Stockholders' Equity (Shares Repurchases) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Mar. 31, 2013		Apr. 30, 2015	Jan. 31, 2013		Apr. 30, 2012		Mar. 31, 2012
Stockholders' Equity Note [Abstract]
Approximate dollar value of shares that may yet to be purchased under the programs	$ 0	[1]	$ 340	[1]	$ 340	[1]						$ 299	[1]
Stock repurchase plans approved, shares							500	500	[1]	700	[1]
Repurchase of common stock	$ (340)	[1]	$ 0		$ (1,159)	[1]
Number of shares repurchased	1.5	[1],[2],[3]	0		13.0	[1],[2],[3]
Average price paid per share	$ 226.55	[1]	$ 0.00		$ 100.82	[1]

[1] This table does not include shares tendered to satisfy the exercise price in connection with cashless exercises of employee stock options or shares tendered to satisfy tax withholding obligations in connection with employee equity awards.

[2] All of the shares purchased were part of the publicly announced programs.

[3] The number of shares purchased reflects rounding adjustments.