Amount of Expense (Income) from Derivative Financial Instruments Recognized in Consolidated Statements of Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	$ 23.8	$ (2.8)	$ 17.8
Financial Services
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	34.0	(116.9)	116.4
Cash Flow Hedging | Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	19.2	(2.8)	17.8
Cash Flow Hedging | Financial Services
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	32.5	(118.7)	115.6
Net Investment Hedging | Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	4.6
Fair Value Hedging | Financial Services
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	$ 1.5	$ 1.8	$ 0.8