Pre-Tax Effects of Derivative Instruments Recognized in OCI (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Interest Rate Contract
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 28.7	$ (33.1)	$ (1.6)	$ 41.3
Expense (income) reclassified out of AOCI into income	(23.6)	32.8	8.0	(29.1)
Interest Rate Contract | Financial Services
Derivative [Line Items]
Gain (loss) recognized in OCI	28.7	(33.1)	(1.6)	41.3
Interest Rate Contract | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
Expense (income) reclassified out of AOCI into income	(23.6)	32.8	8.0	(29.1)
Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	2.5	(4.6)	(0.3)	(1.7)
Expense (income) reclassified out of AOCI into income	(0.1)	1.3	1.8	(0.7)
Foreign-exchange contracts | Truck, Parts and Other
Derivative [Line Items]
Gain (loss) recognized in OCI	2.5	(4.6)	(0.3)	(1.7)
Foreign-exchange contracts | Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
Expense (income) reclassified out of AOCI into income	(0.1)	1.8	1.7	(0.5)
Foreign-exchange contracts | Truck, Parts and Other | Interest and other expense, net
Derivative [Line Items]
Expense (income) reclassified out of AOCI into income		$ (0.5)	$ 0.1	$ (0.2)