Income Taxes - Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Current:
Federal	$ 730	$ 3	$ (50)
State	257	16	42
Foreign	216	167	218
Total Current	1,203	186	210
Deferred:
Federal	(221)	(125)	95
State	(51)	17	23
Foreign	(131)	52	(40)
Total Deferred	(403)	(56)	78
Total income tax expense	$ 800	$ 130	$ 288