Pre-Tax Effects of Derivative Instruments Recognized in OCI (Detail) - Derivative Contracts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ (30.9)	$ 33.8	$ 24.4
Interest-Rate Contracts | Truck, Parts and Other
Derivative [Line Items]
Gain (loss) recognized in OCI	0.0	0.0	0.0
Interest-Rate Contracts | Financial Services
Derivative [Line Items]
Gain (loss) recognized in OCI	(30.9)	33.8	24.4
Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	24.4	4.9	1.7
Foreign-exchange contracts | Truck, Parts and Other
Derivative [Line Items]
Gain (loss) recognized in OCI	24.4	4.9	1.7
Foreign-exchange contracts | Financial Services
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 0.0	$ 0.0	$ 0.0