Schedule of Revenues by Major Sources (Detail) - Truck, Parts and Other - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 5,932.7	$ 5,416.9	$ 5,467.2	$ 5,321.8	$ 5,122.4	$ 4,731.5	$ 4,397.9	$ 3,935.7	$ 22,138.6	$ 18,187.5	$ 15,846.6
Trucks
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues									18,187.0	14,774.8	12,767.3
Trucks | Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues									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									739.2
Parts Subsegment
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues									3,838.9	$ 3,327.0	$ 3,005.7
Parts Subsegment | Parts
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues									3,731.9
Parts Subsegment | Revenues from dealer services and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues									107.0
Winch Sales and Other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues									$ 112.7