Reclassifications Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	$ (5,718.2)	$ (3,848.7)	$ (2,396.3)
Investment income	292.2	61.0	15.5
Tax (benefit) expense	1,117.4	837.1	530.8
Net Income (Loss)	(4,600.8)	(3,011.6)	(1,865.5)
Reclassified out of AOCI	93.7	61.3	19.6
Derivative Contracts
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassified out of AOCI	91.8	40.0	(24.2)
Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	111.8	48.0	(33.7)
Tax (benefit) expense	(20.0)	(8.0)	9.5
Net Income (Loss)	91.8	40.0	(24.2)
Marketable Debt Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassified out of AOCI	(2.7)	(1.2)	(1.6)
Marketable Debt Securities | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Investment income	(3.6)	(1.6)	(2.1)
Tax (benefit) expense	0.9	0.4	0.5
Net Income (Loss)	(2.7)	(1.2)	(1.6)
Pension Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassified out of AOCI	4.6	22.5	45.4
Truck, Parts and Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net sales and revenues	(33,315.5)	(27,314.3)	(21,834.5)
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	31.9	19.3	16.6
Cost of sales and revenues	2.2	(15.3)	(1.0)
Interest and other expenses (income), net	(0.9)	(1.4)	(0.1)
Truck, Parts and Other | Derivative Contracts | Commodity contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of sales and revenues	4.2	32.0	0.6
Truck, Parts and Other | Actuarial loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other expenses (income), net	4.7	28.9	58.7
Truck, Parts and Other | Prior service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other expenses (income), net	1.4	0.7	0.8
Truck, Parts and Other | Settlement loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	6.1	29.6	59.5
Tax (benefit) expense	(1.5)	(7.1)	(14.1)
Net Income (Loss)	4.6	22.5	45.4
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	(2.1)	7.3
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	$ 76.5	$ 6.1	$ (49.8)