Expense (Income) Reclassified out of AOCI into Income (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative [Line Items]
Income before income taxes	$ (539.0)	$ (646.2)	$ (987.2)	$ (216.6)
Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Income before income taxes	51.4	(8.5)	101.5	46.3
Truck, Parts and Other
Derivative [Line Items]
Net sales and revenues	(4,397.9)	(4,115.8)	(8,333.6)	(8,126.4)
Cost of sales and revenues	3,755.2	3,489.4	7,137.4	6,903.0
Interest and other expense (income), net	1.5	2.5	(0.1)	2.6
Income before income taxes	(467.3)	(562.5)	(850.1)	(46.9)
Financial Services
Derivative [Line Items]
Interest and other borrowing expenses	37.4	32.6	71.5	62.9
Income before income taxes	(63.0)	(77.3)	(120.3)	(157.6)
Interest-Rate Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Income before income taxes	40.0	(7.6)	85.8	50.3
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 (income), 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	40.0	(7.6)	85.8	50.3
Foreign-exchange contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Income before income taxes	11.4	(0.9)	15.7	(4.0)
Foreign-exchange contracts | Truck, Parts and Other | Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Net sales and revenues	12.1	(1.7)	16.3	(6.5)
Cost of sales and revenues	(1.3)	0.6	(1.2)	0.6
Interest and other expense (income), net	0.6	0.2	0.6	1.9
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