v3.25.4
Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2025
Dec. 31, 2024
Components of net periodic benefit cost for postretirement benefit plans        
Net periodic benefit cost $ 2 $ 0 $ 5 $ 1
Pension Benefit Plans        
Components of net periodic benefit cost for postretirement benefit plans        
Service cost 6 6 17 17
Interest cost 18 18 54 55
Expected return on assets (20) (20) (59) (58)
Amortization — losses (gains), net 1 2 3 3
Amortization — prior service credit, net (1) 0 (2) (1)
Settlement and curtailment gain (1) 0 (1) 0
Net periodic benefit cost 3 6 12 16
Other Benefit Plans        
Components of net periodic benefit cost for postretirement benefit plans        
Service cost 1 1 2 2
Interest cost 3 2 5 5
Expected return on assets 0 0 0 0
Amortization — losses (gains), net (1) (1) (2) (2)
Amortization — prior service credit, net (1) (1) (3) (3)
Settlement and curtailment gain 0 0 (11) 0
Net periodic benefit cost $ 2 $ 1 $ (9) $ 2