Segment Reporting Information by Segment (Detail) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net sales and revenues										$ 17,033.3	$ 19,115.1	$ 18,997.0
Investment income										27.6	21.8	22.3
Income before income taxes										1,130.4	2,337.1	2,017.6
Depreciation and amortization										993.1	907.1	917.7
Assets		$ 20,638.9				$ 21,109.8				20,638.9	21,109.8	20,618.8
Expenditures for long-lived assets										1,992.4	1,747.0	1,462.2
Truck, Parts and Other
Segment Reporting Information [Line Items]
Net sales and revenues		3,767.0	$ 3,953.2	$ 4,115.8	$ 4,010.6	4,062.5	$ 4,546.2	$ 4,786.1	$ 4,548.0	15,846.6	17,942.8	17,792.8
Income before income taxes										796.3	1,952.7	1,624.9
Cash and marketable securities		2,922.6				3,378.0				2,922.6	3,378.0	2,937.1
Depreciation and amortization										455.9	420.9	432.7
Assets		8,444.1				8,855.2				8,444.1	8,855.2	8,701.5
Expenditures for long-lived assets										778.0	702.6	526.9
Truck, Parts and Other | Trucks
Segment Reporting Information [Line Items]
Net sales and revenues										12,767.3	14,782.5	14,594.0
Income before income taxes										1,125.8	1,440.3	1,160.1
Depreciation and amortization										432.8	399.8	415.0
Assets		4,429.4				4,472.3				4,429.4	4,472.3	4,871.1
Expenditures for long-lived assets										735.6	660.0	504.9
Truck, Parts and Other | Trucks | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues										13,652.7	15,568.6	15,330.4
Truck, Parts and Other | Trucks | Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues										(885.4)	(786.1)	(736.4)
Truck, Parts and Other | Parts
Segment Reporting Information [Line Items]
Net sales and revenues										3,005.7	3,060.1	3,077.5
Income before income taxes										543.8	555.6	496.7
Depreciation and amortization										7.3	6.2	5.9
Assets		805.1				793.3				805.1	793.3	787.2
Expenditures for long-lived assets										16.9	24.9	9.9
Truck, Parts and Other | Parts | Operating Segments
Segment Reporting Information [Line Items]
Net sales and revenues										3,052.9	3,104.7	3,125.9
Truck, Parts and Other | Parts | Intersegment
Segment Reporting Information [Line Items]
Net sales and revenues										(47.2)	(44.6)	(48.4)
Truck, Parts and Other | Other
Segment Reporting Information [Line Items]
Net sales and revenues										73.6	100.2	121.3
Income before income taxes	[1]									(873.3)	(43.2)	(31.9)
Depreciation and amortization										15.8	14.9	11.8
Assets		287.0				211.6				287.0	211.6	106.1
Expenditures for long-lived assets										25.5	17.7	12.1
Financial Services
Segment Reporting Information [Line Items]
Revenue		303.7	$ 296.2	$ 297.4	$ 289.4	292.8	$ 301.0	$ 293.8	$ 284.7	1,186.7	1,172.3	1,204.2
Income before income taxes										306.5	362.6	370.4
Depreciation and amortization										537.2	486.2	485.0
Assets		$ 12,194.8				$ 12,254.6				12,194.8	12,254.6	11,917.3
Expenditures for long-lived assets										$ 1,214.4	$ 1,044.4	$ 935.3

[1] Other includes the $833.0 European Commission charge in 2016.