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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 39.8	$ (10.0)	$ 59.7	$ 23.7
Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	28.7	(12.2)	(0.2)	(11.9)
Commodity Contract
Derivative [Line Items]
Gain (loss) recognized in OCI	(43.7)		(7.8)
Truck, Parts and Other | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	28.5	(11.1)	0.1	(9.0)
Truck, Parts and Other | Commodity Contract
Derivative [Line Items]
Gain (loss) recognized in OCI	(43.7)		(7.8)
Financial Services | Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	39.8	(10.0)	59.7	23.7
Financial Services | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 0.2	$ (1.1)	$ (0.3)	$ (2.9)