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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, 2018	Mar. 31, 2017	Mar. 31, 2016
Income Tax Disclosure [Abstract]
Income tax expense at federal statutory rate	$ 75	$ 2,411	$ 1,137
State income taxes net of federal tax benefit	50	153	92
Tax effect of foreign operations	(146)	(326)	(295)
Unrecognized tax benefits and settlements	454	57	(14)
Non-deductible goodwill	585	106	0
Share-based compensation	(8)	(54)	0
Net tax benefit on intellectual property transfer	(178)	(137)	0
Rate differential on gain from Change Healthcare Net Asset Exchange	0	(587)	0
Remeasurement of U.S. deferred taxes	(1,324)	0	0
Transition tax on foreign earnings	457	0	0
Other, net	(18)	(9)	(12)
Income tax (benefit) expense	$ (53)	$ 1,614	$ 908

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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