Schedule of Revenues by Major Sources (Detail) - Truck, Parts and Other - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 7,377.6	$ 6,106.5	$ 20,608.9	$ 19,983.0
Trucks
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	5,602.4	4,381.4	15,382.0	14,850.3
Trucks \| Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	5,291.2	4,106.2	14,488.6	14,042.4
Trucks \| Revenues from extended warranties, operating leases and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	311.2	275.2	893.4	807.9
Parts Subsegment
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,780.0	1,724.6	5,237.0	5,135.4
Parts Subsegment \| Parts
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,723.3	1,676.5	5,069.7	4,991.5
Parts Subsegment \| Revenues from dealer services and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	56.7	48.1	167.3	143.9
Intersegment Eliminations and Other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ (4.8)	$ 0.5	$ (10.1)	$ (2.7)