Location and Amount of (Income)/Expense for the Cash Flow and Fair Value Hedges Reclassified from AOCI into Income (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Interest-Rate Contracts
Derivative [Line Items]
Reclassification from AOCIinto income	$ (3,700,000)	$ 24,600,000	$ (86,500,000)	$ 110,400,000
Foreign-exchange contracts
Derivative [Line Items]
Reclassification from AOCIinto income	3,200,000	3,500,000	700,000	19,200,000
Cash Flow Hedging | Interest-Rate Contracts | Truck, Parts and Other | Sales
Derivative [Line Items]
Reclassification from AOCIinto income	0	0	0	0
Cash Flow Hedging | Interest-Rate Contracts | Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
Reclassification from AOCIinto income	0	0	0	0
Cash Flow Hedging | Interest-Rate Contracts | Truck, Parts and Other | Interest and other (income), net
Derivative [Line Items]
Reclassification from AOCIinto income	0	0	0	0
Cash Flow Hedging | Interest-Rate Contracts | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
Reclassification from AOCIinto income	(3,700,000)	24,600,000	(86,500,000)	110,400,000
Cash Flow Hedging | Foreign-exchange contracts | Truck, Parts and Other | Sales
Derivative [Line Items]
Reclassification from AOCIinto income	4,300,000	(3,000,000)	6,100,000	13,300,000
Cash Flow Hedging | Foreign-exchange contracts | Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
Reclassification from AOCIinto income	(1,600,000)	5,500,000	(5,200,000)	4,300,000
Cash Flow Hedging | Foreign-exchange contracts | Truck, Parts and Other | Interest and other (income), net
Derivative [Line Items]
Reclassification from AOCIinto income	500,000	1,000,000	(200,000)	1,600,000
Cash Flow Hedging | Foreign-exchange contracts | Financial Services
Derivative [Line Items]
Reclassification from AOCIinto income	0	0	0	0
Cash Flow Hedging | Foreign-exchange contracts | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
Reclassification from AOCIinto income	$ 0	$ 0	$ 0	$ 0