Reclassifications Out of Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains and Losses on derivative contracts, pre-tax expense reduction	$ (35.6)	$ 22.7	$ 47.7
Gains and Losses on derivative contracts, tax expense	10.8	(7.8)	(17.7)
Gains and Losses on derivative contracts, after-tax expense reduction	(24.8)
Unrealized gains and losses on marketable debt securities, pre-tax expense	1.7	(2.9)	1.6
Unrealized gains and losses on marketable debt securities, tax expense	(0.5)	0.8	(0.6)
Unrealized gains and losses on marketable debt securities, after-tax income increase	1.2
Pension plans, pre-tax expense	45.3	45.4	26.2
Pension plans, tax expense	(15.8)	(15.2)	(9.0)
Pension plans, net of tax	29.5
Foreign Currency Translation, after-tax expense reduction	(2.0)
Total reclassifications out of AOCI	3.9
Available-for-sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gains and losses on marketable debt securities, pre-tax expense	1.7
Unrealized gains and losses on marketable debt securities, tax expense	(0.5)
Unrealized gains and losses on marketable debt securities, after-tax income increase	1.2
Truck, Parts and Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension plans, prior service costs, pre-tax expense	1.3
Pension plans, actuarial (loss), pre-tax expense	41.7
Truck, Parts and Other | Cost of sales and revenues
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension plans, prior service costs, pre-tax expense	0.4
Pension plans, actuarial (loss), pre-tax expense	(21.4)
Truck, Parts and Other | Interest and other expense (income) , net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Foreign Currency Translation, after-tax expense reduction	(1.1)
Truck, Parts and Other | SG&A
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension plans, prior service costs, pre-tax expense	0.6
Pension plans, actuarial (loss), pre-tax expense	(20.3)
Truck, Parts and Other | Foreign-exchange contracts | Cost of sales and revenues
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains and Losses on derivative contracts, pre-tax expense reduction	1.0
Truck, Parts and Other | Foreign-exchange contracts | Interest and other expense (income) , net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains and Losses on derivative contracts, pre-tax expense reduction	(0.6)
Financial Services
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains and Losses on derivative contracts, pre-tax expense reduction	(35.6)
Gains and Losses on derivative contracts, tax expense	10.8
Financial Services | Interest and other borrowing expenses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Foreign Currency Translation, after-tax expense reduction	(0.9)
Financial Services | SG&A
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension plans, actuarial (loss), pre-tax expense	2.3
Financial Services | Pre-tax expense increase
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension plans, pre-tax expense	45.3
Financial Services | Tax benefit
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension plans, tax expense	(15.8)
Financial Services | After-tax expense increase
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension plans, net of tax	29.5
Financial Services | Interest Rate Contract | Interest and other borrowing expenses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains and Losses on derivative contracts, pre-tax expense reduction	$ (36.0)