Treasury Stock (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Treasury Stock Disclosure [Abstract]
Stock repurchase program, authorized amount	$ 3,000,000,000
Available to repurchase common stock	86,600,000
Amount expended on share repurchases in open market transactions	100,000,000	100,000,000
Number of shares repurchased	1,378,600	1,452,100
Average per share price on share repurchases in open market transactions	$ 72.53	$ 68.83
Number of shares withheld to satisfy minimum tax withholding obligations	183,050	124,595
Total value of withheld stock	$ 14,100,000	$ 8,800,000