Components of Provision for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current provision
Federal	$ 19.1	$ 34.7	$ 219.8
State	11.9	12.8	30.3
Current Income Tax Expense (Benefit), Total	31.0	47.5	250.1
Deferred provision (benefit)
Federal	18.0	17.6	(180.4)
State	(6.8)	(2.0)	(21.5)
Deferred taxes	11.2	15.6	(201.9)
Total provision for income taxes	$ 42.2	$ 63.1	$ 48.2