Income Taxes - Summary of Components of Company's Income Tax Provision (Benefit) from Continuing Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current
U.S. federal	$ 4.8	$ 45.2	$ 35.1
State and local	(0.1)	11.5	11.5
Current income tax provision (benefit)	4.7	56.7	46.6
Deferred
U.S. federal	26.1	(8.1)	0.9
State and local	11.7	2.3	3.8
Deferred income tax provision (benefit)	37.8	(5.8)	4.7
Income tax provision	$ 42.5	$ 50.9	$ 51.3