Amount of Loss (Gain) from Derivative Financial Instruments Recorded in Consolidated Statements of Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Interest-Rate Contracts
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	$ (35.4)	$ 50.7	$ (45.8)	$ 13.9
Interest-Rate Contracts | Financial Services | Interest and other borrowing expenses
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	(35.4)	50.7	(45.8)	13.9
Foreign-exchange contracts
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	13.5	(3.3)	23.9	(52.5)
Foreign-exchange contracts | Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	13.8	(10.3)	24.6	(50.6)
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	17.8	(0.8)	8.8	0.4
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)		1.0	(19.3)
Foreign-exchange contracts | Financial Services | Interest and other borrowing expenses
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	(0.3)	7.0	(0.7)	(1.9)
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	(0.3)	6.9	(0.7)	(1.9)
Foreign-exchange contracts | Financial Services | Selling, General and Administrative Expenses
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss		0.1
Fair Value Hedging | Interest-Rate Contracts | Financial Services | Interest and other borrowing expenses
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss		0.2	0.1	0.7
Cash Flow Hedging | Interest-Rate Contracts | Financial Services | Interest and other borrowing expenses
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	(35.4)	50.5	(45.9)	13.2
Cash Flow Hedging | Foreign-exchange contracts | Truck, Parts and Other | Net sales and revenues
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	1.3	(10.6)	14.9	(22.2)
Cash Flow Hedging | Foreign-exchange contracts | Truck, Parts and Other | Cost of sales and revenues
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	(3.5)	2.5	2.5	0.2
Cash Flow Hedging | Foreign-exchange contracts | Truck, Parts and Other | Interest and other (income), net
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	(0.5)	(0.4)	(0.2)	(5.2)
Net Investment Hedging | Foreign-exchange contracts | Truck, Parts and Other | Interest and other (income), net
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	$ (0.7)	$ (1.0)	$ (2.4)	$ (4.5)