Income Tax Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2019
Federal Income Tax Note
Less Tax Attributable to Temporary Items Included Above	$ 0.0	$ (21.2)	$ (42.4)
Unrecognized Tax Benefits, Interest on Income Taxes Expense	11.2	13.2	12.2
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	70.6	59.4	46.2
Operating Loss Carryforwards	61.2
Valuation Allowance on Deferred Tax Assets	11.5	12.1
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	0.6	1.1
Income Taxes Paid, Net	93.7	376.0	446.0
Deferred Tax Assets, Tax Credit Carryforwards	101.2	0.0
Income Tax Paid, Federal, after Refund Received	78.2	377.0	402.3
Income Tax Paid, Foreign, after Refund Received	17.1	8.4	36.7
Income Tax Paid, State and Local, after Refund Received	(1.6)	$ (9.4)	7.0
Capital Loss Carryforward	135.2
Tax Year 2017
Federal Income Tax Note
Increases for Tax Positions Related to Prior Years				$ 261.1
State and Local Jurisdiction
Federal Income Tax Note
Operating Loss Carryforwards	186.7
UNITED KINGDOM
Federal Income Tax Note
Income Tax Paid, Foreign, after Refund Received	$ 15.9		$ 34.4