Pre-Tax Effects of (Loss) Gain on Cash Flow Hedges Recognized in OCI (Detail) - Derivative Contracts - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Interest-Rate Contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	$ (54.9)	$ 44.9	$ 26.7	$ (33.0)
Foreign-exchange contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	(4.5)	35.3	47.6	(30.3)
Commodity contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	(0.6)	(4.8)	(13.6)	(2.9)
Truck, Parts and Other | Foreign-exchange contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	0.1	33.7	47.1	(33.5)
Truck, Parts and Other | Commodity contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	(0.6)	(4.8)	(13.6)	(2.9)
Financial Services | Interest-Rate Contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	(54.9)	44.9	26.7	(33.0)
Financial Services | Foreign-exchange contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	$ (4.6)	$ 1.6	$ 0.5	$ 3.2