Location and Amount of (Income)/Expense for the Cash Flow and Fair Value Hedges Reclassified from AOCI into Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Interest-Rate Contracts
Derivative [Line Items]
Reclassification from AOCIinto income	$ 9.3	$ 45.8
Foreign-exchange contracts
Derivative [Line Items]
Reclassification from AOCIinto income	2.5	4.3
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	9.3	45.8
Cash Flow Hedging | Foreign-exchange contracts | Truck, Parts and Other | Sales
Derivative [Line Items]
Reclassification from AOCIinto income	4.6	4.2
Cash Flow Hedging | Foreign-exchange contracts | Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
Reclassification from AOCIinto income	(1.1)	0.1
Cash Flow Hedging | Foreign-exchange contracts | Truck, Parts and Other | Interest and other (income), net
Derivative [Line Items]
Reclassification from AOCIinto income	(1.0)	0.0
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