Debt (Narrative) (Details) (USD $)	1 Months Ended	3 Months Ended			3 Months Ended			0 Months Ended		0 Months Ended		1 Months Ended				1 Months Ended		1 Months Ended		3 Months Ended
	Feb. 28, 2011 interest_rate_swap	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2011 interest_rate_swap	Mar. 31, 2014 Senior Debt Obligations Due 2018 [Member]	Mar. 31, 2014 Senior Debt Obligations Due 2023 [Member]	Mar. 31, 2014 Senior Debt Obligations Due 2017 [Member]	Mar. 28, 2014 Revolving Credit Facility [Member]	Mar. 31, 2014 Revolving Credit Facility [Member]	Mar. 28, 2014 Amended Revolving Credit Facility March 28, 2014 [Member]	Mar. 31, 2014 Amended Revolving Credit Facility March 28, 2014 [Member]	Dec. 31, 2012 Three-Year Delayed Draw Term Loan Facility [Member]	Mar. 31, 2014 Three-Year Delayed Draw Term Loan Facility [Member]	Mar. 31, 2014 Senior Debt Obligations Due 2014 [Member]	Feb. 28, 2011 Senior Debt Obligations Due 2014 [Member]	Oct. 31, 2013 Senior Debt Obligations Due 2015 [Member]	Mar. 31, 2014 Senior Debt Obligations Due 2015 [Member]	Feb. 28, 2013 Senior Debt Obligations Due 2013 [Member]	Feb. 28, 2011 London Interbank Offered Rate (LIBOR) [Member]	Mar. 31, 2014 Interest Rate Swap [Member]	Mar. 31, 2013 Interest Rate Swap [Member]	Mar. 31, 2014 Commercial Paper [Member]
Debt Instrument [Line Items]
Proceeds from issuance of debt					$ 250,000,000	$ 250,000,000
Interest rate					2.55%	4.05%	2.30%							5.375%	5.375%		5.75%	4.85%
Debt partial redemption amount																	250,000,000
Cash outflow on redemption of debt		3,000,000	252,000,000													275,000,000
Cost for early redemption																24,000,000
Repaid senior notes that matured																		250,000,000
Commercial paper		100,000,000
Commercial paper, weighted average interest rate																						0.32%
Term of debt					5 years	10 years		5 years		5 years		3 years
Line of credit facility, current borrowing capacity									1,000,000,000
Revolving credit facility, amount outstanding											0		50,000,000
Debt facilities, maximum borrowing capacity										1,200,000,000		50,000,000
Interest rate on three-year draw term loan facility													1.28%
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