Stockholders' Equity (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended								3 Months Ended	12 Months Ended	1 Months Ended					3 Months Ended	5 Months Ended	1 Months Ended		2 Months Ended	12 Months Ended	1 Months Ended
	Mar. 31, 2013	Mar. 31, 2013		Mar. 31, 2012		Mar. 31, 2011		Mar. 31, 2010		Mar. 31, 2013 Retained Earnings [Member]	Mar. 31, 2013 Retained Earnings [Member]	May 31, 2010 ASR May 2010 [Member]	Mar. 31, 2011 ASR March 2011 [Member]	May 31, 2011 ASR May 2011 [Member]	Jul. 31, 2012 ASR March 2012 [Member]	Mar. 31, 2012 ASR March 2012 [Member]	Jun. 30, 2012 ASR March 2012 [Member]	Jul. 31, 2012 ASR March 2012 [Member]	Apr. 30, 2013 ASR March 2013 [Member]	Mar. 31, 2013 ASR March 2013 [Member]	Apr. 30, 2013 ASR March 2013 [Member]	Mar. 31, 2013 Open Market Repurchases 2013 [Member]	Apr. 30, 2011 Old Rate Per Share [Member]	Apr. 30, 2011 New Rate Per Share [Member]
Stockholders' Equity [Line Items]
Quarterly dividends rate per share																							$ 0.18	$ 0.20
Cash dividends declared per common share		$ 0.80		$ 0.80		$ 0.72
Payments for repurchase of common stock		$ 1,214		$ 1,874		$ 2,050						$ 1,000	$ 275	$ 650		$ 1,200				$ 150		$ 1,000
Shares received under repurchase programs		13.0		20.0		29.0									0.6	12.0	0.9	13.5	0.2	1.2	1.4	9.9
Average price paid per share																		$ 89.10			$ 107.63	$ 101.70
Stock Repurchase Program, Remaining Authorized Repurchase Amount		340	[1]	299	[1]	499	[1]	531	[1]
Treasury Stock, Shares, Retired	1.8
Treasury Stock, Retired, Cost Method, Amount	$ 217	$ 0								$ 195	$ 195

[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.