Income Taxes - Income Tax (Benefit) Provision Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Current income tax provision (benefit) related to:
United States (Federal)	$ (21.0)	$ 35.4	$ 28.0
United States (State)	0.1	2.4	1.4
United Kingdom	(0.8)	(2.2)	(0.1)
Other jurisdictions	(1.7)	1.6	0.0
Total current income tax provision	(23.4)	37.2	29.3
Deferred income tax provision (benefit) related to:
United States	6.0	(26.3)	(5.1)
United Kingdom	7.3	(12.3)	(16.6)
Other jurisdictions	2.1	0.0	0.1
Total deferred income tax (benefit)	15.4	(38.6)	(21.6)
Income tax provision (benefit)	$ (8.0)	$ (1.4)	$ 7.7