Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Computations of basic and diluted earnings per share for Income from Continuing Operations
Net income	$ 16.7	$ 33.8	$ 45.0	$ (7.2)	$ 27.7	$ 41.8	$ 48.3	$ (1.6)	$ 88.3	$ 116.2	$ 51.1
Add: Loss from discontinued operations									0	0.9	10.7
Income from continuing operations									$ 88.3	$ 117.1	$ 61.8
Weighted-average shares outstanding - basic									52.5	54.6	55.6
Effect of dilutive securities									0.9	1.2	1.0
Weighted-average shares outstanding - diluted									53.4	55.8	56.6
Earnings per share from continuing operations:
Basic									$ 1.68	$ 2.14	$ 1.11
Diluted									$ 1.65	$ 2.10	$ 1.09