Pre-Tax Effects of Gain (Loss) on Cash Flow Hedges Recognized in OCI (Detail) - Derivative Contracts - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 19.9	$ 33.7
Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	(28.9)	0.3
Truck, Parts and Other
Derivative [Line Items]
Gain (loss) recognized in OCI	35.9
Truck, Parts and Other | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	(28.4)	2.1
Financial Services | Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	19.9	33.7
Financial Services | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ (0.5)	$ (1.8)