Income Tax Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Federal Income Tax Note
Tax Cuts and Jobs Act, Measurement Period Adjustment, Income Tax Expense (Benefit)		$ 11.5
Income Taxes Receivable, Net Operating Loss, CARES Act	$ 36.5
Tax Cuts and Jobs Act of 2017, Complete Accounting, Undistributed Accumulated Earnings of Foreign Subsidiary for which Unrecognized Deferred Tax Liabilities Have Not Been Recorded	700.0
Increases for Tax Positions Related to Prior Years			$ 261.5
Less Tax Attributable to Temporary Items Included Above	(105.9)	(127.1)	(148.2)
Unrecognized Tax Benefits, Interest on Income Taxes Expense	7.8	12.8
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	20.6	12.8
Valuation Allowance on Deferred Tax Assets	14.5	28.3
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	(13.8)	9.9
Income Taxes Paid, Net	200.0	35.1	$ 139.7
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	9.3
U.S. Federal | Subsidiary Return
Federal Income Tax Note
Operating Loss Carryforwards	0.6
State and Local Jurisdiction
Federal Income Tax Note
Operating Loss Carryforwards	$ 191.0