v3.25.1
Postretirement Benefit Plans (Change in Benefit Obligation) (Details) - USD ($)
$ in Millions
 12 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Mar. 31, 2023
Pension Benefits [Member]      
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Benefit obligation at beginning of period $ 1,719 $ 1,705  
Service cost 23 23 $ 26
Interest cost 78 76 61
Members' contributions 6 6  
Benefits paid (92) (93)  
Amendments (5) 0  
Curtailments, settlements and special termination benefits (9) (10)  
Actuarial (gains) losses (31) 15  
Other (4) (4)  
Currency losses (gains) 0 1  
Benefit obligation at end of period 1,685 1,719 1,705
Other Benefits [Member]      
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Benefit obligation at beginning of period 125 128  
Service cost 3 3 4
Interest cost 7 7 6
Members' contributions 0 0  
Benefits paid (8) (9) (6)
Amendments 0 0  
Curtailments, settlements and special termination benefits 0 0  
Actuarial (gains) losses (3) (4)  
Other 0 0  
Currency losses (gains) (2) 0  
Benefit obligation at end of period 122 125 $ 128
Funded Plan [Member] | Pension Benefits [Member]      
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Benefit obligation at beginning of period 1,386    
Benefit obligation at end of period 1,369 1,386  
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 333    
Benefit obligation at end of period 316 333  
Unfunded Plan [Member] | Other Benefits [Member]      
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Benefit obligation at beginning of period 125    
Benefit obligation at end of period $ 122 $ 125