Subsequent Event (Details) (Repurchase of Equity, Common Stock, USD $) In Millions, except Per Share data, unless otherwise specified	1 Months Ended
	May 16, 2012	Jun. 01, 2012
Repurchase of Equity | Common Stock
Subsequent Event
Stock Repurchase Program, Authorized Amount	$ 500.0
Stock Repurchase Program, Remaining Authorized Repurchase Amount	623.9
Treasury Stock, Shares, Retired		8.7
Treasury Stock, Retired, Cost Method, Amount		$ 45.1
Treasury Stock Acquired, Average Cost Per Share		$ 5.18