Expense or (Income) Recognized in Earnings Related to Economic Hedges (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Interest Rate Contract
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	$ (0.3)	$ (0.1)		$ (1.5)
Interest Rate Contract | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	(0.3)	(0.1)		(1.5)
Foreign-exchange contracts
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	(9.7)	(5.2)	(4.9)	(9.0)
Foreign-exchange contracts | Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	(3.8)	(1.3)	(4.0)	(0.9)
Foreign-exchange contracts | Truck, Parts and Other | Interest and other expense, net
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	1.9	0.4	2.2	0.8
Foreign-exchange contracts | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	$ (7.8)	$ (4.3)	$ (3.1)	$ (8.9)