Pre-Tax Effects of Derivative Instruments Recognized in OCI (Detail) - Derivative Contracts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest-Rate Contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	$ (44.4)	$ 117.1	$ (108.1)
Foreign-exchange contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	(31.7)	4.5	(17.4)
Truck, Parts and Other | Foreign-exchange contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	(31.7)	4.5	(17.4)
Financial Services | Interest-Rate Contracts
Derivative [Line Items]
(Loss) gain recognized in OCI	$ (44.4)	$ 117.1	$ (108.1)