(Gain) Loss Recognized in Earnings Related to Foreign-Exchange Contracts (Detail) - Foreign-exchange contracts - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative [Line Items]
(Gain) loss recognized in earnings	$ 6.2	$ (5.5)	$ (20.8)	$ (7.6)
Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
(Gain) loss recognized in earnings	(0.8)	0.8	0.4	0.8
Truck, Parts and Other | Interest and other (income), net
Derivative [Line Items]
(Gain) loss recognized in earnings		2.0	(19.3)	4.6
Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Gain) loss recognized in earnings	6.9	$ (8.3)	$ (1.9)	$ (13.0)
Financial Services | Selling, general and administrative
Derivative [Line Items]
(Gain) loss recognized in earnings	$ 0.1