v3.25.1
Postretirement Benefit Plans (Funded Status and Amounts Recognized) (Details) - USD ($)
$ in Millions
Mar. 31, 2025
Mar. 31, 2024
Mar. 31, 2023
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets $ 1,257 $ 1,276  
Accrued postretirement benefits (534) (559)  
Pension Benefits [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 1,257 1,276 $ 1,275
Benefit obligation of unfunded plans (1,685) (1,719) (1,705)
Other long–term assets 11 15  
Accrued expenses and other current liabilities (19) (16)  
Accrued postretirement benefits (420) (442)  
Defined Benefit Plan, Funded (Unfunded) Status of Plan, Total (428) (443)  
Other Benefits [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Benefit obligation of unfunded plans (122) (125) $ (128)
Other long–term assets 0 0  
Accrued expenses and other current liabilities (8) (8)  
Accrued postretirement benefits (114) (117)  
Defined Benefit Plan, Funded (Unfunded) Status of Plan, Total (122) (125)  
Funded Plan [Member] | Pension Benefits [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets (112) (110)  
Benefit obligation of unfunded plans (1,369) (1,386)  
Funded Plan [Member] | Other Benefits [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 0 0  
Benefit obligation of unfunded plans 0 0  
Unfunded Plan [Member] | Pension Benefits [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Benefit obligation of unfunded plans (316) (333)  
Unfunded Plan [Member] | Other Benefits [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Benefit obligation of unfunded plans $ (122) $ (125)