Pre-Tax Effects of Derivative Instruments Recognized in OCI (Detail) - Derivative Contracts - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 55.7	$ (14.3)
Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	70.6	(16.0)
Truck, Parts and Other | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	70.6	(16.0)
Financial Services | Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 55.7	$ (14.3)