Pre-Tax Effects of Gain (Loss) on Cash Flow Hedges Recognized in OCI (Detail) - Derivative Contracts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 83.2	$ (107.3)	$ (44.4)
Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	(20.4)	2.0	(31.7)
Truck, Parts and Other | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	(18.5)	2.8	(31.7)
Financial Services | Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	83.2	(107.3)	$ (44.4)
Financial Services | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ (1.9)	$ (0.8)