Reclassifications Out of Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains and Losses on cash flow hedges, after-tax expense reduction	$ (20.8)
Unrealized gains and losses on marketable debt securities, after-tax income increase	1.0
Defined benefit pension plans, actuarial (loss), pre-tax expense	22.1
Foreign Currency Translation, pre-tax expense reduction	(2.0)
Total reclassifications out of AOCI	0.3
Available-for-sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gains and losses on marketable debt securities, tax expense	(0.4)
Unrealized gains and losses on marketable debt securities, after-tax income increase	1.0
Available-for-sale Securities | Investment Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gains and losses on marketable debt securities, pre-tax expense	1.4
Truck, Parts and Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit pension plans, prior service costs, pre-tax expense	0.9
Defined benefit pension plans, actuarial (loss), pre-tax expense	31.7
Truck, Parts and Other | Cost of sales and revenues
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit pension plans, prior service costs, pre-tax expense	0.8
Defined benefit pension plans, actuarial (loss), pre-tax expense	(17.4)
Truck, Parts and Other | Interest and other expense (income) , net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Foreign Currency Translation, pre-tax expense reduction	(1.1)
Truck, Parts and Other | SG&A
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit pension plans, prior service costs, pre-tax expense	0.1
Defined benefit pension plans, actuarial (loss), pre-tax expense	(14.2)
Truck, Parts and Other | Foreign-exchange contracts | Cost of sales and revenues
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains and Losses on cash flow hedges, pre-tax expense reduction	(0.5)
Truck, Parts and Other | Foreign-exchange contracts | Interest and other expense (income) , net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains and Losses on cash flow hedges, pre-tax expense reduction	(0.2)
Financial Services
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains and Losses on cash flow hedges, pre-tax expense reduction	(29.8)
Gains and Losses on cash flow hedges, tax expense	9.0
Financial Services | Interest and other borrowing expenses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Foreign Currency Translation, pre-tax expense reduction	(0.9)
Financial Services | SG&A
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit pension plans, actuarial (loss), pre-tax expense	1.3
Financial Services | Pre-tax expense increase
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit pension plans, actuarial (loss), pre-tax expense	33.9
Financial Services | Tax benefit
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit pension plans, actuarial (loss), pre-tax expense	(11.8)
Financial Services | After-tax expense increase
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit pension plans, actuarial (loss), pre-tax expense	22.1
Financial Services | Interest Rate Contract | Interest and other borrowing expenses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains and Losses on cash flow hedges, pre-tax expense reduction	$ (29.1)