Schedule of Income subject to domestic and foreign taxation (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax [Abstract]
Income Before Tax, Domestic	$ 957.0	$ 924.7	$ 1,289.5
Income Before Tax, Foreign	106.0	39.3	92.6
Income Before Income Tax	1,063.0	964.0	1,382.1
Current Tax Expense (Benefit), Domestic	180.7	(98.4)	273.6
Current State and Local Tax Expense (Benefit)	2.6	1.5	1.3
Current Tax Expense (Benefit), Foreign	29.5	(19.7)	(0.1)
Income Tax (Benefit) - Current	212.8	(116.6)	274.8
Deferred Tax Expense (Benefit), Federal	13.3	250.5	(9.5)
Deferred State and Local Income Tax Expense (Benefit)	(2.2)	1.0	(0.1)
Deferred Tax Expense (Benefit), Foreign	14.9	36.1	16.6
Deferred Income Tax Expense (Benefit)	26.0	287.6	7.0
Income Tax Expense	$ 238.8	$ 171.0	$ 281.8