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PENSIONS AND POSTRETIREMENT BENEFITS - Fair Value Measurements Using Significant Unobservable Inputs (Level 3) on Changes in Plan Assets (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2022 | Dec. 31, 2021
Pension Benefits |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward] |  |
Fair value of plan assets — beginning of year | $ 5,606 | $ 5,332
Actual return on plan assets: |  |
Fair value of plan assets — end of year | 4,338 | 5,606
Pension Benefits | Private equity |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward] |  |
Fair value of plan assets — beginning of year | 151 |
Actual return on plan assets: |  |
Fair value of plan assets — end of year | 143 | 151
Reserve for investment commitments | 117 |
OPEB |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward] |  |
Fair value of plan assets — beginning of year | 812 | 783
Actual return on plan assets: |  |
Fair value of plan assets — end of year | 728 | 812
OPEB | Private equity |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward] |  |
Fair value of plan assets — beginning of year | 0 |
Actual return on plan assets: |  |
Fair value of plan assets — end of year | 0 | 0
Significant Unobservable Inputs (Level 3) | Pension Benefits |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward] |  |
Fair value of plan assets — beginning of year | 904 | 670
Actual return on plan assets: |  |
Relating to assets still held at the reporting date | (6) | 124
Relating to assets sold during the period | 15 | 8
Purchases | 28 | 142
Sales | (29) | (40)
Acquired through business combinations | 0 |
Fair value of plan assets — end of year | 912 | 904
Significant Unobservable Inputs (Level 3) | Pension Benefits | Private equity |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward] |  |
Fair value of plan assets — beginning of year | 151 |
Actual return on plan assets: |  |
Fair value of plan assets — end of year | 143 | 151
Significant Unobservable Inputs (Level 3) | OPEB |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward] |  |
Fair value of plan assets — beginning of year | 42 |
Actual return on plan assets: |  |
Fair value of plan assets — end of year | 35 | 42
Significant Unobservable Inputs (Level 3) | OPEB | Private equity |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward] |  |
Fair value of plan assets — beginning of year | 0 |
Actual return on plan assets: |  |
Fair value of plan assets — end of year | 0 | 0
Significant Unobservable Inputs (Level 3) | OPEB | VEBA Assets |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward] |  |
Fair value of plan assets — beginning of year | 42 | 38
Actual return on plan assets: |  |
Relating to assets still held at the reporting date | 1 | 6
Relating to assets sold during the period | 1 | 0
Purchases | 0 | 0
Sales | (9) | (2)
Fair value of plan assets — end of year | $ 35 | $ 42

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