Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Earnings Per Share [Abstract]
Net income	$ 43.5	$ 24.9
Add: Loss from discontinued operations	0.0	0.0
Income from continuing operations	$ 43.5	$ 24.9
Weighted-average shares outstanding – basic	42.8	44.0
Add: Potential effect of dilutive securities attributable to stock-based payments	0.7	0.7
Weighted-average shares outstanding – diluted	43.5	44.7
Earnings per share – Basic:
Income from continuing operations (in dollars per share)	$ 1.02	$ 0.57
Loss from discontinued operations (in dollars per share)	0.00	0.00
Net income (in dollars per share)	1.02	0.57
Earnings per share – Diluted:
Income from continuing operations (in dollars per share)	1.00	0.56
Loss from discontinued operations (in dollars per share)	0.00	0.00
Net income (in dollars per share)	$ 1.00	$ 0.56