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, 2025
Dec. 31, 2024
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 $ 4,237 $ 4,282
Actual return on plan assets:    
Fair value of plan assets — end of year 4,346 4,237
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 145 151
OPEB    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 742 739
Actual return on plan assets:    
Fair value of plan assets — end of year 763 742
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 692 770
Actual return on plan assets:    
Relating to assets still held at the reporting date 18 18
Relating to assets sold during the period 12 7
Purchases 13 31
Sales (116) (134)
Fair value of plan assets — end of year 619 692
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 145 151
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 19  
Actual return on plan assets:    
Fair value of plan assets — end of year 15 19
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 19 27
Actual return on plan assets:    
Relating to assets still held at the reporting date 1 1
Relating to assets sold during the period 1 0
Purchases 0 0
Sales (6) (9)
Fair value of plan assets — end of year $ 15 $ 19