Expense (Income) Reclassified out of AOCI into Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Derivative [Line Items]
Income before income taxes	$ (448.2)	$ 429.6
Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Income before income taxes	50.1	54.8
Truck, Parts and Other
Derivative [Line Items]
Net sales and revenues	(3,935.7)	(4,010.6)
Cost of sales and revenues	3,382.2	3,413.6
Interest and other (income) expense, net	(1.6)	0.1
Income before income taxes	(382.8)	515.6
Financial Services
Derivative [Line Items]
Interest and other expense, net	34.1	30.3
Income before income taxes	(57.3)	(80.3)
Interest-Rate Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Income before income taxes	45.8	57.9
Interest-Rate Contracts | Financial Services | Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Interest and other expense, net	45.8	57.9
Foreign-exchange contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Income before income taxes	4.3	(3.1)
Foreign-exchange contracts | Truck, Parts and Other | Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Net sales and revenues	4.2	(4.8)
Cost of sales and revenues	0.1	0.0
Interest and other (income) expense, net	$ 0.0	$ 1.7