Reclassifications Out of Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Schedule of Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains and Losses on cash flow hedges, pre-tax expense reduction	$ (18.1)	[1]
Gains and Losses on cash flow hedges, tax expense	5.3	[1]
Gains and Losses on cash flow hedges, after-tax expense reduction	(12.8)	[1],[2]
Defined benefit pension plans, pre-tax expense	11.2	[1]
Defined benefit pension plans, tax benefit	(3.9)	[1]
Defined benefit pension plans, after-tax expense	7.3	[1],[2]
Total reclassifications out of AOCI	(5.5)	[1],[2]
Truck, Parts and Other
Schedule of Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit pension plans, prior service costs, pre-tax expense	0.3	[1]
Defined benefit pension plans, actuarial (loss), pre-tax expense	10.5	[1]
Truck, Parts and Other | Cost of sales and revenues
Schedule of Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit pension plans, actuarial (loss), pre-tax expense	5.7	[1]
Truck, Parts and Other | SG&A
Schedule of Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit pension plans, actuarial (loss), pre-tax expense	4.8	[1]
Truck, Parts and Other | Foreign-exchange contracts | Cost of sales and revenues
Schedule of Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains and Losses on cash flow hedges, pre-tax expense reduction	(2.3)	[1]
Truck, Parts and Other | Foreign-exchange contracts | Interest and other income (expense), net
Schedule of Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains and Losses on cash flow hedges, pre-tax expense reduction	(0.2)	[1]
Financial Services | SG&A
Schedule of Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit pension plans, actuarial (loss), pre-tax expense	0.4	[1]
Financial Services | Interest Rate Contract | Interest and other borrowing expenses (income)
Schedule of Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains and Losses on cash flow hedges, pre-tax expense reduction	$ (15.6)	[1]

[1] Amounts in parentheses indicate reductions in expenses in the Consolidated Statements of Comprehensive Income. Amounts without parenthesis indicate expenses in the Consolidated Statements of Comprehensive Income.

[2] All amounts are net of tax. Amounts in parentheses indicate reductions in the AOCI component of stockholders' equity.