Stockholders' Equity (Shares Repurchased Over Last Three Years) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012		Mar. 31, 2011
Class of Stock [Line Items]
Number of shares repurchased	0	[1],[2],[3]	13	[1],[2],[3]	20	[1],[2],[3]
Average price paid per share	$ 0.00	[2]	$ 100.82	[2]	$ 83.47	[2]
Stock Repurchase Program, Remaining Authorized Repurchase Amount, End of Period	$ 340	[2]	$ 340	[2]	$ 299	[2]	$ 499	[2]
Repurchase of common stock	0	[2]	(1,159)		(1,850)	[2]
Stock Repurchase Approved, April 2011 [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount					1,000	[2]
Stock Repurchase Approved January 2012 [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount					650	[2]
Stock Repurchase Approved April 2012 [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount			700	[2]
Stock Repurchase Approved January 2013 [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount			$ 500	[2]

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

[2] 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.

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