Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 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	$ (64)	$ 17	$ (86)	$ 64
Effective Income Tax Rate Reconciliation, Percent			18.00%	14.40%
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount			$ 37	$ (11)
Cumulative effect of changes in corporate state income tax laws that were recognized within State income taxes, net of federal income tax effect			1	(59)
Tax benefit from organizational restructuring			4	(13)
Unrecognized tax benefit	$ 247		247		$ 242
Income Taxes Paid, Net			$ 37	$ 53