Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Net income	$ 80.3	$ 67.4	$ 175.3	$ 161.2
Add: Loss from discontinued operations	0.0	0.1	0.5	0.8
Income from continuing operations	$ 80.3	$ 67.5	$ 175.8	$ 162.0
Weighted-average shares outstanding - basic	45.0	48.3	44.9	48.7
Effect of diluted securities attributable to stock-based payments	0.6	0.7	0.7	0.8
Weighted-average shares outstanding - diluted	45.6	49.0	45.6	49.5
Earnings per share:
Income from continuing operations, Basic (in dollars per share)	$ 1.78	$ 1.40	$ 3.92	$ 3.33
Loss from discontinued operations, Basic (in dollars per share)	0.00	0.00	(0.01)	(0.02)
Net income (in dollars per share)	1.78	1.40	3.91	3.31
Income from continuing operations, Diluted (in dollars per share)	1.76	1.38	3.86	3.27
Loss from discontinued operations, Diluted (in dollars per share)	0.00	0.00	(0.01)	(0.01)
Net income (in dollars per share)	$ 1.76	$ 1.38	$ 3.85	$ 3.26