Balance Sheet Classification of Gross and Proforma Net Amounts of Derivative Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments [Line Items]
Assets, Amount Recognized in Balance Sheet	$ 48.0	$ 5.1
Assets,Amounts Not Offset in Financial Instruments	(16.3)	(2.6)
Assets, Pro Forma Net Amount	31.7	2.5
Liabilities, Amount Recognized in Balance Sheet	68.6	113.0
Liabilities, Amounts Not Offset in Financial Instruments	(16.3)	(2.6)
Liabilities, Pro Forma Net Amount	52.3	110.4
Foreign-exchange contracts
Derivative Instruments [Line Items]
Liabilities, Amount Recognized in Balance Sheet	0.1
Liabilities, Pro Forma Net Amount	0.1
Truck, Parts and Other | Foreign-exchange contracts
Derivative Instruments [Line Items]
Assets, Amount Recognized in Balance Sheet	0.6	0.5
Assets,Amounts Not Offset in Financial Instruments	(0.2)
Assets, Pro Forma Net Amount	0.4	0.5
Liabilities, Amount Recognized in Balance Sheet	0.8	0.3
Liabilities, Amounts Not Offset in Financial Instruments	(0.2)
Liabilities, Pro Forma Net Amount	0.6	0.3
Financial Services | Foreign-exchange contracts
Derivative Instruments [Line Items]
Assets, Amount Recognized in Balance Sheet	1.1
Assets, Pro Forma Net Amount	1.1
Liabilities, Amount Recognized in Balance Sheet		0.4
Liabilities, Pro Forma Net Amount		0.4
Financial Services | Interest Rate Contract
Derivative Instruments [Line Items]
Assets, Amount Recognized in Balance Sheet	46.3	4.6
Assets,Amounts Not Offset in Financial Instruments	(16.1)	(2.6)
Assets, Pro Forma Net Amount	30.2	2.0
Liabilities, Amount Recognized in Balance Sheet	67.7	112.3
Liabilities, Amounts Not Offset in Financial Instruments	(16.1)	(2.6)
Liabilities, Pro Forma Net Amount	$ 51.6	$ 109.7