Earnings Per Share (Details) (USD $) In Millions, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Computations of basic and diluted earnings per share for Income from Continuing Operations
Net income	$ 33.8	$ 41.8	$ 71.6	$ 88.5
Loss from discontinued operations		0.1		0.8
Income from continuing operations	$ 33.8	$ 41.9	$ 71.6	$ 89.3
Weighted-average shares outstanding - basic	52.2	53.8	53.0	55.0
Effect of diluted securities attributable to stock-based payments	0.6	1.2	0.9	1.2
Weighted-average shares outstanding - diluted	52.8	55.0	53.9	56.2
Earnings per share from continuing operations:
Basic	$ 0.65	$ 0.78	$ 1.35	$ 1.62
Diluted	$ 0.64	$ 0.76	$ 1.33	$ 1.59