Income Taxes - Income Tax (Benefit) Provision Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Current income tax provision (benefit) related to:
United States (Federal)	$ 35.4	$ 28.0	$ 37.3
United States (State)	2.4	1.4	1.7
United Kingdom	(2.2)	(0.1)	(1.5)
Other jurisdictions	1.6	0.0	0.1
Total current income tax provision	37.2	29.3	37.6
Deferred income tax provision (benefit) related to:
United States	(26.3)	(5.1)	(17.7)
United Kingdom	(12.3)	(16.6)	(5.8)
Other jurisdictions	0.0	0.1	0.0
Total deferred income tax (benefit)	(38.6)	(21.6)	(23.5)
Income tax provision (benefit)	$ (1.4)	$ 7.7	$ 14.1