Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 6,681	$ 5,758
Accumulated Amortization	(2,579)	(2,093)
Net Carrying Amount	$ 4,102	3,665
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	12 years
Gross Carrying Amount	$ 3,619	2,893
Accumulated Amortization	(1,550)	(1,295)
Net Carrying Amount	$ 2,069	1,598
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	12 years
Gross Carrying Amount	$ 1,037	1,009
Accumulated Amortization	(386)	(316)
Net Carrying Amount	$ 651	693
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	26 years
Gross Carrying Amount	$ 684	741
Accumulated Amortization	(196)	(150)
Net Carrying Amount	$ 488	591
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	14 years
Gross Carrying Amount	$ 932	845
Accumulated Amortization	(187)	(124)
Net Carrying Amount	$ 745	721
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	4 years
Gross Carrying Amount	$ 147	69
Accumulated Amortization	(84)	(64)
Net Carrying Amount	$ 63	5
Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	4 years
Gross Carrying Amount	$ 262	201
Accumulated Amortization	(176)	(144)
Net Carrying Amount	$ 86	$ 57