Schedule of Revenues by Major Sources (Detail) - Truck, Parts and Other $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 5,321.8
Trucks
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	4,353.0
Trucks | Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	4,174.4
Trucks | Revenues from extended warranties, operating leases and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	178.6
Parts Subsegment
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	939.9
Parts Subsegment | Revenues from dealer services and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	27.8
Parts Subsegment | Parts
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	912.1
Winch Sales and Other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 28.9