Segment, Major Customer and Major Supplier Information - Reconciliation from Segment Income to Consolidated Net Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting [Abstract]
Net income attributable to our common shareholder	$ 121	$ 12	$ 434	$ 502
Net loss attributable to noncontrolling interests	0	0	0	(1)
Income tax provision (benefit)	54	(6)	159	146
Loss from discontinued operations, net of tax	0	0	0	2
Income from continuing operations before income tax provision	175	6	593	649
Depreciation and amortization	139	133	406	405
Interest expense and amortization of debt issuance costs	73	75	228	198
Adjustment to reconcile proportional consolidation	8	13	33	40
Unrealized (gains) losses on change in fair value of derivative instruments, net	(15)	1	4	(20)
Realized gains on derivative instruments not included in Adjusted EBITDA	0	(1)	(4)	(3)
Loss on extinguishment of debt, net	0	0	5	0
Restructuring and impairment expenses, net	26	5	33	7
Loss on sale or disposal of assets, net	4	0	4	1
Metal price lag	45	109	62	130
Other, net	(1)	0	(5)	1
Adjusted EBITDA	$ 454	$ 341	$ 1,359	$ 1,408