Share-Based Compensation (Stock Option Activity) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Mar. 31, 2012 Y		Mar. 31, 2011 Y		Mar. 31, 2010 Y
Share-Based Compensation [Abstract]
Shares Outstanding, Beginning balance	9		16		19
Granted, Shares	1		1		2
Exercised, Shares	(2)		(8)		(5)
Shares Outstanding, Ending balance	8		9		16
Vested and expected to vest, Shares	7	[1]
Vested and exercisable, Shares	4
Outstanding, Weighted-Average Exercise Price, Beginning of period	$ 49.01		$ 41.26		$ 39.28
Granted, Weighted-Average Exercise Price	$ 83.30		$ 67.95		$ 40.59
Exercised, Weighted-Average Exercise Price	$ 42.20		$ 37.63		$ 33.34
Outstanding, Weighted-Average Exercise Price, End of period	$ 56.88		$ 49.01		$ 41.26
Vested and expected to vest, Weighted-Average Exercise Price	$ 56.71	[1]
Vested and exercisable, Weighted-Average Exercise Price	$ 49.86
Outstanding, Weighted-Average Remaining Contractual Term, Beginning of period, years	4		3		3
Outstanding, Weighted-Average Remaining Contractual Term, End of period, years	4		4		3
Vested and expected to vest, Weighted-Average Remaining Contractual Term, years	4	[1]
Vested and exercisable, Weighted-Average Remaining Contractual Term, years	3
Outstanding, Aggregate Intrinsic Value, Beginning of period	$ 269	[2]	$ 394	[2]	$ 33	[2]
Outstanding, Aggregate Intrinsic Value, End of period	226	[2]	269	[2]	394	[2]
Vested and expected to vest, Aggregate Intrinsic Value	225	[1],[2]
Vested and exercisable, Aggregate Intrinsic Value	$ 142	[2]

[1] The number of options expected to vest takes into account an estimate of expected forfeitures.

[2] The intrinsic value is calculated as the difference between the period-end market price of the Company's common stock and the exercise price of "in-the-money" options.