Net Income Per Common Share - Summary of Earnings Per Share Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Basic net income per common share:
Net income	$ 9.7	$ (1.0)	$ 42.4	$ 80.3	$ 80.9	$ 72.2	$ 51.1	$ 233.4
Weighted average common shares outstanding - Basic (in shares)	83.8			85.1			83.7	85.1
Basic net income per common share	$ 0.12			$ 0.94			$ 0.61	$ 2.74
Diluted net income per common share:
Net income	$ 9.7			$ 80.3			$ 51.1	$ 233.4
Weighted average common shares outstanding - Basic (in shares)	83.8			85.1			83.7	85.1
Plus incremental shares from assumed conversions:
Weighted average common shares outstanding - Dilutive (in shares)	84.0			86.1			84.0	86.1
Diluted net income per common share	$ 0.12			$ 0.93			$ 0.61	$ 2.71
Restricted Stock Units
Plus incremental shares from assumed conversions:
Incremental shares from assumed conversions	0.1			0.4			0.2	0.4
Stock Options
Plus incremental shares from assumed conversions:
Incremental shares from assumed conversions	0.1			0.6			0.1	0.6