Pre-Tax Effects of Derivative Instruments Recognized in OCI (Detail) - Derivative Contracts - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ (11.7)	$ 93.1	$ (26.0)	$ 81.6
Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	(0.2)	10.8	(16.2)	6.4
Truck, Parts and Other | Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	(0.2)	10.8	(16.2)	6.4
Financial Services | Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ (11.7)	$ 93.1	$ (26.0)	$ 81.6