Pre-Tax Effects of Derivative Instruments Recognized in OCI (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Interest-Rate Contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	$ 33.8	$ 24.4	$ 54.4
Expense (income) reclassified out of AOCI into income	(28.5)	(21.7)	(36.0)
Interest-Rate Contracts | Financial Services
Derivative [Line Items]
Gain (loss) recognized in OCI	33.8	24.4	54.4
Interest-Rate Contracts | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
Expense (income) reclassified out of AOCI into income	(28.5)	(21.7)	(36.0)
Foreign-exchange contracts
Derivative [Line Items]
Gain (loss) recognized in OCI	4.9	1.7	(1.2)
Expense (income) reclassified out of AOCI into income	(0.8)	(1.8)	0.4
Foreign-exchange contracts | Truck, Parts and Other
Derivative [Line Items]
Gain (loss) recognized in OCI	4.9	1.7	(1.2)
Foreign-exchange contracts | Truck, Parts and Other | Net sales and revenues
Derivative [Line Items]
Expense (income) reclassified out of AOCI into income	(0.1)
Foreign-exchange contracts | Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
Expense (income) reclassified out of AOCI into income	3.4	0.3	1.0
Foreign-exchange contracts | Truck, Parts and Other | Interest and other expenses, net
Derivative [Line Items]
Expense (income) reclassified out of AOCI into income	$ (4.1)	$ (2.1)	$ (0.6)