Product Support Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Product Liability Contingency [Line Items]
Warranty Reserves	$ 380.2	$ 298.8
Deferred Revenues	699.9	653.9
Truck, Parts and Other
Product Liability Contingency [Line Items]
Warranty Reserves	380.2	298.8	$ 282.1	$ 346.2
Deferred Revenues	699.9	653.9	$ 573.5	$ 524.8
Truck, Parts and Other | Accounts payable, accrued expenses and other
Product Liability Contingency [Line Items]
Warranty Reserves	233.0	176.0
Deferred Revenues	213.7	196.1
Truck, Parts and Other | Other liabilities
Product Liability Contingency [Line Items]
Warranty Reserves	147.2	122.8
Deferred Revenues	468.8	441.0
Financial Services | Deferred Taxes And Other Liabilities
Product Liability Contingency [Line Items]
Warranty Reserves	0.0	0.0
Deferred Revenues	$ 17.4	$ 16.8