Amount of Loss (Gain) from Derivative Financial Instruments Recorded in Consolidated Statements of Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	$ 10.0	$ (9.7)
Financial Services
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	(22.5)	(67.4)
Fair Value Hedging | Financial Services
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	0.2	0.3
Cash Flow Hedging | Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	11.0	(7.2)
Cash Flow Hedging | Financial Services
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	(22.7)	(67.7)
Net Investment Hedging | Truck, Parts and Other
Derivative Instruments Gain Loss [Line Items]
Derivatives designated as hedging instruments (gain) loss	$ (1.0)	$ (2.5)