Annual report [Section 13 and 15(d), not S-K Item 405]

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, 2024
Dec. 31, 2023
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 $ 4,282 $ 4,338
Actual return on plan assets:    
Fair value of plan assets — end of year 4,237 4,282
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 146  
Actual return on plan assets:    
Fair value of plan assets — end of year 151 146
OPEB    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 739 728
Actual return on plan assets:    
Fair value of plan assets — end of year 742 739
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 770 912
Actual return on plan assets:    
Relating to assets still held at the reporting date 18 (16)
Relating to assets sold during the period 7 10
Purchases 31 24
Sales (134) (160)
Fair value of plan assets — end of year 692 770
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 146  
Actual return on plan assets:    
Fair value of plan assets — end of year 151 146
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 27  
Actual return on plan assets:    
Fair value of plan assets — end of year 19 27
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 27 35
Actual return on plan assets:    
Relating to assets still held at the reporting date 1 2
Relating to assets sold during the period 0 1
Purchases 0 0
Sales (9) (11)
Fair value of plan assets — end of year $ 19 $ 27