Stockholders' Equity (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended				12 Months Ended	3 Months Ended	12 Months Ended		29 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Oct. 31, 2013	Dec. 31, 2011 $345million Convertible Notes March 2011 Exchange [Member]	Mar. 31, 2011 Accelerated Stock Buyback Program [Member]	Dec. 31, 2010 Accelerated Stock Buyback Program [Member]	Dec. 31, 2013 Share Repurchase Plan [Member]	Dec. 31, 2013 Share Repurchase Plan [Member]
Accelerated Share Repurchases, Settlement (Payment) or Receipt				$ 350.0
Accelerated Share Repurchases, Shares Repurchased				9.4
Accelerated Share Repurchases, Initial Price Paid Per Share	$ 29.69
Accelerated Share Repurchases, Final Price Paid	350.0
Stock Repurchase Program, Authorized Amount								300.0
Stock Repurchase Program, Period in Force								3 years
Stock Repurchased and Retired During Period, Shares						2.0		4.7	12.9
Stock Repurchased and Retired During Period, Value	(119.5)	(91.5)	(46.1)					119.5	257.1
Carrying Value of Convertible Notes Exchanged					20.3
Repurchase of shares of common stock, value	470.0	91.5	46.1				500.0
Convertible Debt Exchange Cash Paid					3.1
Extinguishment of equity component of convertible notes			25.8		25.8
Shares Issued For Exchange Of Convertible Notes, Number of Shares					2.3
Shares value issued for exchange of convertible notes					$ 44.7