Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	6 Months Ended
	Sep. 30, 2020	Mar. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 6,529	$ 6,392
Accumulated Amortization	(3,499)	(3,236)
Net Carrying Amount	$ 3,030	3,156
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	12 years
Gross Carrying Amount	$ 3,736	3,650
Accumulated Amortization	(2,127)	(1,950)
Net Carrying Amount	$ 1,609	1,700
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	10 years
Gross Carrying Amount	$ 997	994
Accumulated Amortization	(506)	(480)
Net Carrying Amount	$ 491	514
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	26 years
Gross Carrying Amount	$ 502	492
Accumulated Amortization	(222)	(232)
Net Carrying Amount	$ 280	260
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	12 years
Gross Carrying Amount	$ 894	808
Accumulated Amortization	(314)	(242)
Net Carrying Amount	$ 580	566
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	5 years
Gross Carrying Amount	$ 147	175
Accumulated Amortization	(113)	(111)
Net Carrying Amount	$ 34	64
Other
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	5 years
Gross Carrying Amount	$ 253	273
Accumulated Amortization	(217)	(221)
Net Carrying Amount	$ 36	$ 52