Income Taxes (Effective Income Tax Rate) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 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			$ 460	$ 1,303
State income taxes, net of federal income tax effect			33	96
Cumulative effect of changes in corporate state income tax laws that were recognized within State income taxes, net of federal income tax effect			(23)	0
Change in federal and state valuation allowance			(647)	(797)
Other, net			5	(1)
Income tax benefit (expense)	$ (97)	$ 657	$ (126)	$ 601
Effective income tax rate			9.60%	(16.10%)