Expense (Income) Recognized in Earnings Related to Foreign-Exchange Contracts (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Interest-Rate Contracts
Derivative [Line Items]
(Income) Expense recognized in earnings	$ 0.0	$ 0.1	$ (0.1)	$ 0.1
Interest-Rate Contracts | Cost of sales and revenues
Derivative [Line Items]
(Income) Expense recognized in earnings		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	0.0
Foreign-exchange contracts
Derivative [Line Items]
(Income) Expense recognized in earnings	4.4	(5.4)	48.7	(13.3)
Foreign-exchange contracts | Cost of sales and revenues
Derivative [Line Items]
(Income) Expense recognized in earnings		0.3		1.4
Foreign-exchange contracts | Interest and other expense, net
Derivative [Line Items]
(Income) Expense recognized in earnings	(1.0)	(1.3)	3.2	(0.5)
Truck, Parts and Other | Interest-Rate Contracts | Cost of sales and revenues
Derivative [Line Items]
(Income) Expense recognized in earnings	0.0		0.0
Truck, Parts and Other | Interest-Rate Contracts | Net sales and revenues
Derivative [Line Items]
(Income) Expense recognized in earnings		0.0		0.0
Truck, Parts and Other | Foreign-exchange contracts | Cost of sales and revenues
Derivative [Line Items]
(Income) Expense recognized in earnings	0.6		1.3
Truck, Parts and Other | Foreign-exchange contracts | Net sales and revenues
Derivative [Line Items]
(Income) Expense recognized in earnings		(0.4)		(0.4)
Financial Services | Interest-Rate Contracts | Interest and other borrowing expenses
Derivative [Line Items]
(Income) Expense recognized in earnings	0.0	0.1	(0.1)	0.1
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 | Foreign-exchange contracts | Interest and other borrowing expenses
Derivative [Line Items]
(Income) Expense recognized in earnings	4.8	(3.1)	43.4	(11.3)
Financial Services | Foreign-exchange contracts | Selling, general and administrative
Derivative [Line Items]
(Income) Expense recognized in earnings	$ 0.0	$ (0.9)	$ 0.8	$ (2.5)