Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
Jun. 30, 2025	Jun. 30, 2024
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning of period	$ 1,003	$ 1,047
OCI, before reclassifications to earnings and income taxes		1
Income taxes		0
OCI before reclassifications to earnings, net of income taxes		1
Amounts reclassified from AOCI to earnings, before income taxes	(1)	(4)
Income taxes	0	1
Amounts reclassified from AOCI to earnings, net of income taxes	(1)	(3)
Current-period OCI, net of income taxes	(1)	(2)
End of period	1,065	1,084
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning of period	(29)	10
End of period	(30)	8
Post-retirement plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning of period	(28)	2
OCI, before reclassifications to earnings and income taxes		0
Income taxes		0
OCI before reclassifications to earnings, net of income taxes		0
Amounts reclassified from AOCI to earnings, before income taxes	0	0
Income taxes	0	0
Amounts reclassified from AOCI to earnings, net of income taxes	0	0
Current-period OCI, net of income taxes	0	0
End of period	(28)	2
Derivatives designated as cash flow hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning of period	(1)	8
OCI, before reclassifications to earnings and income taxes		1
Income taxes		0
OCI before reclassifications to earnings, net of income taxes		1
Amounts reclassified from AOCI to earnings, before income taxes	(1)	(4)
Income taxes	0	1
Amounts reclassified from AOCI to earnings, net of income taxes	(1)	(3)
Current-period OCI, net of income taxes	(1)	(2)
End of period	$ (2)	$ 6

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