Treasury Stock (Details) (USD $)	3 Months Ended		9 Months Ended		1 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Jul. 31, 2012 Stock Repurchase Authorization [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount			$ 3,400,000,000
Stock repurchase program, additional authorized amount					400,000,000
Available to repurchase common stock			411,700,000
Amount expended on share repurchases in open market transactions	75,000,000	125,000,000	175,000,000	324,900,000
Number of shares repurchased	983,200	2,205,270	2,361,800	4,865,770
Average per share price on share repurchases in open market transactions	$ 76.24	$ 56.68	$ 74.08	$ 66.77
Number of shares withheld to satisfy minimum tax withholding obligations	31,733	1,998	227,604	165,738
Total value of withheld stock	$ 2,500,000	$ 100,000	$ 17,500,000	$ 12,200,000