Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%
Income tax benefit	$ (408)	$ (8)	$ (494)	$ 56
Effective Income Tax Rate Reconciliation, Percent			49.00%	19.20%
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount			$ (236)	$ (12)
Tax benefit to reduce valuation allowance			304
Cumulative effect of changes in corporate state income tax laws that were recognized within State income taxes, net of federal income tax effect			(6)	(62)
Tax benefit from organizational restructuring			4	(12)
Unrecognized tax benefit	$ 249		249		$ 242
Income Taxes Paid, Net			$ 47	$ 62