Income Taxes (Effective Income Tax Rate) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2016	Jun. 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	$ 86	$ 13
State income taxes, net of federal income tax effect	3	(1)
Cumulative effect of changes in corporate state income tax laws that were recognized within State income taxes, net of federal income tax effect	0	21
Change in federal and state valuation allowance	(142)	(22)
Other, net	(3)	6
Income tax benefit (expense)	$ (56)	$ 17
Effective income tax rate	22.80%	(45.90%)