Income Taxes (Effective Income Tax Rate) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2015	Jun. 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	$ 13	$ (3)
State income taxes, net of federal income tax effect	(1)	(7)
Cumulative effect of changes in corporate state income tax laws that were recognized within State income taxes, net of federal income tax effect	(21)	0
Change in federal and state valuation allowance	(22)	27
Other, net	6	(2)
Income tax benefit (expense)	$ 17	$ 15
Effective income tax rate	(45.90%)	187.50%