Schedule of Revenues by Major Sources (Detail) - Truck, Parts and Other - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 4,538.4	$ 6,004.2	$ 12,018.3	$ 18,408.8
Trucks
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	3,504.0	4,977.4	9,120.0	15,296.6
Trucks | Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	3,324.0	4,784.6	8,615.7	14,714.6
Trucks | Revenues from extended warranties, operating leases and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	180.0	192.8	504.3	582.0
Parts Subsegment
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,016.2	1,000.9	2,838.5	3,031.0
Parts Subsegment | Parts
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	987.2	973.2	2,756.6	2,946.0
Parts Subsegment | Revenues from dealer services and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	29.0	27.7	81.9	85.0
Winch Sales and Other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 18.2	$ 25.9	$ 59.8	$ 81.2