Expense (Income) Reclassified out of AOCI into Income (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
Derivative [Line Items]
Income before income taxes									$ (1,130.4)	$ (2,337.1)	$ (2,017.6)
Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Income before income taxes									10.8	(29.3)	(23.5)
Truck, Parts and Other
Derivative [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 borrowing expenses									11.6	12.3	5.5
Income before income taxes									(796.3)	(1,952.7)	(1,624.9)
Financial Services
Derivative [Line Items]
Interest and other expense, net	$ 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)
Interest-Rate Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Income before income taxes									36.8	(28.5)	(21.7)
Interest-Rate Contracts | Truck, Parts and Other | Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [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 borrowing expenses									0.0	0.0	0.0
Interest-Rate Contracts | Financial Services | Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Interest and other expense, net									36.8	(28.5)	(21.7)
Foreign-exchange contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Income before income taxes									(26.0)	(0.8)	(1.8)
Foreign-exchange contracts | Truck, Parts and Other | Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [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 borrowing expenses									1.3	(4.1)	(2.1)
Foreign-exchange contracts | Financial Services | Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Interest and other expense, net									$ 0.0	$ 0.0	$ 0.0