Income Taxes - Reconciliation Between Effective Tax Rate On Income From Continuing Operations And Statutory Tax Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Income tax expense at federal statutory rate	$ 128	$ 75	$ 2,411
State income taxes net of federal tax benefit	70	50	153
Tax effect of foreign operations	(86)	(146)	(326)
Unrecognized tax benefits and settlements	20	454	57
Non-deductible goodwill	357	585	106
Share-based compensation	4	(8)	(54)
Net tax benefit on intellectual property transfer	(42)	(178)	(137)
Rate differential on gain from Change Healthcare Net Asset Exchange	0	0	(587)
Impact of change in U.S. tax rate on temporary differences	(81)	(1,324)	0
Transition tax on foreign earnings	(5)	457	0
Other, net	(9)	(18)	(9)
Income tax expense (benefit)	$ 356	$ (53)	$ 1,614