Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (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
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes									$ (1,130.4)	$ (2,337.1)	$ (2,017.6)
Tax (benefit) expense									608.7	733.1	658.8
Net Income (Loss)	$ (288.8)	$ (346.2)	$ (481.3)	$ 594.6	$ (347.2)	$ (431.2)	$ (447.2)	$ (378.4)	(521.7)	(1,604.0)	(1,358.8)
Total reclassifications out of AOCI									18.1	5.3	(4.1)
Investment income									(27.6)	(21.8)	(22.3)
Foreign-exchange contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes									(26.0)	(0.8)	(1.8)
Interest-Rate Contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes									36.8	(28.5)	(21.7)
Pension Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications out of AOCI									18.9	27.6	14.9
Pension Plans | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes									28.9	42.4	22.0
Tax (benefit) expense									(10.0)	(14.8)	(7.1)
Net Income (Loss)									18.9	27.6	14.9
Marketable Debt Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications out of AOCI									(2.7)	(1.5)	(0.6)
Marketable Debt Securities | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax (benefit) expense									1.0	0.6	0.3
Net Income (Loss)									(2.7)	(1.5)	(0.6)
Investment income									(3.7)	(2.1)	(0.9)
Derivative Contracts
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications out of AOCI									1.9	(20.8)	(18.4)
Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income taxes									10.8	(29.3)	(23.5)
Tax (benefit) expense									(8.9)	8.5	5.1
Net Income (Loss)									1.9	(20.8)	(18.4)
Truck, Parts and Other
Accumulated Other Comprehensive Income (Loss) [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)
Cost of sales and revenues	3,243.2	3,371.5	3,489.4	3,413.6	3,469.4	3,851.3	4,061.2	3,910.2	13,517.7	15,292.1	15,481.6
Interest and other expense, net									11.6	12.3	5.5
Selling, general and administrative									440.8	445.9	465.2
Income before income taxes									(796.3)	(1,952.7)	(1,624.9)
Truck, Parts and Other | Prior service costs | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of sales and revenues									0.9	1.0	1.0
Selling, general and administrative									0.3	0.2	0.2
Income before income taxes									1.2	1.2	1.2
Truck, Parts and Other | Actuarial loss | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of sales and revenues									13.6	22.4	11.1
Selling, general and administrative									13.0	17.1	9.0
Income before income taxes									26.6	39.5	20.1
Truck, Parts and Other | Derivative Contracts | Foreign-exchange contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net sales and revenues									(27.9)	(0.1)	0.0
Cost of sales and revenues									0.6	3.4	0.3
Interest and other expense, net									1.3	(4.1)	(2.1)
Truck, Parts and Other | Derivative Contracts | Interest-Rate Contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net sales and revenues									0.0	0.0	0.0
Cost of sales and revenues									0.0	0.0	0.0
Interest and other expense, net									0.0	0.0	0.0
Financial Services
Accumulated Other Comprehensive Income (Loss) [Line Items]
Selling, general and administrative									99.4	95.6	96.2
Interest and other borrowing expenses	$ 32.1	$ 32.2	$ 32.6	$ 30.3	$ 30.1	$ 29.2	$ 29.6	$ 29.1	127.2	118.0	133.7
Income before income taxes									(306.5)	(362.6)	(370.4)
Financial Services | Actuarial loss | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Selling, general and administrative									1.1	1.7	0.7
Financial Services | Derivative Contracts | Foreign-exchange contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other borrowing expenses									0.0	0.0	0.0
Financial Services | Derivative Contracts | Interest-Rate Contracts | Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest and other borrowing expenses									$ 36.8	$ (28.5)	$ (21.7)