Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 6,392	$ 6,664
Accumulated Amortization	(3,236)	(2,975)
Net Carrying Amount	$ 3,156	3,689
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	11 years
Gross Carrying Amount	$ 3,650	3,818
Accumulated Amortization	(1,950)	(1,801)
Net Carrying Amount	$ 1,700	2,017
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	10 years
Gross Carrying Amount	$ 994	1,017
Accumulated Amortization	(480)	(430)
Net Carrying Amount	$ 514	587
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	26 years
Gross Carrying Amount	$ 492	513
Accumulated Amortization	(232)	(209)
Net Carrying Amount	$ 260	304
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	13 years
Gross Carrying Amount	$ 808	887
Accumulated Amortization	(242)	(232)
Net Carrying Amount	$ 566	655
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	3 years
Gross Carrying Amount	$ 175	141
Accumulated Amortization	(111)	(94)
Net Carrying Amount	$ 64	47
Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	5 years
Gross Carrying Amount	$ 273	288
Accumulated Amortization	(221)	(209)
Net Carrying Amount	$ 52	$ 79