Annual report pursuant to Section 13 and 15(d)

PENSION AND OTHER POSTRETIREMENT BENEFITS - (Details 5 ) - Level 3 Fair Value Reconciliation

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PENSION AND OTHER POSTRETIREMENT BENEFITS - (Details 5 ) - Level 3 Fair Value Reconciliation - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
UNITED STATES      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets $ 3,826 $ 3,828 $ 3,548
UNITED STATES | Fair Value, Inputs, Level 3      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 604 641 551
Unrealized gains (losses) on assets still held at the reporting date (7) 25  
Purchases, sales and settlements, net (30) (29)  
Assumption of Meritor's plan assets   94  
UNITED STATES | Fair Value, Inputs, Level 3 | Private Markets      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 537 559 471
Unrealized gains (losses) on assets still held at the reporting date 6 6  
Purchases, sales and settlements, net (28) (12)  
Assumption of Meritor's plan assets   94  
UNITED STATES | Fair Value, Inputs, Level 3 | Real Assets      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 67 82 80
Unrealized gains (losses) on assets still held at the reporting date (13) 19  
Purchases, sales and settlements, net (2) (17)  
Assumption of Meritor's plan assets   0  
UNITED KINGDOM      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 1,720 1,670 2,390
UNITED KINGDOM | Insurance      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 436 428  
UNITED KINGDOM | Fair Value, Inputs, Level 3      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 539 818 903
Unrealized gains (losses) on assets still held at the reporting date (27) (141)  
Purchases, sales and settlements, net (252) (36)  
Assumption of Meritor's plan assets   92  
UNITED KINGDOM | Fair Value, Inputs, Level 3 | Private Markets      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 96 382 356
Unrealized gains (losses) on assets still held at the reporting date (35) 39  
Purchases, sales and settlements, net (251) (13)  
Assumption of Meritor's plan assets   0  
UNITED KINGDOM | Fair Value, Inputs, Level 3 | Real Assets      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 7 8 33
Unrealized gains (losses) on assets still held at the reporting date 0 (2)  
Purchases, sales and settlements, net (1) (23)  
Assumption of Meritor's plan assets   0  
UNITED KINGDOM | Fair Value, Inputs, Level 3 | Insurance      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 436 428 $ 514
Unrealized gains (losses) on assets still held at the reporting date 8 (178)  
Purchases, sales and settlements, net $ 0 0  
Assumption of Meritor's plan assets   $ 92