Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 5,758	$ 5,140
Accumulated Amortization	(2,093)	(2,119)
Net Carrying Amount	$ 3,665	3,021
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	11 years
Gross Carrying Amount	$ 2,893	2,652
Accumulated Amortization	(1,295)	(1,324)
Net Carrying Amount	$ 1,598	1,328
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	13 years
Gross Carrying Amount	$ 1,009	959
Accumulated Amortization	(316)	(269)
Net Carrying Amount	$ 693	690
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	25 years
Gross Carrying Amount	$ 741	857
Accumulated Amortization	(150)	(121)
Net Carrying Amount	$ 591	736
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	15 years
Gross Carrying Amount	$ 845	314
Accumulated Amortization	(124)	(96)
Net Carrying Amount	$ 721	218
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	4 years
Gross Carrying Amount	$ 69	195
Accumulated Amortization	(64)	(182)
Net Carrying Amount	$ 5	13
Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	5 years
Gross Carrying Amount	$ 201	163
Accumulated Amortization	(144)	(127)
Net Carrying Amount	$ 57	$ 36