Pre-Tax Effects of Gain (Loss) on Cash Flow Hedges Recognized in OCI (Detail) - Derivative Contracts - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 24.7	$ (42.3)
Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	16.2	(21.1)
Commodity contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	(4.6)	(3.9)
Truck, Parts and Other | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	13.5	(20.1)
Truck, Parts and Other | Commodity contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	(4.6)	(3.9)
Financial Services | Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	24.7	(42.3)
Financial Services | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 2.7	$ (1.0)