Income Tax Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2018
Federal Income Tax Note
Less Tax Attributable to Temporary Items Included Above	$ (42.4)	$ (63.5)	$ (84.7)
Unrecognized Tax Benefits, Interest on Income Taxes Expense	12.2	7.8	5.5
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	46.2	34.0	26.2
Valuation Allowance on Deferred Tax Assets	11.0	10.3
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	0.7	2.4
Income Taxes Paid, Net	446.0	$ 375.0	(51.0)
Tax Year 2017
Federal Income Tax Note
Increases for Tax Positions Related to Prior Years				$ 261.1
Foreign Tax Authority | Her Majesty's Revenue and Customs (HMRC)
Federal Income Tax Note
Tax Expense for Revaluation of Tax Assets and Liabilities due to Finance Bill 2019-21			$ (23.6)
State and Local Jurisdiction
Federal Income Tax Note
Operating Loss Carryforwards	$ 183.9