Debt (Narrative) (Details) (USD $)	1 Months Ended	9 Months Ended			3 Months Ended			3 Months Ended				1 Months Ended					1 Months Ended		9 Months Ended		1 Months Ended
	Feb. 28, 2011 interest_rate_swap	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2012 interest_rate_swap	Sep. 30, 2013 Senior Debt Obligations Due 2018 [Member]	Sep. 30, 2013 Senior Debt Obligations Due 2023 [Member]	Feb. 28, 2013 Senior Debt Obligations Due 2013 [Member]	Mar. 31, 2012 Senior Debt Obligations Due 2012 [Member]	Mar. 31, 2012 Senior Debt Obligations Due 2017 [Member]	Sep. 30, 2013 Senior Debt Obligations Due 2017 [Member]	Sep. 30, 2013 Revolving Credit Facility [Member]	Dec. 31, 2012 Three-Year Delayed Draw Term Loan Facility [Member]	Sep. 30, 2013 Three-Year Delayed Draw Term Loan Facility [Member]	Sep. 30, 2013 Senior Debt Obligations Due 2014 [Member]	Feb. 28, 2011 Senior Debt Obligations Due 2014 [Member]	Sep. 30, 2013 Senior Debt Obligations Due 2015 [Member]	Feb. 28, 2013 Senior Debt Obligations Due 2013 [Member]	Feb. 28, 2011 London Interbank Offered Rate (LIBOR) [Member]	Sep. 30, 2013 Interest Rate Swap [Member]	Sep. 30, 2012 Interest Rate Swap [Member]	Oct. 31, 2013 Subsequent Event [Member] Senior Debt Obligations Due 2015 [Member]
Debt Instrument [Line Items]
Proceeds from issuance of debt					$ 250,000,000	$ 250,000,000			$ 250,000,000
Interest rate					2.55%	4.05%	4.85%	6.25%	2.30%	2.30%				5.375%	5.375%	5.75%	4.85%
Repayments of Long-term Debt		257,000,000	257,000,000																		275,000,000
Gains (Losses) on Extinguishment of Debt																					24,000,000
Repaid senior notes that matured								250,000,000									250,000,000
Term of debt					5 years	10 years			5 years			3 years
Debt Instrument, Repurchase Amount																250,000,000
Line of credit facility, current borrowing capacity											1,000,000,000.0
Revolving credit facility, amount outstanding											0		50,000,000
Three-year draw term loan facility												50,000,000
Interest rate on three-year draw term loan facility													1.43%
Number of interest rate swaps	2			2
Interest rate swap for hedging	125,000,000
Interest rate swap maturity, in years	3 years 6 months
5.375% senior notes due in 2014, hedged value														250,000,000	250,000,000
Fixed interest rate of swaps															5.375%
Floating rate three-month LIBOR plus fixed spread interest percentage																		3.726%
Term of interest rate swap net settlement (in months)		6 months
Interest rate swaps, fair value adjustment	0
Swap agreements, effectiveness recognized during the period																			$ 0	$ 0