Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Computations of basic and diluted earnings per share for income from continuing operations
Net income (loss)	$ 44.7	$ 45.0	$ 38.6	$ 37.8
(Loss) Income from discontinued operations	(3.5)	(1.1)	(9.1)	(4.8)
Income from continuing operations	$ 48.2	$ 46.1	$ 47.7	$ 42.6
Weighted-average shares outstanding - basic	51.0	53.2	50.9	53.4
Effect of diluted securities attributable to stock-based payments	0.6	1.1	0.6	1.1
Weighted-average shares outstanding - diluted	51.6	54.3	51.5	54.5
Earnings per share from continuing operations:
Basic	$ 0.95	$ 0.87	$ 0.94	$ 0.80
Diluted	$ 0.93	$ 0.85	$ 0.93	$ 0.78