Stockholders' Equity (Details) (USD $)	12 Months Ended							12 Months Ended	3 Months Ended	8 Months Ended	12 Months Ended		17 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2010 $550million Medium Term Notes [Member]	Dec. 31, 2010 $300million Medium Term Notes [Member]	Dec. 31, 2010 $345million Converitble Notes [Member]	Dec. 31, 2009 $345million Converitble Notes [Member]	Dec. 31, 2011 $345million Convertible Notes March 2011 Exchange [Member]	Mar. 31, 2011 Accelerated Stock Buyback Program [Member]	Mar. 24, 2011 Accelerated Stock Buyback Program [Member]	Dec. 31, 2010 Accelerated Stock Buyback Program [Member]	Dec. 31, 2012 Share Repurchase Plan [Member]	Dec. 31, 2012 Share Repurchase Plan [Member]
Stock Repurchase Program, Authorized Amount												$ 300,000,000
Stock Repurchase Program, Period in Force												3 years
Stock Repurchased and Retired During Period, Shares									2,000,000		25,800,000	4,900,000	8,300,000
Stock Repurchased and Retired During Period, Value	91,500,000	46,100,000										91,500,000	137,600,000
Debt Instrument, Face Amount				550,000,000	300,000,000		345,000,000
Debt Instrument, Convertible, Conversion Ratio			116.198
Convertible Debt Exchange Cash Paid Per Unit						160
Convertible Notes Face Value Subject To Exchange Min			1,000
Carrying Value of Convertible Notes Exchanged			324,700,000					20,300,000
Shares issued for exchange of convertible notes, Shares			37,700,000
Debt Instrument, Interest Rate, Stated Percentage				4.70%	10.60%
Debt Instrument, Maturity Date				Aug. 15, 2020	Apr. 15, 2019	Mar. 15, 2014
Repurchase of shares of common stock, value	91,500,000	46,100,000	500,100,000								500,000,000
Daily volume-weighted average share price										$ 17.95
Convertible Debt Exchange Cash Paid			52,000,000					3,100,000
Extinguishment of equity component of convertible notes		25,800,000	334,400,000					25,800,000
Shares Issued For Exchange Of Convertible Notes, Number of Shares								2,300,000
Shares value issued for exchange of convertible notes			638,000,000					44,700,000
Proceeds from settlement of call options	0	0	369,500,000
Payments for Repurchase of Warrants	$ 0	$ 0	$ 298,400,000