benefit Obligations (Details) € in Millions, $ in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended
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Jun. 30, 2020 EUR (€) | Jun. 30, 2019 EUR (€) | Jun. 30, 2020 EUR (€) | Jun. 30, 2020 USD ($) | Jun. 30, 2019 EUR (€) | Dec. 31, 2019 EUR (€) | Dec. 31, 2018 EUR (€)
Disclosure of net defined benefit liability (asset) [line items] |  |  |  |  |  |  |
Beginning balance |  |  | € 670 | $ 670 |  |  |
Remeasurements due to: |  |  |  |  |  |  |
Closing balance | € 715 |  | 715 |  |  | € 670 |
Included in the Unaudited Interim Consolidated Income Statement |  |  |  |  |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |  |  |  |  |
Current service cost | 6 | € 6 | 14 |  | € 12 |  |
Interest cost / (income) | 3 | 4 | 6 |  | 8 |  |
Past service cost | 2 | 0 | 2 |  | 0 |  |
Immediate recognition of gains / (losses) arising over the year | 1 | 2 | 0 |  | 2 |  |
Administration expenses | 1 | 0 | 1 |  | 1 |  |
Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss) |  |  |  |  |  |  |
Remeasurements due to: |  |  |  |  |  |  |
—actual return less interest on plan assets |  |  | 13 |  |  |  |
—changes in financial assumptions |  |  | 27 |  |  |  |
—changes in demographic assumptions |  |  | 0 |  |  |  |
—experience losses |  |  | 0 |  |  |  |
Effects of changes in foreign exchange rates |  |  | 2 |  |  |  |
Included in the Unaudited Interim Consolidated Statement of Cash Flows |  |  |  |  |  |  |
Remeasurements due to: |  |  |  |  |  |  |
Benefits paid |  |  | (10) |  |  |  |
Contributions by the Group |  |  | (10) |  |  |  |
Contributions by the plan participants |  |  | 0 |  |  |  |
Pension Benefits | Included in the Unaudited Interim Consolidated Income Statement |  |  |  |  |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |  |  |  |  |
Current service cost | 5 | 5 | 11 |  | 9 |  |
Interest cost / (income) | 2 | 2 | 3 |  | 4 |  |
Past service cost | 0 | 0 | 0 |  | 0 |  |
Immediate recognition of gains / (losses) arising over the year | 0 | 0 | 0 |  | 0 |  |
Administration expenses | 1 | 0 | 1 |  | 1 |  |
Other Benefits |  |  |  |  |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |  |  |  |  |
Past service cost |  |  | 2 |  |  | 3 | € 36
Other Benefits | Included in the Unaudited Interim Consolidated Income Statement |  |  |  |  |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |  |  |  |  |
Current service cost | 1 | 1 | 3 |  | 3 |  |
Interest cost / (income) | 1 | 2 | 3 |  | 4 |  |
Past service cost | 2 | 0 | 2 |  | 0 |  |
Immediate recognition of gains / (losses) arising over the year | 1 | 2 | 0 |  | 2 |  |
Administration expenses | 0 | € 0 | 0 |  | € 0 |  |
Defined benefit obligations |  |  |  |  |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |  |  |  |  |
Beginning balance |  |  | 1,115 |  |  |  |
Remeasurements due to: |  |  |  |  |  |  |
Closing balance | 1,150 |  | 1,150 |  |  | 1,115 |
Defined benefit obligations | Included in the Unaudited Interim Consolidated Income Statement |  |  |  |  |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |  |  |  |  |
Current service cost |  |  | 14 |  |  |  |
Interest cost / (income) |  |  | 10 |  |  |  |
Past service cost |  |  | 2 |  |  |  |
Immediate recognition of gains / (losses) arising over the year |  |  | 0 |  |  |  |
Administration expenses |  |  | 0 |  |  |  |
Defined benefit obligations | Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss) |  |  |  |  |  |  |
Remeasurements due to: |  |  |  |  |  |  |
—actual return less interest on plan assets |  |  | 0 |  |  |  |
—changes in financial assumptions |  |  | 27 |  |  |  |
—changes in demographic assumptions |  |  | 0 |  |  |  |
—experience losses |  |  | 0 |  |  |  |
Effects of changes in foreign exchange rates |  |  | 7 |  |  |  |
Defined benefit obligations | Included in the Unaudited Interim Consolidated Statement of Cash Flows |  |  |  |  |  |  |
Remeasurements due to: |  |  |  |  |  |  |
Benefits paid |  |  | (27) |  |  |  |
Contributions by the Group |  |  | 0 |  |  |  |
Contributions by the plan participants |  |  | 2 |  |  |  |
Defined benefit obligations | Pension Benefits |  |  |  |  |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |  |  |  |  |
Beginning balance |  |  | 895 |  |  |  |
Remeasurements due to: |  |  |  |  |  |  |
Closing balance | 920 |  | 920 |  |  | 895 |
Defined benefit obligations | Pension Benefits | Included in the Unaudited Interim Consolidated Income Statement |  |  |  |  |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |  |  |  |  |
Current service cost |  |  | 11 |  |  |  |
Interest cost / (income) |  |  | 7 |  |  |  |
Past service cost |  |  | 0 |  |  |  |
Immediate recognition of gains / (losses) arising over the year |  |  | 0 |  |  |  |
Administration expenses |  |  | 0 |  |  |  |
Defined benefit obligations | Pension Benefits | Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss) |  |  |  |  |  |  |
Remeasurements due to: |  |  |  |  |  |  |
—actual return less interest on plan assets |  |  | 0 |  |  |  |
—changes in financial assumptions |  |  | 16 |  |  |  |
—changes in demographic assumptions |  |  | 0 |  |  |  |
—experience losses |  |  | 1 |  |  |  |
Effects of changes in foreign exchange rates |  |  | 6 |  |  |  |
Defined benefit obligations | Pension Benefits | Included in the Unaudited Interim Consolidated Statement of Cash Flows |  |  |  |  |  |  |
Remeasurements due to: |  |  |  |  |  |  |
Benefits paid |  |  | (18) |  |  |  |
Contributions by the Group |  |  | 0 |  |  |  |
Contributions by the plan participants |  |  | 2 |  |  |  |
Defined benefit obligations | Other Benefits |  |  |  |  |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |  |  |  |  |
Beginning balance |  |  | 220 |  |  |  |
Remeasurements due to: |  |  |  |  |  |  |
