Income Taxes (Schedule of Income Tax (Expense) Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Current income tax (expense) benefit
Federal	$ 22	$ 50	$ 13
State	(58)	(50)	(30)
Total current income tax (expense) benefit	(36)	0	(17)
Deferred income tax (expense) benefit
Federal	7,234	(284)	(206)
State	(115)	(149)	83
Total deferred income tax (expense) benefit	7,119	(433)	(123)
Foreign income tax expense	(9)	(2)	(1)
Total income tax (expense) benefit	$ 7,074	$ (435)	$ (141)