Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Computations of basic and diluted earnings per share for income from continuing operations
Net income	$ 21.9	$ 29.4	$ 44.7	$ (6.1)	$ 16.7	$ 33.8	$ 45.0	$ (7.2)	$ 90.0	$ 88.3	$ 116.2
Add: Loss from discontinued operations									45.0	23.2	9.7
Income from continuing operations									$ 135.0	$ 111.5	$ 125.9
Weighted-average shares outstanding - basic									50.7	52.5	54.6
Effect of diluted securities attributable to stock-based payments									0.7	0.9	1.2
Weighted-average shares outstanding - diluted									51.4	53.4	55.8
Earnings per share from continuing operations:
Basic									$ 2.66	$ 2.12	$ 2.31
Diluted									$ 2.63	$ 2.09	$ 2.26