Reclassifications Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	$ (2,378.6)	$ (1,657.9)	$ (3,099.2)
Investment income	15.5	35.9	82.3
Tax expense (benefit)	526.5	359.5	711.3
Net Income (Loss)	(1,852.1)	(1,298.4)	(2,387.9)
Total reclassifications out of AOCI	19.6	106.3	56.3
Derivative Contracts
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications out of AOCI	(24.2)	64.5	39.7
Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	(33.7)	87.6	51.7
Tax expense (benefit)	9.5	(23.1)	(12.0)
Net Income (Loss)	(24.2)	64.5	39.7
Marketable Debt Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications out of AOCI	(1.6)	(1.8)	(0.3)
Marketable Debt Securities | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Investment income	(2.1)	(2.4)	(0.4)
Tax expense (benefit)	0.5	0.6	0.1
Net Income (Loss)	(1.6)	(1.8)	(0.3)
Pension Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications out of AOCI	45.4	43.6	16.9
Truck, Parts and Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net sales and revenues	(21,834.5)	(17,154.3)	(24,119.7)
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	16.6	(4.0)	21.2
Cost of sales and revenues	(1.0)	1.7	(4.1)
Interest and other (income), net	(0.1)	(4.6)	2.1
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	0.6
Truck, Parts and Other | Actuarial loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other (income), net	58.7	44.2	20.5
Truck, Parts and Other | Prior service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other (income), net	0.8	1.5	1.4
Truck, Parts and Other | Settlement loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other (income), net		11.6
Truck, Parts and Other | Pension Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	59.5	57.3	21.9
Tax expense (benefit)	(14.1)	(13.7)	(5.0)
Net Income (Loss)	45.4	43.6	16.9
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	$ (49.8)	$ 94.5	$ 32.5