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PENSION AND OTHER POST-EMPLOYEMENT BENEFITS - Schedule of Assumed Rate of Return on Pension Plan Assets Considers Historical Market Returns and Economic Forecasts (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Pensions and OPEB |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actual gains or (losses) on plan assets - $ millions | $ 751 | $ (1,830) | $ 689
Actual gains or (losses) on plan assets - % | 11.20% | (19.10%) | 7.90%
Expected return on plan assets - $ millions | $ 601 | $ 696 | $ 688
Expected return on plan assets |  | 7.50% | 7.50%
Pension |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actual gains or (losses) on plan assets - $ millions | 682 | $ (1,760) |
Expected return on plan assets - $ millions | $ 570 | $ 657 | $ 652
Expected return on plan assets | 8.00% | 7.50% | 7.50%
OPEB |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actual gains or (losses) on plan assets - $ millions | $ 69 | $ (70) |
Expected return on plan assets - $ millions | $ 31 | $ 39 | $ 36
Expected return on plan assets | 7.00% | 7.50% | 7.50%

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- Definition Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-8 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(3) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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