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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Interest-Rate Contracts
Derivative [Line Items]
Reclassification from AOCIinto income	$ (92.1)	$ 40.0	$ (82.8)	$ 85.8
Foreign-exchange contracts
Derivative [Line Items]
Reclassification from AOCIinto income	(5.0)	11.4	(2.5)	15.7
Cash Flow Hedging | Interest-Rate Contracts | Truck, Parts and Other | Sales
Derivative [Line Items]
Reclassification from AOCIinto income	0.0	0.0	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	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	0.0	0.0
Cash Flow Hedging | Interest-Rate Contracts | Financial Services | Interest and other borrowing expenses
Derivative [Line Items]
Reclassification from AOCIinto income	(92.1)	40.0	(82.8)	85.8
Cash Flow Hedging | Foreign-exchange contracts | Truck, Parts and Other | Sales
Derivative [Line Items]
Reclassification from AOCIinto income	(2.8)	12.1	1.8	16.3
Cash Flow Hedging | Foreign-exchange contracts | Truck, Parts and Other | Cost of sales and revenues
Derivative [Line Items]
Reclassification from AOCIinto income	(2.5)	(1.3)	(3.6)	(1.2)
Cash Flow Hedging | Foreign-exchange contracts | Truck, Parts and Other | Interest and other (income), net
Derivative [Line Items]
Reclassification from AOCIinto income	0.3	0.6	(0.7)	0.6
Cash Flow Hedging | Foreign-exchange contracts | Financial Services
Derivative [Line Items]
Reclassification from AOCIinto income	0.0	0.0	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	$ 0.0	$ 0.0