v3.26.1
Postretirement Benefit Plans (Change in Benefit Obligation) (Details) - USD ($)
$ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Pension Benefits [Member]      
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Benefit obligation at beginning of period $ 1,685 $ 1,719  
Service cost 24 23 $ 23
Interest cost 71 78 76
Members' contributions 6 6  
Benefits paid (98) (92)  
Amendments 1 (5)  
Curtailments, settlements and special termination benefits (117) (9)  
Actuarial gains (39) (31)  
Other (5) (4)  
Currency losses (gains) 49 0  
Benefit obligation at end of period 1,577 1,685 1,719
Other Benefits [Member]      
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Benefit obligation at beginning of period 122 125  
Service cost 2 3 3
Interest cost 7 7 7
Members' contributions 0 0  
Benefits paid (9) (8) (9)
Amendments 0 0  
Curtailments, settlements and special termination benefits (6) 0  
Actuarial gains (10) (3)  
Other 0 0  
Currency losses (gains) 1 (2)  
Benefit obligation at end of period 107 122 $ 125
Funded Plan [Member] | Pension Benefits [Member]      
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Benefit obligation at beginning of period 1,369    
Benefit obligation at end of period 1,271 1,369  
Funded Plan [Member] | Other Benefits [Member]      
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Benefit obligation at beginning of period 0    
Benefit obligation at end of period 0 0  
Unfunded Plan [Member] | Pension Benefits [Member]      
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Benefit obligation at beginning of period 316    
Benefit obligation at end of period 306 316  
Unfunded Plan [Member] | Other Benefits [Member]      
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Benefit obligation at beginning of period 122    
Benefit obligation at end of period $ 107 $ 122