Expense (Income) Recognized in Earnings Related to Foreign-Exchange Contracts (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Interest-Rate Contracts
Derivative [Line Items]
(Income) Expense recognized in earnings	$ 0.0	$ (0.1)	$ 0.0	$ (0.1)
Foreign-exchange contracts
Derivative [Line Items]
(Income) Expense recognized in earnings	(9.3)	9.9	(3.0)	36.4
Truck, Parts and Other | Interest-Rate Contracts | Interest and other (income), net
Derivative [Line Items]
(Income) Expense recognized in earnings	0.0		0.0
Truck, Parts and Other | Interest-Rate Contracts | Cost of sales and revenues
Derivative [Line Items]
(Income) Expense recognized in earnings	0.0	0.0	0.0	0.0
Truck, Parts and Other | Interest-Rate Contracts | Interest and other borrowing expenses
Derivative [Line Items]
(Income) Expense recognized in earnings		0.0		0.0
Truck, Parts and Other | Foreign-exchange contracts | Interest and other (income), net
Derivative [Line Items]
(Income) Expense recognized in earnings	0.3		3.7
Truck, Parts and Other | Foreign-exchange contracts | Cost of sales and revenues
Derivative [Line Items]
(Income) Expense recognized in earnings	0.0	0.1	1.2	0.7
Truck, Parts and Other | Foreign-exchange contracts | Interest and other borrowing expenses
Derivative [Line Items]
(Income) Expense recognized in earnings		0.7		4.2
Financial Services | Interest-Rate Contracts | Selling, general and administrative
Derivative [Line Items]
(Income) Expense recognized in earnings	0.0	0.0	0.0	0.0
Financial Services | Interest-Rate Contracts | Interest and other borrowing expenses
Derivative [Line Items]
(Income) Expense recognized in earnings	0.0	(0.1)	0.0	(0.1)
Financial Services | Foreign-exchange contracts | Selling, general and administrative
Derivative [Line Items]
(Income) Expense recognized in earnings	(0.7)	(2.3)	0.5	(13.1)
Financial Services | Foreign-exchange contracts | Interest and other borrowing expenses
Derivative [Line Items]
(Income) Expense recognized in earnings	$ (8.9)	$ 11.4	$ (8.4)	$ 44.6