Closing balance | 230 |  | 230 |  |  | 220 |
Defined benefit obligations | Other Benefits | Included in the Unaudited Interim Consolidated Income Statement |  |  |  |  |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |  |  |  |  |
Current service cost |  |  | 3 |  |  |  |
Interest cost / (income) |  |  | 3 |  |  |  |
Past service cost |  |  | 2 |  |  |  |
Immediate recognition of gains / (losses) arising over the year |  |  | 0 |  |  |  |
Administration expenses |  |  | 0 |  |  |  |
Defined benefit obligations | Other Benefits | Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss) |  |  |  |  |  |  |
Remeasurements due to: |  |  |  |  |  |  |
—actual return less interest on plan assets |  |  | 0 |  |  |  |
—changes in financial assumptions |  |  | 11 |  |  |  |
—changes in demographic assumptions |  |  | 0 |  |  |  |
—experience losses |  |  | (1) |  |  |  |
Effects of changes in foreign exchange rates |  |  | 1 |  |  |  |
Defined benefit obligations | Other Benefits | Included in the Unaudited Interim Consolidated Statement of Cash Flows |  |  |  |  |  |  |
Remeasurements due to: |  |  |  |  |  |  |
Benefits paid |  |  | (9) |  |  |  |
Contributions by the Group |  |  | 0 |  |  |  |
Contributions by the plan participants |  |  | 0 |  |  |  |
Plan Assets |  |  |  |  |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |  |  |  |  |
Beginning balance |  |  | (445) |  |  |  |
Remeasurements due to: |  |  |  |  |  |  |
Closing balance | € (435) |  | (435) |  |  | € (445) |
Plan Assets | Included in the Unaudited Interim Consolidated Income Statement |  |  |  |  |  |  |
Disclosure of net defined benefit liability (asset) [line items] |  |  |  |  |  |  |
Current service cost |  |  | 0 |  |  |  |
Interest cost / (income) |  |  | (4) |  |  |  |
Past service cost |  |  | 0 |  |  |  |
Immediate recognition of gains / (losses) arising over the year |  |  | 0 |  |  |  |
Administration expenses |  |  | 1 |  |  |  |
Plan Assets | Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss) |  |  |  |  |  |  |
Remeasurements due to: |  |  |  |  |  |  |
—actual return less interest on plan assets |  |  | 13 |  |  |  |
—changes in financial assumptions |  |  | 0 |  |  |  |
—changes in demographic assumptions |  |  | 0 |  |  |  |
—experience losses |  |  | 0 |  |  |  |
Effects of changes in foreign exchange rates |  |  | (5) |  |  |  |
Plan Assets | Included in the Unaudited Interim Consolidated Statement of Cash Flows |  |  |  |  |  |  |
Remeasurements due to: |  |  |  |  |  |  |
Benefits paid |  |  | 17 |  |  |  |
Contributions by the Group |  |  | (10) |  |  |  |
Contributions by the plan participants |  |  | € (2) |  |  |  |

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- Definition The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in demographic assumptions that result in remeasurements of the net defined benefit liability (asset). Demographic assumptions deal with matters such as: (a) mortality; (b) rates of employee turnover, disability and early retirement; (c) the proportion of plan members with dependants who will be eligible for benefits; (d) the proportion of plan members who will select each form of payment option available under the plan terms; and (e) claim rates under medical plans. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 141 -Subparagraph c -Clause ii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_141_c_ii&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in financial assumptions that result in remeasurements of the net defined benefit liability (asset). Financial assumptions deal with items such as: (a) the discount rate; (b) benefit levels, excluding any cost of the benefits to be met by employees, and future salary; (c) in the case of medical benefits, future medical costs, including claim handling costs (ie the costs that will be incurred in processing and resolving claims, including legal and adjuster's fees); and (d) taxes payable by the plan on contributions relating to service before the reporting date or on benefits resulting from that service. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 141 -Subparagraph c -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_141_c_iii&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The increase (decrease) in the net defined benefit liability (asset) resulting from employee service in the current period. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 141 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_141_a&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The increase (decrease) in the net defined benefit liability (asset) resulting from changes in foreign exchange rates. [Refer: Net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 141 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_141_e&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The decrease (increase) in the net defined benefit liability (asset) resulting from the return on plan assets, excluding amounts included in interest income or expense. The return on plans assets is interest, dividends and other revenue derived from the plan assets, together with realised and unrealised gains or losses on the plan assets, less any costs of managing plan assets and less any tax payable by the plan itself, other than tax included in the actuarial assumptions used to measure the present value of the defined benefit obligation. [Refer: Plan assets [member]; Net defined benefit liability (asset); Actuarial assumptions [member]; Interest expense (income), net defined benefit liability (asset)] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 141 -Subparagraph c -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_141_c_i&doctype=Standard -URIDate 2019-03-27 + Details
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