Schedule of Revenues by Major Sources (Detail) - Truck, Parts and Other - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 6,266.5	$ 5,467.2	$ 12,404.6	$ 10,789.0
Trucks
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	5,211.9	4,467.8	10,319.2	8,820.8
Trucks | Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	5,016.4	4,274.7	9,930.0	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	195.5	193.1	389.2	371.7
Parts Subsegment
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,025.4	968.0	2,030.1	1,907.9
Parts Subsegment | Parts
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	996.2	942.5	1,972.8	1,854.6
Parts Subsegment | Revenues from dealer services and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	29.2	25.5	57.3	53.3
Winch Sales and Other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 29.2	$ 31.4	$ 55.3	$ 60.3