Expense or (Income) Recognized in Earnings Related to Economic Hedges (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Interest Rate Contract
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	$ (1.3)	$ 1.0
Interest Rate Contract | Financial Services | Interest and other borrowing expenses (income)
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	(1.3)	1.0
Foreign-exchange contracts
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	1.9	(0.9)
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	(0.1)
Foreign-exchange contracts | Truck, Parts and Other | Interest and other (expense) income, net
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	1.7	(0.6)
Foreign-exchange contracts | Financial Services | Interest and other borrowing expenses (income)
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	$ 0.3	$ (0.3)