Product Support Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Product Liability Contingency [Line Items]
Warranty Reserves	$ 298.8	$ 282.1
Deferred Revenues	653.9	573.5
Truck, Parts and Other
Product Liability Contingency [Line Items]
Warranty Reserves	298.8	282.1	$ 346.2	$ 310.8
Deferred Revenues	653.9	573.5	$ 524.8	$ 462.0
Truck, Parts and Other | Accounts payable, accrued expenses and other
Product Liability Contingency [Line Items]
Warranty Reserves	176.0	181.4
Deferred Revenues	196.1	162.8
Truck, Parts and Other | Other liabilities
Product Liability Contingency [Line Items]
Warranty Reserves	122.8	100.7
Deferred Revenues	441.0	395.7
Financial Services | Deferred Taxes And Other Liabilities
Product Liability Contingency [Line Items]
Warranty Reserves	0.0	0.0
Deferred Revenues	$ 16.8	$ 15.0