Schedule of Revenues by Major Sources (Detail) - Truck, Parts and Other - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 6,106.5	$ 7,703.8	$ 19,983.0	$ 24,201.1
Trucks
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	4,381.4	6,027.0	14,850.3	19,145.8
Trucks \| Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	4,106.2	5,781.2	14,042.4	18,423.5
Trucks \| Revenues from extended warranties, operating leases and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	275.2	245.8	807.9	722.3
Parts Subsegment
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,724.6	1,657.6	5,135.4	4,997.8
Parts Subsegment \| Parts
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,676.5	1,605.0	4,991.5	4,844.6
Parts Subsegment \| Revenues from dealer services and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	48.1	52.6	143.9	153.2
Intersegment Eliminations and Other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 0.5	$ 19.2	$ (2.7)	$ 57.5