Stockholders' Equity (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	1 Months Ended		3 Months Ended		9 Months Ended			1 Months Ended	2 Months Ended		4 Months Ended	1 Months Ended		3 Months Ended	1 Months Ended
	Jan. 31, 2012	Apr. 30, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Mar. 31, 2011	May 31, 2011 ASR May 2011 Program [Member]	Aug. 31, 2011 ASR May 2011 Program [Member]	Jun. 30, 2011 ASR May 2011 Program [Member]	Aug. 31, 2011 ASR May 2011 Program [Member]	May 31, 2011 ASR March 2011 Program [Member]	Mar. 31, 2011 ASR March 2011 Program [Member]	May 31, 2011 ASR March 2011 Program [Member]	Apr. 30, 2011 Old Rate Per Share [Member]	Apr. 30, 2011 New Rate Per Share [Member]
Stockholders' Equity [Line Items]
Additional shares received under ASR									1.3	6.7		0.4	3.1
Authorized amount of common stock repurchase plan	$ 650	$ 1,000						$ 650					$ 275
Average price paid per share											$ 81.50			$ 79.65
Total shares received under ASR			126.0		126.0		117.0		8.0		8.0	3.5		3.5
Stockholders Equity
Dividends rate per share															$ 0.18	$ 0.20
Cash dividends declared per common share			$ 0.20	$ 0.18	$ 0.60	$ 0.54
Total repurchase authorization outstanding	$ 1,500	$ 1,500			$ 850