Reclassifications Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	$ (919.0)	$ (771.4)
Investment income	49.0	(2.5)
Tax (benefit) expense	185.1	170.9
Net Income (Loss)	(733.9)	(600.5)
Reclassified out of AOCI	23.1	12.6
Derivative Contracts
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassified out of AOCI	23.2	8.3
Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	29.9	9.2
Tax (benefit) expense	(6.7)	(0.9)
Net Income (Loss)	23.2	8.3
Marketable Debt Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassified out of AOCI	(0.8)	(0.1)
Marketable Debt Securities | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Investment income	(1.1)	(0.1)
Tax (benefit) expense	0.3
Net Income (Loss)	(0.8)	(0.1)
Truck, Parts and Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net sales and revenues	(8,050.1)	(6,106.4)
Truck, Parts and Other | Derivative Contracts | Foreign-exchange contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net sales and revenues	0.2	6.9
Cost of sales and revenues		3.7
Interest and other expenses (income), net	(0.7)	0.3
Truck, Parts and Other | Derivative Contracts | Commodity Contract | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of sales and revenues	2.2	4.9
Truck, Parts and Other | Actuarial loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other expenses (income), net	0.7	5.6
Truck, Parts and Other | Prior service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other expenses (income), net	0.3	0.1
Truck, Parts and Other | Settlement Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	1.0	5.7
Tax (benefit) expense	(0.3)	(1.3)
Net Income (Loss)	0.7	4.4
Financial Services | Derivative Contracts | Foreign-exchange contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other borrowing expenses	0.8
Financial Services | Derivative Contracts | Interest-Rate Contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other borrowing expenses	$ 27.4	$ (6.6)