Goodwill And Intangible Assets, Net (Information Regarding Intangible Assets) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Sep. 30, 2012	Mar. 31, 2012
Intangible assets
Gross Carrying Amount	$ 2,660	$ 2,615
Accumulated Amortization	(961)	(865)
Finite-Lived Intangible Assets, Net	1,699	1,750
Customer Lists [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	P6Y
Gross Carrying Amount	1,133	1,081
Accumulated Amortization	(607)	(554)
Finite-Lived Intangible Assets, Net	526	527
Service Agreements [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	P18Y
Gross Carrying Amount	1,003	1,022
Accumulated Amortization	(80)	(52)
Finite-Lived Intangible Assets, Net	923	970
Trademarks And Trade Names [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	P18Y
Gross Carrying Amount	199	192
Accumulated Amortization	(42)	(38)
Finite-Lived Intangible Assets, Net	157	154
Technology [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	P4Y
Gross Carrying Amount	248	244
Accumulated Amortization	(197)	(190)
Finite-Lived Intangible Assets, Net	51	54
Other [Member]
Intangible assets
Weighted Average Remaining Amortization Period (years)	P8Y
Gross Carrying Amount	77	76
Accumulated Amortization	(35)	(31)
Finite-Lived Intangible Assets, Net	$ 42	$ 45