Schedule of Revenues by Major Sources (Detail) - Truck, Parts and Other - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 5,467.2	$ 10,789.0
Trucks
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	4,467.8	8,820.8
Trucks | Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	4,274.7	8,449.1
Trucks | Revenues from extended warranties, operating leases and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	193.1	371.7
Parts Subsegment
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	968.0	1,907.9
Parts Subsegment | Revenues from dealer services and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	25.5	53.3
Parts Subsegment | Parts
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	942.5	1,854.6
Winch Sales and Other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 31.4	$ 60.3