Segment Reporting Information by Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenues	$ 23,522.3	$ 18,728.5	$ 25,599.7
Investment income	15.5	35.9	82.3
Total Income Before Income Taxes	2,378.6	1,657.9	3,099.2
Depreciation and amortization	903.3	1,049.0	1,077.3
Expenditures for long-lived assets	1,585.5	1,657.5	2,140.7
Assets	29,301.7	28,260.0	28,361.1
Truck, Parts and Other
Segment Reporting Information [Line Items]
Net sales and revenues	21,834.5	17,154.3	24,119.7
Revenues	21,834.5	17,154.3	24,119.7
Income (loss) before income taxes	1,925.5	1,398.9	2,718.0
Depreciation and amortization	311.5	323.8	412.4
Expenditures for long-lived assets	600.7	610.8	762.1
Assets	13,882.8	12,460.2	12,289.7
Cash and marketable securities	4,813.0	4,834.0	5,169.4
Truck, Parts and Other | Trucks
Segment Reporting Information [Line Items]
Net sales and revenues	16,799.7	13,164.8	19,989.5
Income (loss) before income taxes	795.8	581.4	1,904.9
Depreciation and amortization	277.6	292.2	381.9
Expenditures for long-lived assets	547.2	556.0	664.9
Assets	6,912.1	5,971.9	5,609.0
Truck, Parts and Other | Trucks | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues	17,379.0	13,643.0	20,403.5
Truck, Parts and Other | Trucks | Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues	(579.3)	(478.2)	(414.0)
Truck, Parts and Other | Parts Subsegment
Segment Reporting Information [Line Items]
Net sales and revenues	4,944.3	3,912.9	4,024.9
Income (loss) before income taxes	1,104.1	799.3	830.8
Depreciation and amortization	12.0	10.8	10.2
Expenditures for long-lived assets	29.4	18.4	46.2
Assets	1,505.1	1,255.6	1,172.1
Truck, Parts and Other | Parts Subsegment | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues	5,004.8	3,962.7	4,073.1
Truck, Parts and Other | Parts Subsegment | Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues	(60.5)	(49.8)	(48.2)
Truck, Parts and Other | Other
Segment Reporting Information [Line Items]
Net sales and revenues	90.5	76.6	105.3
Income (loss) before income taxes	25.6	18.2	(17.7)
Depreciation and amortization	21.9	20.8	20.3
Expenditures for long-lived assets	24.1	36.4	51.0
Assets	652.6	398.7	339.2
Financial Services
Segment Reporting Information [Line Items]
Revenues	1,687.8	1,574.2	1,480.0
Income (loss) before income taxes	437.6	223.1	298.9
Depreciation and amortization	591.8	725.2	664.9
Expenditures for long-lived assets	984.8	1,046.7	1,378.6
Assets	$ 15,418.9	$ 15,799.8	$ 16,071.4