v3.26.1
Postretirement Benefit Plans (Pension Plan Obligations) (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Defined Benefit Pension Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Benefit Obligation $ 1,577 $ 1,685 $ 1,719
Defined Benefit Plan, Accumulated Benefit Obligation 1,523 1,615  
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Plan Assets 1,053 1,152  
Pension plans with accumulated benefit obligations in excess of plan assets, accumulated benefit obligation 1,401 1,520  
Other Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation 1,457 1,591  
Pension plans with accumulated benefit obligations in excess of plan assets, fair value of plan assets 1,042 1,141  
Pension plans with accumulated benefit obligations in excess of plan assets, projected benefit obligation 120 94  
Pension plans with accumulated benefit obligations in excess of plan assets, fair value of plan assets $ 138 $ 105