Schedule of Revenues by Major Sources (Detail) - Truck, Parts and Other - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 5,387.6	$ 2,701.9	$ 10,801.1	$ 7,479.9
Trucks
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	4,152.2	1,858.4	8,385.2	5,616.0
Trucks | Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	3,950.4	1,708.1	7,995.4	5,291.7
Trucks | Revenues from extended warranties, operating leases and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	201.8	150.3	389.8	324.3
Parts Subsegment
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,211.3	823.7	2,372.0	1,822.3
Parts Subsegment | Parts
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,176.1	799.4	2,302.0	1,769.4
Parts Subsegment | Revenues from dealer services and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	35.2	24.3	70.0	52.9
Winch Sales and Other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 24.1	$ 19.8	$ 43.9	$ 41.6