Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	6 Months Ended
	Sep. 30, 2021	Mar. 31, 2021
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 5,894	$ 6,646
Accumulated Amortization	(3,509)	(3,768)
Net Carrying Amount	$ 2,385	2,878
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	12 years
Gross Carrying Amount	$ 3,241	3,739
Accumulated Amortization	(2,017)	(2,269)
Net Carrying Amount	$ 1,224	1,470
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	10 years
Gross Carrying Amount	$ 1,082	1,081
Accumulated Amortization	(542)	(513)
Net Carrying Amount	$ 540	568
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	22 years
Gross Carrying Amount	$ 308	497
Accumulated Amortization	(209)	(244)
Net Carrying Amount	$ 99	253
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	12 years
Gross Carrying Amount	$ 872	925
Accumulated Amortization	(394)	(394)
Net Carrying Amount	$ 478	531
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	3 years
Gross Carrying Amount	$ 136	150
Accumulated Amortization	(116)	(122)
Net Carrying Amount	$ 20	28
Other
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	7 years
Gross Carrying Amount	$ 255	254
Accumulated Amortization	(231)	(226)
Net Carrying Amount	$ 24	$ 28