v3.25.1
Postretirement Benefit Plans (Components of Net Periodic Benefit Cost) (Details) - USD ($)
$ in Millions
 12 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Mar. 31, 2023
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit cost $ 0 $ 3 $ 4
Pension Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 23 23 26
Interest cost 78 76 61
Expected return on assets (80) (77) (72)
Amortization — losses (gains), net (gains (losses), net) 3 (1) 9
Amortization — prior service credit (2) (2) (2)
Settlement/curtailment (gain) loss 1 0 0
Net periodic benefit cost 23 19 22
Proportionate share of non-consolidated affiliates' pension costs 4 4 7
Total net periodic benefit cost recognized 27 23 29
Other Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 3 3 4
Interest cost 7 7 6
Expected return on assets 0 0 0
Amortization — losses (gains), net (gains (losses), net) (3) (3) (2)
Amortization — prior service credit (4) (3) (4)
Settlement/curtailment (gain) loss 0 0 0
Net periodic benefit cost 3 4 4
Proportionate share of non-consolidated affiliates' pension costs 0 0 0
Total net periodic benefit cost recognized $ 3 $ 4 $ 4