Subsequent Events (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended			213 Months Ended		0 Months Ended		12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Jan. 18, 2012 2012 Credit Facility Amendment [Member]	Feb. 20, 2014 Dividend Declared [Member]	Feb. 05, 2014 Amendment Of Revolving Credit Facility [Member]	Dec. 31, 2013 Repurchase Of Equity [Member]
Subsequent Event [Line Items]
Shares repurchased									2.7	8.1	7.9	110.3				0.6
Stock repurchased during period, value									$ 82.0	$ 190.0	$ 250.0	$ 4,680.0				$ 21.0
Number of shares held in treasury	33.8				31.1				33.8	31.1		33.8				34.4
Current Multicurrency Revolving Credit Facilty	350.0								350.0			350.0	350.0		500.0
Length of credit facility (years)													5 years
Maximum size of credit facility													$ 500.0		$ 650.0
Dividend declaration date	Oct. 24, 2013	Jul. 25, 2013	Apr. 25, 2013	Feb. 21, 2013										Feb. 20, 2014
Quarterly dividend per share of Class A Common Stock	$ 0.3	$ 0.3	$ 0.3	$ 0.3	$ 0.3	$ 0.3	$ 0.3	$ 0.25	$ 1.2	$ 1.15	$ 0.25			$ 0.3
Dividend payable date	Dec. 13, 2013	Sep. 13, 2013	Jun. 14, 2013	Mar. 15, 2013										Mar. 14, 2014
Dividend record date	Nov. 29, 2013	Aug. 30, 2013	May 31, 2013	Mar. 04, 2013										Mar. 03, 2014