Amount of Loss (Gain) from Derivative Financial Instruments Recorded in Consolidated Statements of Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Interest-Rate Contracts
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	$ (36.3)	$ 12.1	$ (43.0)	$ (10.4)
Interest-Rate Contracts | Financial Services | Interest and other borrowing expenses
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	(36.3)	12.1	(43.0)	(10.4)
Interest-Rate Contracts | Cash Flow Hedging | Financial Services | Interest and other borrowing expenses
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	(36.5)	12.2	(43.1)	(10.5)
Interest-Rate Contracts | Fair Value Hedging | Financial Services | Interest and other borrowing expenses
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	0.2	(0.1)	0.1	0.1
Foreign-exchange contracts
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	5.6	4.0	16.7	10.4
Foreign-exchange contracts | Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	5.5	2.6	16.5	10.8
Foreign-exchange contracts | Truck, Parts and Other | Cost of sales and revenues | Not designated as hedging instruments
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	0.4	(8.6)	(0.1)	(9.0)
Foreign-exchange contracts | Truck, Parts and Other | Interest and other (income), net | Not designated as hedging instruments
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	(0.6)	3.0	1.3	1.6
Foreign-exchange contracts | Financial Services | Interest and other borrowing expenses
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	0.1	1.4	0.2	(0.4)
Foreign-exchange contracts | Financial Services | Interest and other borrowing expenses | Not designated as hedging instruments
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	0.1	1.4	0.2	(0.4)
Foreign-exchange contracts | Cash Flow Hedging | Truck, Parts and Other | Sales
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	8.2	5.1	15.1	13.6
Foreign-exchange contracts | Cash Flow Hedging | Truck, Parts and Other | Cost of sales and revenues
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	(1.0)	3.7	2.7	6.0
Foreign-exchange contracts | Cash Flow Hedging | Truck, Parts and Other | Interest and other (income), net
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss		0.1	0.3	0.3
Foreign-exchange contracts | Net Investment Hedging | Truck, Parts and Other | Interest and other (income), net
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	$ (1.5)	$ (0.7)	$ (2.8)	$ (1.7)