Income Taxes - Components of Income Tax Expense From Continuing Operations (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Federal income taxes:
Current	$ 264.0	$ 174.9	$ 66.3
Deferred	(11.4)	18.0	61.4
Total federal income taxes	252.6	192.9	127.7
State income taxes:
Current	42.7	35.1	18.7
Deferred	(3.0)	5.3	6.5
Total state income taxes	39.7	40.4	25.2
Foreign income taxes:
Current	0.2	1.2	0.0
Deferred	0.0	0.3	0.3
Total foreign income taxes	0.2	1.5	0.3
Income tax expense	$ 292.5	$ 234.8	$ 153.2