Income Taxes (Schedule of Income Tax (Expense) Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Current income tax (expense) benefit
Federal	$ 50	$ 13	$ 5
State	(50)	(30)	(39)
Total current income tax (expense) benefit	0	(17)	(34)
Deferred income tax (expense) benefit
Federal	(284)	(206)	491
State	(149)	83	118
Total deferred income tax (expense) benefit	(433)	(123)	609
Foreign income tax expense	(2)	(1)	(1)
Total income tax (expense) benefit	$ (435)	$ (141)	$ 574