Pre-Tax Effects of (Loss) Gain on Cash Flow Hedges Recognized in OCI (Detail) - Derivative Contracts - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Interest-Rate Contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	$ (72.0)	$ 24.7
Foreign-exchange contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	(20.4)	16.2
Commodity contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	(0.2)	(4.6)
Truck, Parts and Other | Foreign-exchange contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	(11.3)	13.5
Truck, Parts and Other | Commodity contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	(0.2)	(4.6)
Financial Services | Interest-Rate Contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	(72.0)	24.7
Financial Services | Foreign-exchange contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	$ (9.1)	$ 2.7