Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	6 Months Ended
	Sep. 30, 2019	Mar. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 6,641	$ 6,664
Accumulated Amortization	(3,152)	(2,975)
Net Carrying Amount	$ 3,489	3,689
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	11 years
Gross Carrying Amount	$ 3,787	3,818
Accumulated Amortization	(1,913)	(1,801)
Net Carrying Amount	$ 1,874	2,017
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	11 years
Gross Carrying Amount	$ 1,019	1,017
Accumulated Amortization	(461)	(430)
Net Carrying Amount	$ 558	587
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	25 years
Gross Carrying Amount	$ 530	513
Accumulated Amortization	(208)	(209)
Net Carrying Amount	$ 322	304
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	13 years
Gross Carrying Amount	$ 852	887
Accumulated Amortization	(251)	(232)
Net Carrying Amount	$ 601	655
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	4 years
Gross Carrying Amount	$ 178	141
Accumulated Amortization	(108)	(94)
Net Carrying Amount	$ 70	47
Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	5 years
Gross Carrying Amount	$ 275	288
Accumulated Amortization	(211)	(209)
Net Carrying Amount	$ 64	$ 79