Earnings (Loss) per Common Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings (Loss) per Common Share
Loss from continuing operations, basic	$ (21.2)	$ (20.3)	$ (66.4)	$ (74.4)
Loss from continuing operations, diluted	(21.2)	(20.3)	(66.4)	(74.4)
Income from discontinued operations, basic	539.1	29.3	606.3	85.7
Income from discontinued operations, diluted	539.1	29.3	606.3	85.7
Net income, basic	517.9	9.0	539.9	11.3
Net income, diluted	$ 517.9	$ 9.0	$ 539.9	$ 11.3
Basic weighted-average shares	82,973,519	81,771,279	82,615,949	81,475,814
Diluted weighted-average shares	82,973,519	81,771,279	82,615,949	81,475,814
Basic and diluted (loss) per common share - continuing operations
Basic (in dollars per share)	$ (0.26)	$ (0.28)	$ (0.80)	$ (0.94)
Diluted (in dollars per share)	(0.26)	(0.28)	(0.80)	(0.94)
Basic and diluted earnings per common share - discontinued operations
Basic (in dollars per share)	6.50	0.39	7.34	1.08
Diluted (in dollars per share)	6.50	0.39	7.34	1.08
Basic and diluted earnings per common share
Basic (in dollars per share)	6.24	0.11	6.54	0.14
Diluted (in dollars per share)	$ 6.24	$ 0.11	$ 6.54	$ 0.14