Schedule of Revenues by Major Sources (Detail) - Truck, Parts and Other - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 5,416.9	$ 16,205.9
Trucks
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	4,429.4	13,250.2
Trucks | Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	4,253.6	12,702.7
Trucks | Revenues from extended warranties, operating leases and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	175.8	547.5
Parts Subsegment
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	960.1	2,868.0
Parts Subsegment | Revenues from dealer services and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	26.9	80.2
Parts Subsegment | Parts
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	933.2	2,787.8
Winch Sales and Other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 27.4	$ 87.7