Capital Stock (Narrative) (Details) (USD $)	3 Months Ended		12 Months Ended						3 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Open Market Purchases [Member]	Dec. 31, 2010 Open Market Purchases [Member]	Dec. 31, 2009 Open Market Purchases [Member]	Sep. 30, 2010 Structured Repurchase Agreements [Member]	Dec. 31, 2011 Structured Repurchase Agreements [Member]	Dec. 31, 2009 Structured Repurchase Agreements [Member]
Stock repurchase program, authorized amount			$ 3,000,000,000
Available to repurchase common stock	186,600,000		186,600,000
Amount expended on share repurchases in open market transactions			424,849,000	433,739,000	214,944,000	424,800,000	434,800,000	214,900,000
Number of shares repurchased						6,275,470	8,157,400	6,475,830
Average per share price on share repurchases in open market transactions						$ 67.70	$ 53.31	$ 33.19
Up-front payment for structured treasury stock repurchase agreement									15,000,000	0	0
Cash and premiums received under stock repurchase agreement		16,100,000
Number of shares withheld to satisfy minimum tax withholding obligations			182,203	123,489	46,732
Total value of withheld stock	$ 13,300,000	$ 6,300,000	$ 1,800,000
Preferred stock, shares authorized	5,000,000	5,000,000	5,000,000	5,000,000
Preferred stock, par value	$ 0.01	$ 0.01	$ 0.01	$ 0.01
Preferred stock, shares issued	0	0	0	0
Preferred stock, shares outstanding	0	0	0	0