Schedule of Revenues by Major Sources (Detail) - Truck, Parts and Other - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 4,737.7	$ 4,538.4	$ 15,538.8	$ 12,018.3
Trucks
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	3,452.6	3,504.0	11,837.8	9,120.0
Trucks | Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	3,258.3	3,324.0	11,253.7	8,615.7
Trucks | Revenues from extended warranties, operating leases and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	194.3	180.0	584.1	504.3
Parts Subsegment
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,260.2	1,016.2	3,632.2	2,838.5
Parts Subsegment | Parts
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,226.1	987.2	3,528.1	2,756.6
Parts Subsegment | Revenues from dealer services and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	34.1	29.0	104.1	81.9
Winch Sales and Other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 24.9	$ 18.2	$ 68.8	$ 59.8