Pre-Tax Effects of Gain (Loss) on Cash Flow Hedges Recognized in OCI (Detail) - Derivative Contracts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 176.9	$ (110.5)	$ 19.1
Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	98.1	(63.9)	15.7
Truck, Parts and Other | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	88.9	(65.7)	41.2
Financial Services | Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	176.9	(110.5)	19.1
Financial Services | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 9.2	$ 1.8	$ (25.5)