Schedule of Revenues by Major Sources (Detail) - Truck, Parts and Other - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 6,004.2	$ 5,416.9	$ 18,408.8	$ 16,205.9
Trucks
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	4,977.4	4,429.4	15,296.6	13,250.2
Trucks | Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	4,784.6	4,253.6	14,714.6	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	192.8	175.8	582.0	547.5
Parts Subsegment
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,000.9	960.1	3,031.0	2,868.0
Parts Subsegment | Parts
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	973.2	933.2	2,946.0	2,787.8
Parts Subsegment | Revenues from dealer services and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	27.7	26.9	85.0	80.2
Winch Sales and Other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 25.9	$ 27.4	$ 81.2	$ 87.7