Schedule of Revenues by Major Sources (Detail) - Truck, Parts and Other - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 5,413.5	$ 4,778.0
Trucks
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	4,233.0	3,757.6
Trucks | Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	4,045.0	3,583.6
Trucks | Revenues from extended warranties, operating leases and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	188.0	174.0
Parts Subsegment
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,160.7	998.6
Parts Subsegment | Parts
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,125.9	970.0
Parts Subsegment | Revenues from dealer services and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	34.8	28.6
Winch Sales and Other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 19.8	$ 21.8