Schedule of Revenues by Major Sources (Detail) - Truck, Parts and Other - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ 6,997.0	$ 6,962.8	$ 13,231.3	$ 13,876.5
Trucks
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	5,253.1	5,243.1	9,779.6	10,468.9
Trucks \| Truck Sales
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	4,958.3	4,964.5	9,197.4	9,936.2
Trucks \| Revenues from extended warranties, operating leases and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	294.8	278.6	582.2	532.7
Parts Subsegment
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,746.9	1,720.9	3,457.0	3,410.8
Parts Subsegment \| Parts
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	1,690.3	1,677.4	3,346.4	3,315.0
Parts Subsegment \| Revenues from dealer services and other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	56.6	43.5	110.6	95.8
Intersegment Eliminations and Other
Entity Wide Information Revenue From External Customer [Line Items]
Total sales and revenues	$ (3.0)	$ (1.2)	$ (5.3)	$ (3.2)