Expense (Income) Recognized in Earnings Related to Economic Hedges (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Interest-Rate Contracts
Derivative [Line Items]
Expense (Income) recognized in earnings		$ (0.3)
Interest-Rate Contracts | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
Expense (Income) recognized in earnings		(0.3)
Foreign-exchange contracts
Derivative [Line Items]
Expense (Income) recognized in earnings	$ (6.7)	(9.7)	$ (12.7)	$ (4.9)
Foreign-exchange contracts | Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
Expense (Income) recognized in earnings	(0.8)	(3.8)	0.6	(4.0)
Foreign-exchange contracts | Truck, Parts and Other | Interest and other expense, net
Derivative [Line Items]
Expense (Income) recognized in earnings	(4.9)	1.9	(4.1)	2.2
Foreign-exchange contracts | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
Expense (Income) recognized in earnings	(0.3)	$ (7.8)	(7.8)	$ (3.1)
Foreign-exchange contracts | Financial Services | Selling, general and administrative
Derivative [Line Items]
Expense (Income) recognized in earnings	$ (0.7)		$ (1.4)