Amount of (Income) Expense from Derivative Financial Instruments Recognized in Consolidated Statements of Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	$ (4.7)	$ 7.8
Financial Services
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	(67.4)	7.3
Fair Value Hedging | Financial Services
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	0.3	0.6
Cash Flow Hedging | Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	(7.2)	7.8
Cash Flow Hedging | Financial Services
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	(67.7)	$ 6.7
Net Investment Hedging | Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	$ 2.5