Segment Reporting Information by Segment (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Net sales and revenues		$ 4,704.2	$ 4,413.2	$ 8,942.1	$ 8,713.2
Investment income		8.7	6.4	16.8	12.1
Income (loss) before income taxes		539.0	646.2	987.2	216.6
Depreciation and amortization		269.0	252.9	528.2	495.4
Truck, Parts and Other
Segment Reporting Information [Line Items]
Net sales and revenues		4,397.9	4,115.8	8,333.6	8,126.4
Income (loss) before income taxes		467.3	562.5	850.1	46.9
Depreciation and amortization		117.2	118.1	230.0	233.2
Truck, Parts and Other | Trucks
Segment Reporting Information [Line Items]
Net sales and revenues		3,553.6	3,341.2	6,683.7	6,611.7
Income (loss) before income taxes		323.7	329.4	565.4	633.5
Depreciation and amortization		111.0	112.3	218.1	221.9
Truck, Parts and Other | Trucks | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues		3,768.9	3,598.0	7,066.2	7,070.4
Truck, Parts and Other | Trucks | Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues		(215.3)	(256.8)	(382.5)	(458.7)
Truck, Parts and Other | Parts
Segment Reporting Information [Line Items]
Net sales and revenues		823.1	756.4	1,609.8	1,475.9
Income (loss) before income taxes		152.4	133.4	304.1	268.0
Depreciation and amortization		2.0	1.9	3.9	3.5
Truck, Parts and Other | Parts | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues		835.2	769.5	1,634.3	1,498.8
Truck, Parts and Other | Parts | Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues		(12.1)	(13.1)	(24.5)	(22.9)
Truck, Parts and Other | Other
Segment Reporting Information [Line Items]
Net sales and revenues		21.2	18.2	40.1	38.8
Income (loss) before income taxes	[1]	(8.8)	99.7	(19.4)	(854.6)
Depreciation and amortization		4.2	3.9	8.0	7.8
Financial Services
Segment Reporting Information [Line Items]
Revenue		306.3	297.4	608.5	586.8
Income (loss) before income taxes		63.0	77.3	120.3	157.6
Depreciation and amortization		$ 151.8	$ 134.8	$ 298.2	$ 262.2

[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.