Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	9 Months Ended
	Dec. 31, 2019	Mar. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 6,426	$ 6,664
Accumulated Amortization	(3,062)	(2,975)
Net Carrying Amount	$ 3,364	3,689
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	11 years
Gross Carrying Amount	$ 3,602	3,818
Accumulated Amortization	(1,792)	(1,801)
Net Carrying Amount	$ 1,810	2,017
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	10 years
Gross Carrying Amount	$ 1,023	1,017
Accumulated Amortization	(479)	(430)
Net Carrying Amount	$ 544	587
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	26 years
Gross Carrying Amount	$ 517	513
Accumulated Amortization	(229)	(209)
Net Carrying Amount	$ 288	304
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	13 years
Gross Carrying Amount	$ 833	887
Accumulated Amortization	(235)	(232)
Net Carrying Amount	$ 598	655
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	4 years
Gross Carrying Amount	$ 173	141
Accumulated Amortization	(108)	(94)
Net Carrying Amount	$ 65	47
Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	5 years
Gross Carrying Amount	$ 278	288
Accumulated Amortization	(219)	(209)
Net Carrying Amount	$ 59	$ 79