Earnings Per Share (Details) (USD $) In Millions, except 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
Numerator:
Numerator for basic earnings per share									$ 141.6	$ 133.6	$ 132.9
Earnings attributable to participating securities									0	0.1	0.2
Reported net income (Numerator for diluted earnings per share)									$ 141.6	$ 133.7	$ 133.1
Denominator:
Weighted average common shares outstanding (Basic earnings per share) (in shares)									81,800,000	81,200,000	80,700,000
Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock and contingent share method (in shares)									0	100,000	300,000
Adjusted weighted average shares outstanding and assumed conversions outstanding (Diluted earnings per share) (in shares)									81,800,000	81,300,000	81,000,000
Basic earnings per share (in dollars per share)	$ 0.56	$ 0.43	$ 0.19	$ 0.55	$ 0.56	$ 0.20	$ 0.11	$ 0.78	$ 1.73	$ 1.65	$ 1.65
Diluted earnings per share (in dollars per share)	$ 0.56	$ 0.43	$ 0.18	$ 0.55	$ 0.55	$ 0.20	$ 0.11	$ 0.78	$ 1.73	$ 1.64	$ 1.64
Antidilutive securities excluded from computation of diluted earnings per share (in shares)									0	308,800	837,100
Stock options, exercise prices range , lower range limit (in dollars per share)										$ 24.90	$ 23.19
Stock options, exercise prices range , upper range limit (in dollars per share)										$ 27.15	$ 27.15