Amount of (Income) Expense from Derivative Financial Instruments Recognized in Consolidated Statements of Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	$ (1.3)	$ 3.2	$ 12.8	$ 0.7
Financial Services
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	(34.7)	(3.3)	(22.1)	(85.2)
Fair Value Hedging | Financial Services
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	0.3	0.4	1.2	1.3
Cash Flow Hedging | Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	(3.6)	3.2	10.5	0.7
Cash Flow Hedging | Financial Services
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	(35.0)	(3.7)	(23.3)	(86.5)
Net Investment Hedging | Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments expense (income)	$ 2.3	$ 0.0	$ 2.3	$ 0.0