Segment Reporting Information by Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Revenues	$ 28,819.7	$ 23,522.3	$ 18,728.5
Investment income	61.0	15.5	35.9
Total Income Before Income Taxes	3,848.7	2,396.3	1,661.6
Depreciation and amortization	790.2	903.3	1,049.0
Expenditures for long-lived assets	1,370.5	1,585.5	1,657.5
Assets	33,275.5	29,509.4	28,450.0
Truck, Parts and Other
Segment Reporting Information [Line Items]
Net sales and revenues	27,314.3	21,834.5	17,154.3
Revenues	27,314.3	21,834.5	17,154.3
Income (loss) before income taxes	3,198.8	1,943.2	1,402.6
Depreciation and amortization	362.8	311.5	323.8
Expenditures for long-lived assets	515.7	600.7	610.8
Assets	16,095.9	14,090.5	12,650.2
Cash and marketable securities	6,158.9	4,813.0	4,834.0
Truck, Parts and Other | Trucks
Segment Reporting Information [Line Items]
Net sales and revenues	21,486.2	16,799.7	13,164.8
Income (loss) before income taxes	1,753.3	804.9	578.2
Depreciation and amortization	324.9	277.6	292.2
Expenditures for long-lived assets	466.0	547.2	556.0
Assets	7,218.1	6,912.1	5,971.9
Truck, Parts and Other | Trucks | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues	22,005.5	17,379.0	13,643.0
Truck, Parts and Other | Trucks | Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues	(519.3)	(579.3)	(478.2)
Truck, Parts and Other | Parts Subsegment
Segment Reporting Information [Line Items]
Net sales and revenues	5,764.3	4,944.3	3,912.9
Income (loss) before income taxes	1,446.6	1,110.0	802.0
Depreciation and amortization	14.0	12.0	10.8
Expenditures for long-lived assets	21.1	29.4	18.4
Assets	1,742.1	1,505.1	1,255.6
Truck, Parts and Other | Parts Subsegment | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues	5,829.4	5,004.8	3,962.7
Truck, Parts and Other | Parts Subsegment | Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues	(65.1)	(60.5)	(49.8)
Truck, Parts and Other | Other
Segment Reporting Information [Line Items]
Net sales and revenues	63.8	90.5	76.6
Income (loss) before income taxes	(1.1)	28.3	22.4
Depreciation and amortization	23.9	21.9	20.8
Expenditures for long-lived assets	28.6	24.1	36.4
Assets	976.8	860.3	588.7
Financial Services
Segment Reporting Information [Line Items]
Revenues	1,505.4	1,687.8	1,574.2
Income (loss) before income taxes	588.9	437.6	223.1
Depreciation and amortization	427.4	591.8	725.2
Expenditures for long-lived assets	854.8	984.8	1,046.7
Assets	$ 17,179.6	$ 15,418.9	$ 15,799.8