Earnings (Loss) Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Computations of basic and diluted earnings per share for income from continuing operations
Net income	$ 64.3	$ 44.7	$ 72.3	$ 38.6
Add: Loss from discontinued operations	0	4.8	7.8	20.2
Income from continuing operations	$ 64.3	$ 49.5	$ 80.1	$ 58.8
Weighted-average shares outstanding - basic	50.2	51.0	50.2	50.9
Effect of diluted securities attributable to stock-based payments	0.7	0.6	0.8	0.6
Weighted-average shares outstanding - diluted	50.9	51.6	51.0	51.5
Earnings per share:
Income from continuing operations, Basic	$ 1.28	$ 0.97	$ 1.60	$ 1.15
Loss from discontinued operations, Basic	$ 0.00	$ (0.09)	$ (0.16)	$ (0.39)
Net income (loss), Basic	$ 1.28	$ 0.88	$ 1.44	$ 0.76
Income from continuing operations, Diluted	$ 1.26	$ 0.96	$ 1.57	$ 1.14
Loss from discontinued operations, Diluted	$ 0.00	$ (0.09)	$ (0.15)	$ (0.39)
Net income (loss), Diluted	$ 1.26	$ 0.87	$ 1.42	$ 0.75