Pre-Tax Effects of Gain (Loss) on Cash Flow Hedges Recognized in OCI (Detail) - Derivative Contracts - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 44.9	$ 49.4	$ (33.0)	$ 109.1
Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	35.3	35.3	(30.3)	35.1
Commodity Contract
Derivative [Line Items]
Gain (loss) recognized in OCI	(4.8)	(7.9)	(2.9)	(15.7)
Truck, Parts and Other | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	33.7	35.4	(33.5)	35.5
Truck, Parts and Other | Commodity Contract
Derivative [Line Items]
Gain (loss) recognized in OCI	(4.8)	(7.9)	(2.9)	(15.7)
Financial Services | Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	44.9	49.4	(33.0)	109.1
Financial Services | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 1.6	$ (0.1)	$ 3.2	$ (0.4)