Segment Reporting Information by Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Revenues	$ 33,663.8	$ 35,127.4	$ 28,819.7
Cost of sales and revenues	26,069.6	26,894.2	23,291.0
Research and development	452.9	410.9	341.2
Selling, general and administrative	744.0	753.3	726.3
Interest and other borrowing expenses	710.8	500.6	216.3
Depreciation and other expenses	718.5	590.7	560.8
Provision for losses on receivables	75.6	31.3	5.5
Other segment (income) expenses	(113.8)	520.4	(109.1)
Income (Loss) before investment income and income taxes	5,006.2	5,426.0	3,787.7
Investment income	394.7	292.2	61.0
Total Income Before Income Taxes	5,400.9	5,718.2	3,848.7
Depreciation and amortization	916.9	923.9	790.2
Expenditures for long-lived assets	1,702.7	1,265.9	1,370.5
Assets	43,418.9	40,823.4	33,275.5
Operating Segments
Segment Reporting Information [Line Items]
Revenues	34,177.1	35,610.2	29,404.1
Intersegment
Segment Reporting Information [Line Items]
Revenues	(513.3)	(482.8)	(584.4)
Truck, Parts and Other
Segment Reporting Information [Line Items]
Net sales and revenues	31,564.3	33,315.5	27,314.3
Revenues	31,564.3	33,315.5	27,314.3
Cost of sales and revenues	26,069.6	26,894.2	23,291.0
Research and development	452.9	410.9	341.2
Selling, general and administrative	585.0	604.3	592.4
Other segment (income) expenses	(113.8)	520.4	(109.1)
Income (Loss) before investment income and income taxes	4,570.6	4,885.7	3,198.8
Total Income Before Income Taxes	4,570.6	4,885.7	3,198.8
Depreciation and amortization	413.5	443.8	362.8
Expenditures for long-lived assets	815.0	683.7	515.7
Assets	21,007.4	19,859.5	16,095.9
Cash and marketable securities	9,649.9	8,659.3	6,158.9
Truck, Parts and Other | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues	32,077.6	33,798.3	27,898.7
Truck, Parts and Other | Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues	(513.3)	(482.8)	(584.4)
Truck, Parts and Other | Truck
Segment Reporting Information [Line Items]
Net sales and revenues	24,838.4	26,846.4	21,486.2
Cost of sales and revenues	21,389.8	22,440.6	19,205.4
Research and development	343.6	306.6	246.1
Selling, general and administrative	254.2	278.5	280.0
Other segment (income) expenses	(1.8)	20.8	1.4
Income (Loss) before investment income and income taxes	2,852.6	3,799.9	1,753.3
Total Income Before Income Taxes	2,852.6	3,799.9	1,753.3
Depreciation and amortization	374.0	403.5	324.9
Expenditures for long-lived assets	711.4	584.8	466.0
Assets	7,563.3	8,038.5	7,218.1
Truck, Parts and Other | Truck | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues	25,274.2	27,257.1	22,005.5
Truck, Parts and Other | Truck | Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues	(435.8)	(410.7)	(519.3)
Truck, Parts and Other | Parts
Segment Reporting Information [Line Items]
Net sales and revenues	6,666.4	6,414.4	5,764.3
Cost of sales and revenues	4,604.4	4,369.6	4,009.6
Research and development	108.7	103.5	94.6
Selling, general and administrative	246.4	238.0	216.3
Other segment (income) expenses	2.4	0.7	(2.8)
Income (Loss) before investment income and income taxes	1,704.5	1,702.6	1,446.6
Total Income Before Income Taxes	1,704.5	1,702.6	1,446.6
Depreciation and amortization	14.8	15.0	14.0
Expenditures for long-lived assets	52.2	65.7	21.1
Assets	2,097.0	1,912.1	1,742.1
Truck, Parts and Other | Parts | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues	6,743.9	6,486.5	5,829.4
Truck, Parts and Other | Parts | Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues	(77.5)	(72.1)	(65.1)
Truck, Parts and Other | Other
Segment Reporting Information [Line Items]
Net sales and revenues	59.5	54.7	63.8
Cost of sales and revenues	75.4	84.0	76.0
Research and development	0.6	0.8	0.5
Selling, general and administrative	84.4	87.8	96.1
Other segment (income) expenses	(114.4)	498.9	(107.7)
Income (Loss) before investment income and income taxes	13.5	(616.8)	(1.1)
Total Income Before Income Taxes	13.5	(616.8)	(1.1)
Depreciation and amortization	24.7	25.3	23.9
Expenditures for long-lived assets	51.4	33.2	28.6
Assets	1,697.2	1,249.6	976.8
Truck, Parts and Other | Other | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues	59.5	54.7	63.8
Financial Services
Segment Reporting Information [Line Items]
Revenues	2,099.5	1,811.9	1,505.4
Selling, general and administrative	159.0	149.0	133.9
Interest and other borrowing expenses	710.8	500.6	216.3
Depreciation and other expenses	718.5	590.7	560.8
Provision for losses on receivables	75.6	31.3	5.5
Income (Loss) before investment income and income taxes	435.6	540.3	588.9
Total Income Before Income Taxes	435.6	540.3	588.9
Depreciation and amortization	503.4	480.1	427.4
Expenditures for long-lived assets	887.7	582.2	854.8
Assets	22,411.5	20,963.9	17,179.6
Financial Services | Operating Segments
Segment Reporting Information [Line Items]
Revenues	$ 2,099.5	$ 1,811.9	$ 1,505.4