Goodwill And Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	9 Months Ended
	Dec. 31, 2015	Mar. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 5,162	$ 5,204
Accumulated Amortization	(2,059)	(1,763)
Net Carrying Amount	$ 3,103	3,441
Customer lists
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	8 years
Gross Carrying Amount	$ 2,663	2,683
Accumulated Amortization	(1,295)	(1,116)
Net Carrying Amount	$ 1,368	1,567
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	15 years
Gross Carrying Amount	$ 943	957
Accumulated Amortization	(251)	(215)
Net Carrying Amount	$ 692	742
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	25 years
Gross Carrying Amount	$ 884	874
Accumulated Amortization	(111)	(65)
Net Carrying Amount	$ 773	809
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	14 years
Gross Carrying Amount	$ 300	315
Accumulated Amortization	(90)	(82)
Net Carrying Amount	$ 210	233
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	2 years
Gross Carrying Amount	$ 209	213
Accumulated Amortization	(193)	(184)
Net Carrying Amount	$ 16	29
Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	3 years
Gross Carrying Amount	$ 163	162
Accumulated Amortization	(119)	(101)
Net Carrying Amount	$ 44	$ 61