Expense (Income) Reclassified out of AOCI into Income (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Derivative [Line Items]
Income before income taxes	$ 646.2	$ 652.2	$ 216.6	$ 1,213.9
Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Income before income taxes	(8.5)	26.1	46.3	(5.8)
Truck, Parts and Other
Derivative [Line Items]
Net sales and revenues	4,115.8	4,786.1	8,126.4	9,334.1
Cost of sales and revenues	(3,489.4)	(4,061.2)	(6,903.0)	(7,971.4)
Interest and other borrowing expenses	(2.5)	(1.3)	(2.6)	(5.8)
Income before income taxes	562.5	556.1	46.9	1,023.7
Financial Services
Derivative [Line Items]
Interest and other expense, net	(32.6)	(29.6)	(62.9)	(58.7)
Income before income taxes	77.3	90.8	157.6	179.8
Interest-Rate Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Income before income taxes	(7.6)	25.4	50.3	(7.8)
Interest-Rate Contracts | Financial Services | Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Interest and other expense, net	(7.6)	25.4	50.3	(7.8)
Foreign-exchange contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Income before income taxes	(0.9)	0.7	(4.0)	2.0
Foreign-exchange contracts | Truck, Parts and Other | Derivative Contracts | Reclassification out of Accumulated Other Comprehensive Income
Derivative [Line Items]
Net sales and revenues	(1.7)	0.3	(6.5)	0.3
Cost of sales and revenues	0.6	0.2	0.6	3.4
Interest and other borrowing expenses	$ 0.2	$ 0.2	$ 1.9	$ (1.7)