Expense (Income) Recognized in Earnings Related to Foreign-Exchange Contracts (Detail) - Foreign-exchange contracts - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivative [Line Items]
Expense (income) recognized in earnings	$ (36.5)	$ (4.5)
Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
Expense (income) recognized in earnings	1.2	0.2
Truck, Parts and Other | Interest and other (income), net
Derivative [Line Items]
Expense (income) recognized in earnings	(25.2)	1.5
Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
Expense (income) recognized in earnings	(12.0)	$ (6.2)
Financial Services | Selling, general and administrative
Derivative [Line Items]
Expense (income) recognized in earnings	$ (0.5)