Segment Reporting Information by Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Revenues	$ 8,744.3	$ 8,473.3
Investment income	85.5	49.0
Total Income Before Income Taxes	1,534.5	919.0
Depreciation and amortization	235.0	221.1
Truck, Parts and Other
Segment Reporting Information [Line Items]
Net Sales and revenues	8,235.0	8,050.1
Revenues	8,235.0	8,050.1
Income (loss) before income taxes	1,335.1	721.2
Depreciation and amortization	109.4	109.8
Truck, Parts and Other | Trucks
Segment Reporting Information [Line Items]
Net Sales and revenues	6,541.0	6,413.8
Income (loss) before income taxes	881.6	894.3
Depreciation and amortization	99.6	99.8
Truck, Parts and Other | Trucks | Operating Segments
Segment Reporting Information [Line Items]
Net Sales and revenues	6,678.9	6,578.7
Truck, Parts and Other | Trucks | Intersegment
Segment Reporting Information [Line Items]
Net Sales and revenues	(137.9)	(164.9)
Truck, Parts and Other | Parts Subsegment
Segment Reporting Information [Line Items]
Net Sales and revenues	1,675.9	1,623.0
Income (loss) before income taxes	455.8	438.6
Depreciation and amortization	3.8	3.7
Truck, Parts and Other | Parts Subsegment | Operating Segments
Segment Reporting Information [Line Items]
Net Sales and revenues	1,695.3	1,641.1
Truck, Parts and Other | Parts Subsegment | Intersegment
Segment Reporting Information [Line Items]
Net Sales and revenues	(19.4)	(18.1)
Truck, Parts and Other | Other
Segment Reporting Information [Line Items]
Net Sales and revenues	18.1	13.3
Income (loss) before income taxes	(2.3)	(611.7)
Depreciation and amortization	6.0	6.3
Financial Services
Segment Reporting Information [Line Items]
Revenues	509.3	423.2
Income (loss) before income taxes	113.9	148.8
Depreciation and amortization	$ 125.6	$ 111.3