Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized (gains) and losses on derivative contracts, pre-tax	$ (29.3)	$ (23.5)	$ (35.6)
Unrealized (gains) and losses on derivative contracts, tax	8.5	5.1	10.8
Unrealized (gains) and losses on derivative contracts, after-tax	(20.8)	(18.4)	(24.8)
Unrealized (gains) and losses on marketable debt securities, pre-tax	(2.1)	(0.9)	1.7
Unrealized (gains) and losses on marketable debt securities, tax	0.6	0.3	(0.5)
Unrealized (gains) and losses on marketable debt securities, after tax	(1.5)	(0.6)	1.2
Pension plans, pre-tax	42.4	22.0	45.3
Pension plans, tax	(14.8)	(7.1)	(15.8)
Pension plans, after tax	27.6	14.9	29.5
Foreign currency translation, after tax			(2.0)
Total reclassifications out of AOCI	5.3	(4.1)	3.9
Truck, Parts and Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension plans, Actuarial loss, pre- tax	39.5	20.1	41.7
Pension plans, Prior service costs, pre-tax	1.2	1.2	1.3
Truck, Parts and Other | Cost of sales and revenues
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension plans, Actuarial loss, pre- tax	22.4	11.1	21.4
Pension plans, Prior service costs, pre-tax	1.0	1.0	0.4
Truck, Parts and Other | Interest and other expense, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Foreign currency translation, after tax			(1.1)
Truck, Parts and Other | Selling, general and administrative
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension plans, Actuarial loss, pre- tax	17.1	9.0	20.3
Pension plans, Prior service costs, pre-tax	0.2	0.2	0.6
Truck, Parts and Other | Research and development
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension plans, Prior service costs, pre-tax			0.3
Truck, Parts and Other | Foreign-exchange contracts | Cost of sales and revenues
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized (gains) and losses on derivative contracts, pre-tax	3.4	0.3	1.0
Truck, Parts and Other | Foreign-exchange contracts | Interest and other expense, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized (gains) and losses on derivative contracts, pre-tax	(4.1)	(2.1)	(0.6)
Truck, Parts and Other | Foreign-exchange contracts | Net sales and revenues
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized (gains) and losses on derivative contracts, pre-tax	(0.1)
Financial Services | Interest and other borrowing expenses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Foreign currency translation, after tax			(0.9)
Financial Services | Selling, general and administrative
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension plans, Actuarial loss, pre- tax	1.7	0.7	2.3
Financial Services | Interest-Rate Contracts | Interest and other borrowing expenses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized (gains) and losses on derivative contracts, pre-tax	$ (28.5)	$ (21.7)	$ (36.0)