Loss (Gain) Recognized in Earnings to Derivatives not Designated as Hedging Instruments (Detail) - Foreign-exchange contracts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
(Gain) loss recognized in earnings	$ 13.2	$ (4.1)	$ (6.6)
Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
(Gain) loss recognized in earnings	0.7	0.5	(0.3)
Truck, Parts and Other | Interest and other (income), net
Derivative [Line Items]
(Gain) loss recognized in earnings	2.3	5.4	6.9
Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Gain) loss recognized in earnings	9.4	(10.1)	(14.9)
Financial Services | Selling, general and administrative
Derivative [Line Items]
(Gain) loss recognized in earnings	$ 0.8	$ 0.1	$ 1.7