Goodwill and Intangible Assets, Net (Information Regarding Intangible Assets) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Intangible assets
Gross Carrying Amount	$ 6,353	$ 3,347
Accumulated Amortization	(1,331)	(1,077)
Net Carrying Amount	5,022	2,270
Customer Lists [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	10 years
Gross Carrying Amount	3,384	1,761
Accumulated Amortization	(863)	(672)
Net Carrying Amount	2,521	1,089
Service Agreements [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	16 years
Gross Carrying Amount	995	1,018
Accumulated Amortization	(173)	(114)
Net Carrying Amount	822	904
Pharmacy Licenses [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	26 years
Gross Carrying Amount	1,219	0
Accumulated Amortization	(11)	0
Net Carrying Amount	1,208	0
Trademarks and Trade Names [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	15 years
Gross Carrying Amount	371	208
Accumulated Amortization	(59)	(46)
Net Carrying Amount	312	162
Technology [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	3 years
Gross Carrying Amount	219	271
Accumulated Amortization	(173)	(207)
Net Carrying Amount	46	64
Other Intangible Assets [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	5 years
Gross Carrying Amount	165	89
Accumulated Amortization	(52)	(38)
Net Carrying Amount	$ 113	$ 51