Amount of (Gain) Loss from Derivative Financial Instruments Reclassified from AOCI into Consolidated Statements of Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	$ (9.5)	$ (5.9)	$ (31.7)	$ 8.2
Financial Services
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	50.7	(34.7)	13.9	(22.1)
Fair Value Hedging | Financial Services
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	0.2	0.3	0.7	1.2
Cash Flow Hedging | Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	(8.5)	(3.6)	(27.2)	10.5
Cash Flow Hedging | Financial Services
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	50.5	(35.0)	13.2	(23.3)
Net Investment Hedging | Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	$ (1.0)	$ (2.3)	$ (4.5)	$ (2.3)