Capital Stock (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Common stock, authorized (in shares)	500,000,000	500,000,000
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001
Weighted average share outstanding [Abstract]
Basic weighted-average common shares outstanding (in shares)	60,600,000	62,066,000	62,370,000
Effect of dilutive securities: Stock awards and options (in shares)	2,425,000	2,480,000	2,177,000
Diluted weighted-average common shares outstanding (in shares)	63,025,000	64,546,000	64,547,000
Securities excluded from the calculation of diluted earnings per share	100,000	0	400,000
Equity, Class of Treasury Stock [Line Items]
Class A common stock repurchased	4,600,000	1,900,000	2,200,000
Aggregate price of repurchased stock	$ 201.5	$ 67.1	$ 58.5
Increment authorized by the Company's board of directors under the stock repurchase program	250.0
Amount available for repurchases	$ 135.3
Preferred Stock [Member]
Preferred stock, authorized (in shares)	25,000,000
Preferred stock, par value (in dollars per share)	$ 0.001
Common Class A [Member]
Common stock, authorized (in shares)			500,000,000
Number of votes class is entitled to	1
Common Class B [Member]
Number of votes class is entitled to	10