(Gain) Loss Recognized in Earnings Related to Foreign-Exchange Contracts (Detail) - Foreign-exchange contracts - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Derivative [Line Items]
(Gain) loss recognized in earnings	$ (5.9)	$ (36.5)
Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
(Gain) loss recognized in earnings	(0.4)	1.2
Truck, Parts and Other | Interest and other (income), net
Derivative [Line Items]
(Gain) loss recognized in earnings	(3.7)	(25.2)
Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Gain) loss recognized in earnings	$ (1.8)	(12.0)
Financial Services | Selling, general and administrative
Derivative [Line Items]
(Gain) loss recognized in earnings		$ (0.5)