Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Expense Benefit [Line Items]
Interest expense, domestic deposits	$ 40.1	$ 65.8	$ 64.2
Net unrecognized tax benefits	9.4	8.8
Accrued interest and penalties related to unrecognized tax benefits	$ 3.1	2.9
Open tax year	2011 2012
Deferred tax liabilities	$ 490.8	445.3
Undistributed earnings of foreign subsidiaries	$ 574.0	$ 631.0
Federal statutory rate	21.00%	21.00%	35.00%
Deferred income taxes	$ 945.6	$ 806.2
Noncurrent Liabilities [Member]
Income Tax Expense Benefit [Line Items]
Deferred tax liabilities	127.5	106.9
Deferred minimum tax credits	14.3
General Business Tax Credits [Member]
Income Tax Expense Benefit [Line Items]
Deferred tax credits	$ 937.2
Deferred tax credits expiration year	2034
State Tax Credits [Member]
Income Tax Expense Benefit [Line Items]
Deferred tax credits	$ 10.6
Deferred tax credits expiration year	2023
HR One [Member]
Income Tax Expense Benefit [Line Items]
Deferred income taxes		2.9	$ 1.0
U.S. repatriation tax rate			10.00%
U.S. repatriation tax amount		$ 2.9	$ 40.0