Pre-Tax Effects of Derivative Instruments Recognized in OCI (Detail) - Derivative Contracts - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 26.0	$ 2.9		$ 84.5
Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	(1.0)	(11.3)	$ (17.2)	(4.9)
Truck, Parts and Other | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	(1.0)	(11.3)	$ (17.2)	(4.9)
Financial Services | Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 26.0	$ 2.9		$ 84.5