Goodwill And Intangible Assets, Net (Information Regarding Intangible Assets) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Dec. 31, 2012	Mar. 31, 2012
Intangible assets
Gross Carrying Amount	$ 2,814	$ 2,615
Accumulated Amortization	(1,015)	(865)
Net Carrying Amount	1,799	1,750
Customer Lists [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	P7Y
Gross Carrying Amount	1,250	1,081
Accumulated Amortization	(637)	(554)
Net Carrying Amount	613	527
Service Agreements [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	P18Y
Gross Carrying Amount	1,022	1,022
Accumulated Amortization	(98)	(52)
Net Carrying Amount	924	970
Trademarks And Trade Names [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	P18Y
Gross Carrying Amount	199	192
Accumulated Amortization	(43)	(38)
Net Carrying Amount	156	154
Technology [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	P4Y
Gross Carrying Amount	265	244
Accumulated Amortization	(202)	(190)
Net Carrying Amount	63	54
Other [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	P7Y
Gross Carrying Amount	78	76
Accumulated Amortization	(35)	(31)
Net Carrying Amount	$ 43	$ 45