Segment Reporting Information by Segment (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Net sales and revenues		$ 4,413.2	$ 5,079.9	$ 8,713.2	$ 9,912.6
Investment income		6.4	5.3	12.1	10.4
Income (loss) before income taxes		646.2	652.2	216.6	1,213.9
Depreciation and amortization		252.9	227.3	495.4	448.4
Truck, Parts and Other
Segment Reporting Information [Line Items]
Net sales and revenues		4,115.8	4,786.1	8,126.4	9,334.1
Income (loss) before income taxes		562.5	556.1	46.9	1,023.7
Depreciation and amortization		118.1	107.0	233.2	209.1
Truck, Parts and Other | Trucks
Segment Reporting Information [Line Items]
Net sales and revenues		3,341.2	3,983.4	6,611.7	7,752.5
Income (loss) before income taxes		329.4	420.1	633.5	759.2
Depreciation and amortization		112.3	101.9	221.9	198.9
Truck, Parts and Other | Trucks | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues		3,598.0	4,228.4	7,070.4	8,209.2
Truck, Parts and Other | Trucks | Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues		(256.8)	(245.0)	(458.7)	(456.7)
Truck, Parts and Other | Parts
Segment Reporting Information [Line Items]
Net sales and revenues		756.4	776.5	1,475.9	1,529.2
Income (loss) before income taxes		133.4	145.7	268.0	284.6
Depreciation and amortization		1.9	1.6	3.5	3.1
Truck, Parts and Other | Parts | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues		769.5	788.4	1,498.8	1,552.8
Truck, Parts and Other | Parts | Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues		(13.1)	(11.9)	(22.9)	(23.6)
Truck, Parts and Other | Other
Segment Reporting Information [Line Items]
Net sales and revenues		18.2	26.2	38.8	52.4
Income (loss) before income taxes	[1]	99.7	(9.7)	(854.6)	(20.1)
Depreciation and amortization		3.9	3.5	7.8	7.1
Financial Services
Segment Reporting Information [Line Items]
Revenue		297.4	293.8	586.8	578.5
Income (loss) before income taxes		77.3	90.8	157.6	179.8
Depreciation and amortization		$ 134.8	$ 120.3	$ 262.2	$ 239.3

[1] Other includes a favorable adjustment to the European Commission charge of $109.6 in the second quarter of 2016 and an expense of $(833.0) for the first half of 2016.