Expenses (Income) Recognized in Earnings Related to Foreign-Exchange Contracts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest-Rate Contracts
Derivative [Line Items]
(Income) Expense recognized in earnings	$ (0.1)	$ 0.1	$ 0.0
Interest-Rate Contracts | Cost of sales and revenues
Derivative [Line Items]
(Income) Expense recognized in earnings	0.0	0.0	0.0
Interest-Rate Contracts | Interest and other expense, net
Derivative [Line Items]
(Income) Expense recognized in earnings	0.0	0.0	0.0
Interest-Rate Contracts | Truck, Parts and Other | Net sales and revenues
Derivative [Line Items]
(Income) Expense recognized in earnings	0.0	0.0	0.0
Interest-Rate Contracts | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Income) Expense recognized in earnings	(0.1)	0.1	0.0
Interest-Rate Contracts | Financial Services | Selling, general and administrative
Derivative [Line Items]
(Income) Expense recognized in earnings	0.0	0.0	0.0
Foreign-exchange contracts
Derivative [Line Items]
(Income) Expense recognized in earnings	52.0	(11.7)	(7.6)
Foreign-exchange contracts | Cost of sales and revenues
Derivative [Line Items]
(Income) Expense recognized in earnings	0.3	0.4	(0.7)
Foreign-exchange contracts | Interest and other expense, net
Derivative [Line Items]
(Income) Expense recognized in earnings	2.1	14.9	3.0
Foreign-exchange contracts | Truck, Parts and Other | Net sales and revenues
Derivative [Line Items]
(Income) Expense recognized in earnings	0.0	(0.4)	0.0
Foreign-exchange contracts | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Income) Expense recognized in earnings	49.1	(28.4)	(7.6)
Foreign-exchange contracts | Financial Services | Selling, general and administrative
Derivative [Line Items]
(Income) Expense recognized in earnings	$ 0.5	$ 1.8	$ (2.3)