Expense (Income) Reclassified out of AOCI into Income (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative [Line Items]
Income before income taxes	$ (581.8)	$ (494.9)	$ (1,569.0)	$ (711.5)
Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Income before income taxes	28.1	16.8	129.6	63.1
Truck, Parts and Other
Derivative [Line Items]
Net sales and revenues	(4,731.5)	(3,953.2)	(13,065.1)	(12,079.6)
Cost of sales and revenues	4,046.8	3,371.5	11,184.2	10,274.5
Interest and other expense, net	3.2	1.6	3.1	4.2
Income before income taxes	(501.6)	(415.4)	(1,351.7)	(462.3)
Financial Services
Derivative [Line Items]
Interest and other borrowing expenses	38.3	32.2	109.8	95.1
Income before income taxes	(71.2)	(71.0)	(191.5)	(228.6)
Interest-Rate Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Income before income taxes	24.6	28.2	110.4	78.5
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	0.0
Cost of sales and revenues	0.0	0.0	0.0	0.0
Interest and other expense, net	0.0	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 borrowing expenses	24.6	28.2	110.4	78.5
Foreign-exchange contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Income before income taxes	3.5	(11.4)	19.2	(15.4)
Foreign-exchange contracts | Truck, Parts and Other | Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Net sales and revenues	(3.0)	(11.1)	13.3	(17.6)
Cost of sales and revenues	5.5	0.0	4.3	0.6
Interest and other expense, net	1.0	(0.3)	1.6	1.6
Foreign-exchange contracts | Financial Services | Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Interest and other borrowing expenses	$ 0.0	$ 0.0	$ 0.0	$ 0.0