Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 6,646	$ 6,392
Accumulated Amortization	(3,768)	(3,236)
Net Carrying Amount	$ 2,878	3,156
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	12 years
Gross Carrying Amount	$ 3,739	3,650
Accumulated Amortization	(2,269)	(1,950)
Net Carrying Amount	$ 1,470	1,700
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	10 years
Gross Carrying Amount	$ 1,081	994
Accumulated Amortization	(513)	(480)
Net Carrying Amount	$ 568	514
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	23 years
Gross Carrying Amount	$ 497	492
Accumulated Amortization	(244)	(232)
Net Carrying Amount	$ 253	260
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	12 years
Gross Carrying Amount	$ 925	808
Accumulated Amortization	(394)	(242)
Net Carrying Amount	$ 531	566
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	4 years
Gross Carrying Amount	$ 150	175
Accumulated Amortization	(122)	(111)
Net Carrying Amount	$ 28	64
Other
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	6 years
Gross Carrying Amount	$ 254	273
Accumulated Amortization	(226)	(221)
Net Carrying Amount	$ 28	$ 52