Net Income per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Basic net income per common share:
Net income	$ 42.4	$ 72.2
Weighted average common shares outstanding - Basic (in shares)	83.7	85.0
Basic net income per common share	$ 0.51	$ 0.85
Diluted net income per common share:
Net income	$ 42.4	$ 72.2
Weighted average common shares outstanding - Basic (in shares)	83.7	85.0
Plus incremental shares from assumed conversions:
Weighted average common shares outstanding - Dilutive (in shares)	84.3	86.0
Diluted net income per common share	$ 0.50	$ 0.84
Restricted Stock Units
Plus incremental shares from assumed conversions:
Incremental shares from assumed conversions	0.3	0.4
Stock Options
Plus incremental shares from assumed conversions:
Incremental shares from assumed conversions	0.3	0.6