Product Support Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Product Liability Contingency [Line Items]
Warranty Reserves	$ 389.7	$ 440.0
Deferred Revenues	795.8	801.4
Truck, Parts and Other
Product Liability Contingency [Line Items]
Warranty Reserves	389.7	440.0	$ 380.2	$ 298.8
Truck, Parts and Other | Accounts payable, accrued expenses and other
Product Liability Contingency [Line Items]
Warranty Reserves	245.6	270.6
Deferred Revenues	269.0	237.5
Truck, Parts and Other | Other liabilities
Product Liability Contingency [Line Items]
Warranty Reserves	144.1	169.4
Deferred Revenues	513.1	547.6
Financial Services | Accounts payable, accrued expenses and other
Product Liability Contingency [Line Items]
Deferred Revenues	5.7	6.8
Financial Services | Deferred Taxes and Other Liabilities
Product Liability Contingency [Line Items]
Deferred Revenues	$ 8.0	$ 9.5