Consolidated Statements of Shareholders' Equity (USD $) In Millions, except Share data, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]
BALANCE, Amount at Dec. 31, 2010	$ 2,078.9	$ 1.6	$ 2.0	$ 2,365.2	$ (289.9)
BALANCE, Shares at Dec. 31, 2010		163,562,149
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	281.4			281.4
Repurchases of common stock	(584.9)				(584.9)
Stock-based compensation expense	18.4		18.4
Shares awarded under stock-based compensation plans, including excess income tax benefit of $10.0 in 2013, $10.6 in 2012, and $22.8 in 2011	100.8		(0.8)		101.6
BALANCE, Amount at Dec. 31, 2011	1,894.6	1.6	19.6	2,646.6	(773.2)
BALANCE, Shares at Dec. 31, 2011		163,562,149
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	316.4			316.4
Repurchases of common stock	(582.3)				(582.3)
Stock-based compensation expense	18.6		18.6
Shares awarded under stock-based compensation plans, including excess income tax benefit of $10.0 in 2013, $10.6 in 2012, and $22.8 in 2011	41.2		(11.6)		52.8
BALANCE, Amount at Dec. 31, 2012	1,688.5	1.6	26.6	2,963.0	(1,302.7)
BALANCE, Shares at Dec. 31, 2012		163,562,149
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	374.9			374.9
Repurchases of common stock	(55.7)				(55.7)
Stock-based compensation expense	21.3		21.3
Shares awarded under stock-based compensation plans, including excess income tax benefit of $10.0 in 2013, $10.6 in 2012, and $22.8 in 2011	32.7		(5.1)		37.8
BALANCE, Amount at Dec. 31, 2013	$ 2,061.7	$ 1.6	$ 42.8	$ 3,337.9	$ (1,320.6)
BALANCE, Shares at Dec. 31, 2013		163,562,149