Income Taxes (Effective Income Tax Rate) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate			35.00%
Income tax benefit at the federal statutory rate			$ 94	$ 202
State income taxes, net of federal income tax effect			5	16
Cumulative effect of changes in corporate state income tax laws that were recognized within State income taxes, net of federal income tax effect			3	25
Tax benefit from organizational restructuring			42	0
Change in federal and state valuation allowance			(314)	(275)
Other, net			(5)	3
Income tax benefit (expense)	$ (119)	$ (46)	$ (175)	$ (29)
Effective income tax rate			65.10%	5.00%