Product Support Liabilities - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($)
Product Warranty Liability [Line Items]
Deferred revenue on extended warranties and R&M recognize, in 2020	$ 67.5
Deferred revenue on extended warranties and R&M recognize, in 2021	266.5
Deferred revenue on extended warranties and R&M recognize, in 2022	230.5
Deferred revenue on extended warranties and R&M recognize, in 2023	131.4
Deferred revenue on extended warranties and R&M recognize, in 2024	57.8
Deferred revenue on extended warranties and R&M recognize, thereafter	$ 24.7
Truck, Parts and Other
Product Warranty Liability [Line Items]
Standard product warranty, description	The Company generally offers one year warranties covering most of its vehicles and related aftermarket parts. For vehicles equipped with engines manufactured by PACCAR, the Company generally offers two year warranties on the engine.
Standard product warranty, term	1 year
Extended product warranty, description	Optional extended warranty and R&M contracts can be purchased for periods which generally range up to five years.
Truck, Parts and Other | Maximum
Product Warranty Liability [Line Items]
Extended product warranty, term	5 years
Truck, Parts and Other | Engines manufactured by PACCAR
Product Warranty Liability [Line Items]
Standard product warranty, term	2 years