Pre-Tax Effects of Derivative Instruments Recognized in Earnings and Other Comprehensive (Loss) Income (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]
(Gain)/loss recognized in OCI	$ 5.7	$ 2.6	$ 29.4	$ 31.2
(Income)/expense reclassified from Accumulated OCI into income	1.6	(16.3)	17.7	20.2
Interest Rate Contract | Financial Services
Derivative [Line Items]
(Gain)/loss recognized in OCI	5.7	2.6	29.4	31.2
Interest Rate Contract | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
(Income)/expense reclassified from Accumulated OCI into income	1.6	(16.3)	17.7	20.2
Foreign-exchange contracts
Derivative [Line Items]
(Gain)/loss recognized in OCI	1.3	1.8	2.2	(5.9)
(Income)/expense reclassified from Accumulated OCI into income	2.0	(0.7)	4.7	(3.3)
Foreign-exchange contracts | Truck and Other
Derivative [Line Items]
(Gain)/loss recognized in OCI	1.3	1.8	2.2	(5.9)
Foreign-exchange contracts | Truck and Other | Cost of sales and revenues
Derivative [Line Items]
(Income)/expense reclassified from Accumulated OCI into income	1.6	(0.7)	4.3	(3.3)
Foreign-exchange contracts | Truck and Other | Interest and other (expense) income, net
Derivative [Line Items]
(Income)/expense reclassified from Accumulated OCI into income	$ 0.4		$ 0.4