Balance Sheet Classification of Gross and Proforma Net Amounts of Derivative Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivative Instruments [Line Items]
Assets, Amount Recognized in Balance Sheet	$ 47.8	$ 48.0
Assets,Amounts Not Offset in Financial Instruments	(11.7)	(16.3)
Assets, Pro Forma Net Amount	36.1	31.7
Liabilities, Amount Recognized in Balance Sheet	52.9	68.6
Liabilities, Amounts Not Offset in Financial Instruments	(11.7)	(16.3)
Liabilities, Pro Forma Net Amount	41.2	52.3
Truck, Parts and Other | Foreign-exchange contracts
Derivative Instruments [Line Items]
Assets, Amount Recognized in Balance Sheet	0.2	0.6
Assets,Amounts Not Offset in Financial Instruments	(0.2)	(0.2)
Assets, Pro Forma Net Amount		0.4
Liabilities, Amount Recognized in Balance Sheet	1.2	0.8
Liabilities, Amounts Not Offset in Financial Instruments	(0.2)	(0.2)
Liabilities, Pro Forma Net Amount	1.0	0.6
Financial Services | Foreign-exchange contracts
Derivative Instruments [Line Items]
Assets, Amount Recognized in Balance Sheet	0.1	1.1
Assets, Pro Forma Net Amount	0.1	1.1
Liabilities, Amount Recognized in Balance Sheet	2.1	0.1
Liabilities, Pro Forma Net Amount	2.1	0.1
Financial Services | Interest Rate Contract
Derivative Instruments [Line Items]
Assets, Amount Recognized in Balance Sheet	47.5	46.3
Assets,Amounts Not Offset in Financial Instruments	(11.5)	(16.1)
Assets, Pro Forma Net Amount	36.0	30.2
Liabilities, Amount Recognized in Balance Sheet	49.6	67.7
Liabilities, Amounts Not Offset in Financial Instruments	(11.5)	(16.1)
Liabilities, Pro Forma Net Amount	$ 38.1	$ 51.6