Expenses (Income) Recognized in Earnings Related to Foreign-Exchange Contracts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest-Rate Contracts
Derivative [Line Items]
(Income) expense recognized in earnings			$ (0.1)
Interest-Rate Contracts | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Income) expense recognized in earnings			(0.1)
Foreign-exchange contracts
Derivative [Line Items]
(Income) expense recognized in earnings	$ (4.1)	$ (6.6)	52.0
Foreign-exchange contracts | Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
(Income) expense recognized in earnings	0.5	(0.3)	0.3
Foreign-exchange contracts | Truck, Parts and Other | Other Nonoperating Income (Expense)
Derivative [Line Items]
(Income) expense recognized in earnings	5.4	6.9	2.1
Foreign-exchange contracts | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Income) expense recognized in earnings	(10.1)	(14.9)	49.1
Foreign-exchange contracts | Financial Services | Selling, general and administrative
Derivative [Line Items]
(Income) expense recognized in earnings	$ 0.1	$ 1.7	$ 0.5