Income Taxes (Effective Income Tax Rate) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
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			$ 202	$ 240
State income taxes, net of federal income tax effect			16	0
Cumulative effect of changes in corporate state income tax laws that were recognized within State income taxes, net of federal income tax effect			(25)	0
Change in federal and state valuation allowance			(275)	(297)
Other, net			3	1
Income tax benefit (expense)	$ (46)	$ (71)	$ (29)	$ (56)
Effective income tax rate			5.00%	8.20%