Balance Sheet Classification of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Deferred Income Tax Assets And Liabilities [Line Items]
Deferred Tax Liabilities	$ (590.5)	$ (532.4)
Truck, Parts and Other | Other Noncurrent Assets
Schedule Of Deferred Income Tax Assets And Liabilities [Line Items]
Deferred Tax Assets Net	115.4	97.1
Truck, Parts and Other | Other liabilities
Schedule Of Deferred Income Tax Assets And Liabilities [Line Items]
Deferred Tax Liabilities	(5.3)	(2.5)
Financial Services | Other Assets
Schedule Of Deferred Income Tax Assets And Liabilities [Line Items]
Deferred Tax Assets Net	36.8	37.7
Financial Services | Deferred Taxes and Other Liabilities
Schedule Of Deferred Income Tax Assets And Liabilities [Line Items]
Deferred Tax Liabilities	$ (737.4)	$ (664.7)