Pre-Tax Effects of Derivative Instruments Recognized in OCI (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]
Gain (loss) recognized in OCI	$ 24.4	$ 54.4	$ (27.9)
Expense (income) reclassified out of AOCI into income	(21.7)	(36.0)	19.3
Interest Rate Contract | Financial Services
Derivative [Line Items]
Gain (loss) recognized in OCI	24.4	54.4	(27.9)
Interest Rate Contract | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
Expense (income) reclassified out of AOCI into income	(21.7)	(36.0)	19.3
Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	1.7	(1.2)	(1.3)
Expense (income) reclassified out of AOCI into income	(1.8)	0.4	3.4
Foreign-exchange contracts | Truck, Parts and Other
Derivative [Line Items]
Gain (loss) recognized in OCI	1.7	(1.2)	(1.3)
Foreign-exchange contracts | Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
Expense (income) reclassified out of AOCI into income	0.3	1.0	3.2
Foreign-exchange contracts | Truck, Parts and Other | Interest and other expense, net
Derivative [Line Items]
Expense (income) reclassified out of AOCI into income	$ (2.1)	$ (0.6)	$ 0.2