Pre-Tax Effects of Gain (Loss) on Cash Flow Hedges Recognized in OCI (Detail) - Derivative Contracts - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ (35.6)	$ 39.8	$ (77.9)	$ 59.7
Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	(44.5)	28.7	(65.6)	(0.2)
Commodity Contract
Derivative [Line Items]
Gain (loss) recognized in OCI	(2.0)	(43.7)	1.9	(7.8)
Truck, Parts and Other | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	(47.1)	28.5	(67.2)	0.1
Truck, Parts and Other | Commodity Contract
Derivative [Line Items]
Gain (loss) recognized in OCI	(2.0)	(43.7)	1.9	(7.8)
Financial Services | Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	(35.6)	39.8	(77.9)	59.7
Financial Services | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 2.6	$ 0.2	$ 1.6	$ (0.3)