Net Income per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Basic net income per common share:
Net Income	$ 56.0	$ 68.1
Weighted average common shares outstanding (in shares)	93.4	96.2
Basic net income per common share ( in dollars per share)	$ 0.60	$ 0.71
Diluted net income per common share:
Net income	$ 56.0	$ 68.1
Weighted average common shares outstanding (in shares)	93.4	96.2
Plus incremental shares from assumed conversions:
Restricted stock units (in shares)	0.4	0.6
Stock options (in shares)	1.0	1.1
Weighted average common shares outstanding - Dilutive (in shares)	94.8	97.9
Diluted net income per common share (in dollars per share)	$ 0.59	$ 0.70