Income Taxes - Net Deferred Tax Liability (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Components of Deferred Tax Assets and Liabilities [Abstract]
Deferred revenue	$ 10.4	$ 8.6
Employee benefits	103.9	101.1
Bad debt reserves	7.9	8.7
Pension	11.3	13.3
Net operating loss carryforward	27.6	21.8
Foreign tax credit	3.5	3.8
Operating lease liabilities	47.1	52.3
Investments in affiliates	17.2	13.9
Securities	124.1	189.7
Other	17.5	12.2
Deferred tax assets before valuation allowance	370.5	425.4
Valuation allowance	(27.9)	(13.7)
Deferred tax assets	342.6	411.7
Depreciable and amortizable assets	264.6	275.8
Claims and related salvage	119.2	88.5
Operating lease assets	43.2	47.7
Unremitted foreign earnings	10.9	13.2
Deferred tax liabilities	437.9	425.2
Net deferred tax liability	$ 95.3	$ 13.5