Income Taxes (Provision For (Benefit From) Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Income Tax Disclosure [Abstract]
Federal, Current	$ 138	$ 86	$ 69
State, Current	4	3	5
Foreign, Current	61	51	36
Total, Current	203	140	110
Federal, Deferred	197	96	(376)
State, Deferred	9	9	(14)
Foreign, Deferred	(3)	(2)	1
Total, Deferred	203	103	(389)
Total, Federal	335	182	(307)
Total, State	13	12	(9)
Total, Foreign	58	49	37
Total provision for (benefit from) income taxes	$ 406	$ 243	$ (279)