Debt (Narrative) (Details) (USD $)	1 Months Ended	9 Months Ended	12 Months Ended	1 Months Ended	9 Months Ended	12 Months Ended	1 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended		9 Months Ended
	May 31, 2011 Term B Loan Facility [Member]	Sep. 30, 2012 Term C Loan Facility [Member]	Dec. 31, 2011 Term C Loan Facility [Member]	Sep. 30, 2010 Senior Unsecured Notes Due 2018 [Member]	Sep. 30, 2012 Senior Unsecured Notes Due 2018 [Member]	Dec. 31, 2011 Senior Unsecured Notes Due 2018 [Member]	May 31, 2011 Senior Unsecured Notes Due 2021 [Member]	Sep. 30, 2012 Senior Unsecured Notes Due 2021 [Member]	Dec. 31, 2011 Senior Unsecured Notes Due 2021 [Member]	Sep. 30, 2010 Revolving Credit Facility [Member]	Sep. 30, 2012 Revolving Credit Facility [Member]	Sep. 30, 2010 Credit-Linked Revolving Facility [Member]	Sep. 30, 2012 Amended Credit Agreement [Member]
Debt Instrument [Line Items]
Senior notes				$ 600,000,000			$ 400,000,000
Interest rate, stated percentage				6.625%	6.625%	6.625%	5.875%	5.875%	5.875%
Year of maturity	Apr. 02, 2014	Oct. 31, 2016	Oct. 31, 2016	Oct. 15, 2018	Oct. 15, 2018	Oct. 15, 2018	Jun. 15, 2021	Jun. 15, 2021	Jun. 15, 2021
Notes redemption price				100.00%			100.00%
Senior credit facilities	516,000,000	1,375,000,000	1,386,000,000								0
Revolving credit facility borrowing capacity										600,000,000	600,000,000	228,000,000
Revolving credit facility, expiration date										Oct. 31, 2015		Apr. 02, 2014
Cross default covenant to other debt													$ 40,000,000