Schedule of Income subject to domestic and foreign taxation (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income Tax [Abstract]
Income Before Tax, Domestic	$ 803.7	$ 2,129.5	$ 1,506.2
Income Before Tax, Foreign	129.8	121.8	133.9
Income Before Income Tax	933.5	2,251.3	1,640.1
Current Tax Expense (Benefit), Domestic	53.6	393.1	440.4
Current State and Local Tax Expense (Benefit)	1.1	(8.5)	(2.5)
Current Tax Expense (Benefit), Foreign	17.0	47.5	14.1
Income Tax (Benefit) - Current	71.7	432.1	452.0
Deferred Tax Expense (Benefit), Federal	112.0	59.8	(106.2)
Deferred State and Local Income Tax Expense (Benefit)	0.9	(0.6)	(1.5)
Deferred Tax Expense (Benefit), Foreign	10.4	(19.1)	12.0
Deferred Income Tax Expense (Benefit)	123.3	40.1	(95.7)
Income Tax Expense	$ 195.0	$ 472.2	$ 356.3