Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2019	Jun. 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	$ (22)	$ 47
Effective Income Tax Rate Reconciliation, Percent	16.00%	21.00%
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	$ 14	$ (6)
Cumulative effect of changes in corporate state income tax laws that were recognized within State income taxes, net of federal income tax effect	0	(24)
Tax benefit from organizational restructuring	0	(13)
Unrecognized tax benefit	244		$ 242
Income Taxes Paid, Net	$ 27	$ 39