Debt (Narrative) (Details) (USD $)	1 Months Ended		3 Months Ended	12 Months Ended	1 Months Ended		3 Months Ended	12 Months Ended	1 Months Ended	3 Months Ended	12 Months Ended	9 Months Ended		9 Months Ended
	May 31, 2011 Term B Loan Facility [Member]	Nov. 30, 2012 Term C Loan Facility [Member]	Mar. 31, 2013 Term C Loan Facility [Member]	Dec. 31, 2012 Term C Loan Facility [Member]	Nov. 30, 2012 Senior Unsecured Notes Due 2022 [Member]	May 31, 2011 Senior Unsecured Notes Due 2021 [Member]	Mar. 31, 2013 Senior Unsecured Notes Due 2021 [Member]	Dec. 31, 2012 Senior Unsecured Notes Due 2021 [Member]	Sep. 30, 2010 Senior Unsecured Notes Due 2018 [Member]	Mar. 31, 2013 Senior Unsecured Notes Due 2018 [Member]	Dec. 31, 2012 Senior Unsecured Notes Due 2018 [Member]	Sep. 30, 2010 Revolving Credit Facility [Member]	Mar. 31, 2013 Revolving Credit Facility [Member]	Sep. 30, 2010 Credit-Linked Revolving Facility [Member]	Mar. 31, 2013 Credit-Linked Revolving Facility [Member]	Dec. 31, 2012 Credit-Linked Revolving Facility [Member]	Mar. 31, 2013 Amended Credit Agreement [Member]
Debt Instrument [Line Items]
Senior notes					$ 500,000,000	$ 400,000,000			$ 600,000,000
Interest rate, stated percentage					4.625%	5.875%	5.875%	5.875%	6.625%	6.625%	6.625%
Line of credit facility, prepayment		400,000,000
Year of maturity	Apr. 02, 2014		Oct. 31, 2016	Oct. 31, 2016	Nov. 15, 2022	Jun. 15, 2021	Jun. 15, 2021	Jun. 15, 2021	Oct. 15, 2018	Oct. 15, 2018	Oct. 15, 2018
Notes redemption price					100.00%	100.00%			100.00%
Senior credit facilities	516,000,000		967,000,000	977,000,000									0		100,000,000	50,000,000
Revolving credit facility borrowing capacity												600,000,000	600,000,000	228,000,000
Credit facility, expiration date												Oct. 31, 2015		Apr. 02, 2014
Cross default covenant to other debt																	$ 40,000,000