Stockholder's Equity (Shares Repurchased Over Last Three Years) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Mar. 31, 2012		Mar. 31, 2011		Mar. 31, 2010
Stockholders' Equity [Abstract]
Number of shares repurchased	20	[1]	29	[1]	8	[1]
Average price paid per share	$ 83.47		$ 69.62		$ 41.47
Total value of shares repurchased	$ 1,850		$ 2,032		$ 299

[1] Excludes shares surrendered for tax withholding.