Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	9 Months Ended
	Dec. 31, 2020	Mar. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 6,660	$ 6,392
Accumulated Amortization	(3,680)	(3,236)
Net Carrying Amount	$ 2,980	3,156
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	12 years
Gross Carrying Amount	$ 3,972	3,650
Accumulated Amortization	(2,318)	(1,950)
Net Carrying Amount	$ 1,654	1,700
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	10 years
Gross Carrying Amount	$ 859	994
Accumulated Amortization	(402)	(480)
Net Carrying Amount	$ 457	514
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	26 years
Gross Carrying Amount	$ 503	492
Accumulated Amortization	(240)	(232)
Net Carrying Amount	$ 263	260
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	12 years
Gross Carrying Amount	$ 922	808
Accumulated Amortization	(379)	(242)
Net Carrying Amount	$ 543	566
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	5 years
Gross Carrying Amount	$ 149	175
Accumulated Amortization	(118)	(111)
Net Carrying Amount	$ 31	64
Other
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Amortization Period (Years)	5 years
Gross Carrying Amount	$ 255	273
Accumulated Amortization	(223)	(221)
Net Carrying Amount	$ 32	$ 52