Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2025	Dec. 31, 2024
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning of period	$ 996	$ 1,201	$ 1,003	$ 1,047
OCI, before reclassifications and income taxes	(2)	6	(2)	(1)
Income taxes	1	(2)	1	0
OCI before reclassifications, net of income taxes	(1)	4	(1)	(1)
Amounts reclassified from AOCI to earnings, before income taxes	0	(1)	(1)	(8)
Income taxes	0	0	0	2
Amounts reclassified from AOCI to earnings, net of income taxes	0	(1)	(1)	(6)
Current-period OCI, net of income taxes	(1)	3	(2)	(7)
End of period	1,025	1,210	1,025	1,210
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning of period	(30)	0	(29)	10
End of period	(31)	3	(31)	3
Post-retirement plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning of period	(27)	2	(28)	2
OCI, before reclassifications and income taxes	(2)	0	(2)	0
Income taxes	1	0	1	0
OCI before reclassifications, net of income taxes	(1)	0	(1)	0
Amounts reclassified from AOCI to earnings, before income taxes	0	0	1	0
Income taxes	0	0	0	0
Amounts reclassified from AOCI to earnings, net of income taxes	0	0	1	0
Current-period OCI, net of income taxes	(1)	0	0	0
End of period	(28)	2	(28)	2
Derivatives designated as cash flow hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning of period	(3)	(2)	(1)	8
OCI, before reclassifications and income taxes	0	6	0	(1)
Income taxes	0	(2)	0	0
OCI before reclassifications, net of income taxes	0	4	0	(1)
Amounts reclassified from AOCI to earnings, before income taxes	0	(1)	(2)	(8)
Income taxes	0	0	0	2
Amounts reclassified from AOCI to earnings, net of income taxes	0	(1)	(2)	(6)
Current-period OCI, net of income taxes	0	3	(2)	(7)
End of period	$ (3)	$ 1	$ (3)	$ 1