Segment Reporting Information by Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Net sales and revenues	$ 4,300.0	$ 4,832.7
Investment income	5.7	5.1
Income (loss) before income taxes	(429.6)	561.7
Depreciation and amortization	242.5	221.1
Truck, Parts and Other
Segment Reporting Information [Line Items]
Net sales and revenues	4,010.6	4,548.0
Income (loss) before income taxes	(515.6)	467.6
Depreciation and amortization	115.1	102.1
Truck, Parts and Other | Trucks
Segment Reporting Information [Line Items]
Net sales and revenues	3,270.5	3,769.1
Income (loss) before income taxes	304.1	339.1
Depreciation and amortization	109.6	97.0
Truck, Parts and Other | Trucks | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues	3,472.4	3,980.8
Truck, Parts and Other | Trucks | Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues	(201.9)	(211.7)
Truck, Parts and Other | Parts
Segment Reporting Information [Line Items]
Net sales and revenues	719.5	752.7
Income (loss) before income taxes	134.6	138.9
Depreciation and amortization	1.6	1.5
Truck, Parts and Other | Parts | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues	729.3	764.4
Truck, Parts and Other | Parts | Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues	(9.8)	(11.7)
Truck, Parts and Other | Other
Segment Reporting Information [Line Items]
Net sales and revenues	20.6	26.2
Income (loss) before income taxes	(954.3)	(10.4)
Depreciation and amortization	3.9	3.6
Financial Services
Segment Reporting Information [Line Items]
Revenue	289.4	284.7
Income (loss) before income taxes	80.3	89.0
Depreciation and amortization	$ 127.4	$ 119.0