Income Taxes (Schedule of Income Tax (Expense) Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Current income tax (expense) benefit
Federal	$ 0	$ 22	$ 50
State	(45)	(58)	(50)
Total current income tax (expense) benefit	(45)	(36)	0
Deferred income tax (expense) benefit
Federal	(33)	7,234	(284)
State	118	(115)	(149)
Total deferred income tax (expense) benefit	85	7,119	(433)
Foreign income tax expense	(5)	(9)	(2)
Total income tax (expense) benefit	$ 35	$ 7,074	$ (435)