Income Taxes - Components of Income Tax Expense From Continuing Operations (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Federal income taxes:
Current	$ 66.3	$ 91.9	$ 83.9
Deferred	61.4	45.4	31.1
Total federal income taxes	127.7	137.3	115.0
State income taxes:
Current	18.7	21.0	20.5
Deferred	6.5	8.7	(1.5)
Total state income taxes	25.2	29.7	19.0
Foreign income taxes:
Current		1.2	2.8
Deferred	0.3		(0.5)
Total foreign income taxes	0.3	1.2	2.3
Income tax expense	$ 153.2	$ 168.2	$ 136.3