Annual report pursuant to Section 13 and 15(d)

PENSIONS AND POSTRETIREMENT BENEFITS - Fair Value Measurements Using Significant Unobservable Inputs (Level 3) on Changes in Plan Assets (Details)

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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, 2023
Dec. 31, 2022
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 $ 4,338 $ 5,606
Actual return on plan assets:    
Fair value of plan assets — end of year 4,282 4,338
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 143  
Actual return on plan assets:    
Fair value of plan assets — end of year 146 143
OPEB    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 728 812
Actual return on plan assets:    
Fair value of plan assets — end of year 739 728
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 912 904
Actual return on plan assets:    
Relating to assets still held at the reporting date (16) (6)
Relating to assets sold during the period 10 15
Purchases 24 28
Sales (160) (29)
Fair value of plan assets — end of year 770 912
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 143  
Actual return on plan assets:    
Fair value of plan assets — end of year 146 143
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 35  
Actual return on plan assets:    
Fair value of plan assets — end of year 27 35
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 35 42
Actual return on plan assets:    
Relating to assets still held at the reporting date 2 1
Relating to assets sold during the period 1 1
Purchases 0 0
Sales (11) (9)
Fair value of plan assets — end of year $ 27 $ 35