Goodwill And Intangible Assets, Net (Information Regarding Intangible Assets) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Sep. 30, 2014	Mar. 31, 2014
Intangible assets
Gross Carrying Amount	$ 5,679	$ 6,353
Accumulated Amortization	(1,580)	(1,331)
Net Carrying Amount	4,099	5,022
Customer lists
Intangible assets
Weighted Average Remaining Amortization Period (years)	9 years
Gross Carrying Amount	2,929	3,384
Accumulated Amortization	(1,003)	(863)
Net Carrying Amount	1,926	2,521
Service agreements
Intangible assets
Weighted Average Remaining Amortization Period (years)	16 years
Gross Carrying Amount	1,009	995
Accumulated Amortization	(202)	(173)
Net Carrying Amount	807	822
Pharmacy Licenses
Intangible assets
Weighted Average Remaining Amortization Period (years)	26 years
Gross Carrying Amount	995	1,219
Accumulated Amortization	(43)	(11)
Net Carrying Amount	952	1,208
Trademarks and trade names
Intangible assets
Weighted Average Remaining Amortization Period (years)	15 years
Gross Carrying Amount	360	371
Accumulated Amortization	(73)	(59)
Net Carrying Amount	287	312
Technology-Based Intangible Assets
Intangible assets
Weighted Average Remaining Amortization Period (years)	3 years
Gross Carrying Amount	217	219
Accumulated Amortization	(178)	(173)
Net Carrying Amount	39	46
Other
Intangible assets
Weighted Average Remaining Amortization Period (years)	4 years
Gross Carrying Amount	169	165
Accumulated Amortization	(81)	(52)
Net Carrying Amount	$ 88	$ 113