Debt Obligations (2.50% Convertible Senior Notes) (Narrative) (Details) (USD $)	0 Months Ended	3 Months Ended				9 Months Ended		12 Months Ended
	Oct. 19, 2011	Dec. 31, 2011	Sep. 30, 2011	Sep. 30, 2010	Mar. 31, 2008	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Dec. 31, 2009	Feb. 28, 2010	Dec. 31, 2008
Debt Instrument [Line Items]
Charges related to debt refinancing						$ 6,000,000	$ 37,000,000
Percentage of principal amount of notes purchased if fundamental change is applied, maximum						100.00%
2.50% Convertible Senior Notes Due August 15, 2013 [Member]
Debt Instrument [Line Items]
Conversion of stock issued, conversion rate					18.1386
Convertible notes, principal amount						1,000
Convertible notes, conversion price per share of common stock						$ 55.13
Debt instrument, interest rate, stated percentage			2.50%		2.50%	2.50%				2.50%
Debt instrument convertible, number of equity instruments						7,757,283		7,757,283
Debt instrument, maturity date						Aug. 15, 2013
Debt instrument, unamortized discount			29,000,000			29,000,000		40,000,000
Debt instrument, convertible, effective interest rate			6.53%	6.53%		6.53%	6.53%
Contractual interest rate							2.50%
Debt instrument, convertible, if-converted value in excess of principal						80,000,000
Deferred income tax liabilities			32,000,000			32,000,000		32,000,000
U.S. marginal tax rate						39.55%
Capitalized debt issuance costs											10,000,000
Amortization of financing costs and discounts						1,000,000	1,000,000
Debt instrument, principal outstanding	335,000,000		428,000,000		475,000,000	428,000,000		428,000,000
Extinguishment of debt, amount									47,000,000
Convertible notes, tender offer price						1,025
Convertible notes, principal amount tendered						1,000
Tender offer expiration date						October 19, 2011
Convertible notes tender price	346,000,000
Percentage of principal amount of debt instrument holder eligible for tender offer		78.30%
Charges related to debt refinancing		$ 25,000,000