Income Taxes (Provision For (Benefit From) Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Federal, Current	$ 29	$ 138	$ 86
State, Current	5	4	3
Foreign, Current	42	61	51
Total, Current	76	203	140
Federal, Deferred	(18)	197	96
State, Deferred	0	9	9
Foreign, Deferred	2	(3)	(2)
Total, Deferred	(16)	203	103
Total, Federal	11	335	182
Total, State	5	13	12
Total, Foreign	44	58	49
Total provision for (benefit from) income taxes	$ 60	$ 406	$ 243