Pre-Tax Effects of Derivative Instruments Recognized in OCI (Detail) - Derivative Contracts - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Interest-Rate Contracts
Derivative [Line Items]
Loss recognized in OCI	$ (14.3)	$ (11.5)
Foreign-exchange contracts
Derivative [Line Items]
Loss recognized in OCI	(16.0)	(4.4)
Truck, Parts and Other | Foreign-exchange contracts
Derivative [Line Items]
Loss recognized in OCI	(16.0)	(4.4)
Financial Services | Interest-Rate Contracts
Derivative [Line Items]
Loss recognized in OCI	$ (14.3)	$ (11.5)