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PENSION AND POST RETIREMENT BENEFITS - Components of Accumulated Other Comprehensive Loss (Income) (Details) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Jan. 01, 2023
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service multiplier |  | $ 115 | $ 126
Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actuarial loss (gain) on benefit obligation | $ 42,000,000 | 41,000,000 |
Actual returns on assets under (over) expected | (60,000,000) | 1,165,000,000 |
Amortization of net actuarial gain (loss) | (3,000,000) | (13,000,000) |
Amortization of prior service credits (costs) | (18,000,000) | (5,000,000) |
Settlements | 4,000,000 | 8,000,000 |
Plan amendments | 3,000,000 | 122,000,000 |
OPEB |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actuarial loss (gain) on benefit obligation | (12,000,000) | (1,764,000,000) |
Actual returns on assets under (over) expected | (24,000,000) | 134,000,000 |
Amortization of net actuarial gain (loss) | 145,000,000 | 43,000,000 |
Amortization of prior service credits (costs) | 17,000,000 | 3,000,000 |
Settlements | 0 | 0 |
Plan amendments | 8,000,000 | (163,000,000) |
Discount rates | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actuarial loss (gain) on benefit obligation | 124,000,000 | (1,143,000,000) |
Discount rates | OPEB |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actuarial loss (gain) on benefit obligation | 28,000,000 | (441,000,000) |
Demographic updates | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actuarial loss (gain) on benefit obligation | (5,000,000) | (102,000,000) |
Demographic updates | OPEB |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actuarial loss (gain) on benefit obligation | (208,000,000) | (7,000,000) |
Mortality | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actuarial loss (gain) on benefit obligation | (2,000,000) | 17,000,000 |
Mortality | OPEB |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actuarial loss (gain) on benefit obligation | (11,000,000) | 0 |
Per capita healthcare costs | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actuarial loss (gain) on benefit obligation | 0 | 0 |
Per capita healthcare costs | OPEB |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actuarial loss (gain) on benefit obligation | 33,000,000 | (1,333,000,000) |
Other | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actuarial loss (gain) on benefit obligation | (1,000,000) | (8,000,000) |
Other | OPEB |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actuarial loss (gain) on benefit obligation | 0 | 0 |
Actuarial loss (gain) on benefit obligation | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actuarial loss (gain) on benefit obligation | 116,000,000 | (1,236,000,000) |
Actuarial loss (gain) on benefit obligation | OPEB |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Actuarial loss (gain) on benefit obligation | $ (158,000,000) | $ (1,781,000,000) |

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