Treasury Stock (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Sep. 30, 2011
Treasury Stock Disclosure [Abstract]
Stock repurchase program, authorized amount	$ 3,400,000,000
Available to repurchase common stock	274,200,000
Amount expended on share repurchases in open market transactions	61,400,000	100,000,000
Number of shares repurchased	860,500	1,378,600
Average per share price on share repurchases in open market transactions	$ 71.31	$ 72.53
Number of shares withheld to satisfy minimum tax withholding obligations	322,538		183,050
Total value of withheld stock	$ 23,200,000		$ 14,100,000