Pre-Tax Effects of Derivative Instruments Recognized in Other Comprehensive Income and Earnings (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Interest Rate Contract
Derivative [Line Items]
Loss (gain) recognized in OCI	$ (19.7)	$ 5.5
Expense (income) reclassified out of accumulated other comprehensive (loss) income into income	(15.6)	2.8
Interest Rate Contract | Financial Services
Derivative [Line Items]
Loss (gain) recognized in OCI	(19.7)	5.5
Interest Rate Contract | Financial Services | Interest and other borrowing expenses (income)
Derivative [Line Items]
Expense (income) reclassified out of accumulated other comprehensive (loss) income into income	(15.6)	2.8
Foreign-exchange contracts
Derivative [Line Items]
Loss (gain) recognized in OCI	(1.6)	1.2
Expense (income) reclassified out of accumulated other comprehensive (loss) income into income	(2.5)	3.0
Foreign-exchange contracts | Truck, Parts and Other
Derivative [Line Items]
Loss (gain) recognized in OCI	(1.6)	1.2
Foreign-exchange contracts | Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
Expense (income) reclassified out of accumulated other comprehensive (loss) income into income	(2.3)	2.6
Foreign-exchange contracts | Truck, Parts and Other | Interest and other (expense) income, net
Derivative [Line Items]
Expense (income) reclassified out of accumulated other comprehensive (loss) income into income	$ (0.2)	$ 0.4