Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 5,140	$ 5,204
Accumulated Amortization	(2,119)	(1,763)
Net Carrying Amount	$ 3,021	3,441
Customer lists
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	7 years
Gross Carrying Amount	$ 2,652	2,683
Accumulated Amortization	(1,324)	(1,116)
Net Carrying Amount	$ 1,328	1,567
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	14 years
Gross Carrying Amount	$ 959	957
Accumulated Amortization	(269)	(215)
Net Carrying Amount	$ 690	742
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	25 years
Gross Carrying Amount	$ 857	874
Accumulated Amortization	(121)	(65)
Net Carrying Amount	$ 736	809
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	14 years
Gross Carrying Amount	$ 314	315
Accumulated Amortization	(96)	(82)
Net Carrying Amount	$ 218	233
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	2 years
Gross Carrying Amount	$ 195	213
Accumulated Amortization	(182)	(184)
Net Carrying Amount	$ 13	29
Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (Years)	3 years
Gross Carrying Amount	$ 163	162
Accumulated Amortization	(127)	(101)
Net Carrying Amount	$ 36	$ 61