Schedule of Revenues by Major Sources (Detail) - Truck, Parts and Other - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 5,710.9	$ 6,004.2	$ 6,266.5	$ 6,138.1	$ 5,932.7	$ 5,416.9	$ 5,467.2	$ 5,321.8	$ 24,119.7	$ 22,138.6
Trucks
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues									19,989.5	18,187.0
Trucks | Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues									19,225.2	17,447.8
Trucks | Revenues from extended warranties, operating leases and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues									764.3	739.2
Parts Subsegment
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues									4,024.9	3,838.9
Parts Subsegment | Parts
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues									3,912.1	3,731.9
Parts Subsegment | Revenues from dealer services and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues									112.8	107.0
Winch Sales and Other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues									$ 105.3	$ 112.7