Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2021	Mar. 31, 2021
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 6,677	$ 6,646
Accumulated Amortization	(3,880)	(3,768)
Net Carrying Amount	$ 2,797	2,878
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	12 years
Gross Carrying Amount	$ 3,747	3,739
Accumulated Amortization	(2,329)	(2,269)
Net Carrying Amount	$ 1,418	1,470
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	10 years
Gross Carrying Amount	$ 1,088	1,081
Accumulated Amortization	(530)	(513)
Net Carrying Amount	$ 558	568
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	23 years
Gross Carrying Amount	$ 503	497
Accumulated Amortization	(252)	(244)
Net Carrying Amount	$ 251	253
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	12 years
Gross Carrying Amount	$ 934	925
Accumulated Amortization	(412)	(394)
Net Carrying Amount	$ 522	531
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	4 years
Gross Carrying Amount	$ 150	150
Accumulated Amortization	(127)	(122)
Net Carrying Amount	$ 23	28
Other
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	6 years
Gross Carrying Amount	$ 255	254
Accumulated Amortization	(230)	(226)
Net Carrying Amount	$ 25	$ 28