Schedule of Revenues by Major Sources (Detail) - Truck, Parts and Other - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 6,962.8	$ 8,262.3	$ 13,876.5	$ 16,497.3
Trucks
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	5,243.1	6,577.8	10,468.9	13,118.8
Trucks \| Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	4,964.5	6,337.6	9,936.2	12,642.3
Trucks \| Revenues from extended warranties, operating leases and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	278.6	240.2	532.7	476.5
Parts Subsegment
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,720.9	1,664.3	3,410.8	3,340.2
Parts Subsegment \| Parts
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,677.4	1,614.0	3,315.0	3,239.6
Parts Subsegment \| Revenues from dealer services and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	43.5	50.3	95.8	100.6
Intersegment Eliminations and Other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ (1.2)	$ 20.2	$ (3.2)	$ 38.3