Reclassifications Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of sales and revenues		$ 4,689.7
Income before income taxes	$ (771.4)	(608.3)
Investment income	(2.5)	4.9
Tax (benefit) expense	170.9	137.5
Net Income (Loss)	(600.5)	(470.8)
Total reclassifications out of AOCI	12.6	2.6
Derivative Contracts
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications out of AOCI	8.3	(7.9)
Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	9.2	(11.7)
Tax (benefit) expense	(0.9)	3.8
Net Income (Loss)	8.3	(7.9)
Marketable Debt Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications out of AOCI	(0.1)	(0.5)
Marketable Debt Securities | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Investment income	(0.1)	(0.6)
Tax (benefit) expense		0.1
Net Income (Loss)	(0.1)	(0.5)
Truck, Parts and Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net sales and revenues	(6,106.4)	(5,413.5)
Cost of sales and revenues	5,285.5
Tax (benefit) expense	170.9
Net Income (Loss)	(600.5)
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	6.9	8.5
Cost of sales and revenues	3.7	2.3
Interest and other (income), net	0.3	0.2
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	4.9
Truck, Parts and Other | Actuarial loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other (income), net	5.6	14.2
Truck, Parts and Other | Prior service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other (income), net	0.1	0.2
Truck, Parts and Other | Settlement Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes	5.7	14.4
Tax (benefit) expense	(1.3)	(3.4)
Net Income (Loss)	4.4	11.0
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	$ (6.6)	$ (22.7)