Expense or (Income) Recognized in Earnings Related to Economic Hedges (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest Rate Contract
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges		$ (1.5)	$ 1.0
Interest Rate Contract | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges		(1.5)	1.0
Foreign-exchange contracts
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	7.9	(10.6)	(0.2)
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	(5.3)	(1.3)	(0.3)
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	3.8	0.3	(0.5)
Foreign-exchange contracts | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	4.2	(9.6)	0.6
Foreign-exchange contracts | Financial Services | SG&A
Derivative [Line Items]
(Income) or expense recognized in earnings related to economic hedges	$ 5.2