(Income) or Expense Recognized in Earnings Related to Economic Hedges (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Interest Rate Contract
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	$ 1.6	$ (5.0)	$ 1.5	$ (5.0)
Interest Rate Contract | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	1.6	(5.0)	1.5	(5.0)
Foreign-exchange contracts
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	1.5	(0.7)	(0.1)	(1.8)
Foreign-exchange contracts | Truck and Other | Cost of sales and revenues
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges		0.1	(0.3)	0.1
Foreign-exchange contracts | Truck and Other | Interest and other (expense) income, net
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	2.0	(0.3)	(0.4)	(0.3)
Foreign-exchange contracts | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	$ (0.5)	$ (0.5)	$ 0.6	$ (1.6)