Net Income (Loss) Per Common Share - Summary of Earnings Per Share Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Basic net income (loss) per common share:
Net income (loss)		$ (1.0)	$ 42.4	$ 80.9	$ 72.2	$ 41.4	$ 153.1
Weighted average common shares outstanding - Basic (in shares)		83.7		85.2		83.7	85.1
Basic net income (loss) per common share		$ (0.01)		$ 0.95		$ 0.49	$ 1.80
Diluted net income (loss) per common share:
Net income (loss)		$ (1.0)		$ 80.9		$ 41.4	$ 153.1
Weighted average common shares outstanding - Basic (in shares)		83.7		85.2		83.7	85.1
Plus incremental shares from assumed conversions:
Weighted average common shares outstanding - Dilutive (in shares)	[1]	83.7		86.2		84.1	86.1
Diluted net (loss) income per common share	[1]	$ (0.01)		$ 0.94		$ 0.49	$ 1.78
Restricted Stock Units
Plus incremental shares from assumed conversions:
Incremental shares from assumed conversions				0.4		0.2	0.4
Stock Options
Plus incremental shares from assumed conversions:
Incremental shares from assumed conversions				0.6		0.2	0.6

[1] For the quarter ended June 30, 2020, the dilutive impact of outstanding options and restricted stock units was excluded from the dilutive share count as a result of the Company’s net loss for the period.