Reclassifications Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	$ (1,589.4)	$ (979.7)	$ (4,076.9)	$ (2,673.2)
Investment income	80.8	21.4	192.5	24.3
Tax (benefit) expense	360.9	210.3	893.4	582.9
Net Income (Loss)	(1,228.5)	(769.4)	(3,183.5)	(2,090.3)
Reclassified out of AOCI	(26.9)	(32.9)	38.4	(30.2)
Derivative Contracts
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassified out of AOCI	(27.7)	(38.2)	37.0	(46.5)
Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	(36.8)	(52.5)	42.2	(67.1)
Tax (benefit) expense	9.1	14.3	(5.2)	20.6
Net Income (Loss)	(27.7)	(38.2)	37.0	(46.5)
Marketable Debt Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassified out of AOCI	(0.4)	(0.3)	(2.1)	(0.6)
Marketable Debt Securities | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Investment income	(0.5)	(0.4)	(2.8)	(0.8)
Tax (benefit) expense	0.1	0.1	0.7	0.2
Net Income (Loss)	(0.4)	(0.3)	(2.1)	(0.6)
Truck, Parts and Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net sales and revenues	(8,232.3)	(6,687.0)	(24,723.7)	(19,579.6)
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	13.2	2.0	25.2	17.1
Cost of sales and revenues	(9.6)	(6.2)	1.8	(3.5)
Interest and other (income) expense, net	(0.9)	3.9	(0.9)	8.8
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	4.2	7.0	1.8	17.4
Truck, Parts and Other | Actuarial loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other (income) expense, net	1.2	7.1	3.6	21.7
Truck, Parts and Other | Prior service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other (income) expense, net	0.3	0.2	1.0	0.5
Truck, Parts and Other | Settlement Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	1.5	7.3	4.6	22.2
Tax (benefit) expense	(0.3)	(1.7)	(1.1)	(5.3)
Net Income (Loss)	1.2	5.6	3.5	16.9
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	(1.6)	(3.0)	(3.6)	(7.6)
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	$ (42.1)	$ (56.2)	$ 17.9	$ (99.3)