Income Taxes - Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]
Federal	$ (50)	$ 392	$ (32)
State	42	16	14
Foreign	218	247	36
Total Current	210	655	18
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Federal	95	(899)	(7)
State	23	(59)	(1)
Foreign	(40)	61	(84)
Total Deferred	78	(897)	(92)
Total income tax (benefit) expense	$ 288	$ (242)	$ (74)