Equity (Details) (USD $)	0 Months Ended	3 Months Ended	9 Months Ended
	Aug. 24, 2010	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Treasury Stock
Authorized amount of common stock repurchase (in dollars)	$ 200,000,000
Treasury stock (in shares)		3,994,940		4,160,228
Amount of shares repurchased including transaction costs (in dollars)		154,300,000		162,077,000
Average cost of per share repurchased (in dollars per share)		$ 38.63		$ 38.96
Treasury shares cancelled and retired			5,278,828
Treasury Stock
Treasury Stock Activity
Reduction in treasury stock due to retirement			200,200,000
Retained Earnings
Treasury Stock Activity
Reduction due to retirement of treasury stock			200,100,000
Common Stock
Treasury Stock Activity
Reduction due to retirement of treasury stock			$ 100,000