Segment Reporting Information by Segment (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Revenues	$ 5,161.7	$ 6,487.6
Income (loss) before income taxes:	462.2	819.4
Investment income	14.8	19.3
Depreciation and amortization	272.0	259.1
Truck, Parts and Other
Segment Reporting Information [Line Items]
Net sales and revenues	4,778.0	6,138.1
Income (loss) before income taxes:	399.1	716.1
Depreciation and amortization	90.8	104.1
Truck, Parts and Other \| Trucks
Segment Reporting Information [Line Items]
Net sales and revenues	3,757.6	5,107.3
Income (loss) before income taxes:	183.1	517.0
Depreciation and amortization	83.2	97.4
Truck, Parts and Other \| Trucks \| Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues	3,863.2	5,226.6
Truck, Parts and Other \| Trucks \| Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues	(105.6)	(119.3)
Truck, Parts and Other \| Parts Subsegment
Segment Reporting Information [Line Items]
Net sales and revenues	998.6	1,004.7
Income (loss) before income taxes:	214.7	207.6
Depreciation and amortization	2.5	2.7
Truck, Parts and Other \| Parts Subsegment \| Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues	1,010.7	1,016.0
Truck, Parts and Other \| Parts Subsegment \| Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues	(12.1)	(11.3)
Truck, Parts and Other \| Other
Segment Reporting Information [Line Items]
Net sales and revenues	21.8	26.1
Income (loss) before income taxes:	1.3	(8.5)
Depreciation and amortization	5.1	4.0
Financial Services
Segment Reporting Information [Line Items]
Revenues	383.7	349.5
Income (loss) before income taxes:	48.3	84.0
Depreciation and amortization	$ 181.2	$ 155.0

The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

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