Balance Sheet Classifications and Fair Value of Derivative Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
ASSETS
Derivative assets	$ 47.8	$ 48.0
LIABILITIES
Derivative liabilities	52.9	68.6
Interest Rate Contract | Financial Services
ASSETS
Derivative assets	47.5	46.3
LIABILITIES
Derivative liabilities	49.6	67.7
Foreign-exchange contracts | Financial Services
ASSETS
Derivative assets	0.1	1.1
LIABILITIES
Derivative liabilities	2.1	0.1
Foreign-exchange contracts | Truck, Parts and Other
ASSETS
Derivative assets	0.2	0.6
LIABILITIES
Derivative liabilities	1.2	0.8
Designated as Hedging Instrument
ASSETS
Derivative assets	47.6	46.3
LIABILITIES
Derivative liabilities	50.2	68.3
Designated as Hedging Instrument | Interest Rate Contract | Financial Services | Other Assets
ASSETS
Derivative assets	47.5	46.3
Designated as Hedging Instrument | Interest Rate Contract | Financial Services | Deferred Taxes And Other Liabilities
LIABILITIES
Derivative liabilities	49.6	67.7
Designated as Hedging Instrument | Foreign-exchange contracts | Truck, Parts and Other | Other current assets
ASSETS
Derivative assets	0.1
Designated as Hedging Instrument | Foreign-exchange contracts | Truck, Parts and Other | Accounts Payable Accrued Expenses And Other Current Liabilities
LIABILITIES
Derivative liabilities	0.6	0.6
Not Designated as Hedging Instrument
ASSETS
Derivative assets	0.2	1.7
LIABILITIES
Derivative liabilities	2.7	0.3
Not Designated as Hedging Instrument | Foreign-exchange contracts | Financial Services | Other Assets
ASSETS
Derivative assets	0.1	1.1
Not Designated as Hedging Instrument | Foreign-exchange contracts | Financial Services | Deferred Taxes And Other Liabilities
LIABILITIES
Derivative liabilities	2.1	0.1
Not Designated as Hedging Instrument | Foreign-exchange contracts | Truck, Parts and Other | Other current assets
ASSETS
Derivative assets	0.1	0.6
Not Designated as Hedging Instrument | Foreign-exchange contracts | Truck, Parts and Other | Accounts Payable Accrued Expenses And Other Current Liabilities
LIABILITIES
Derivative liabilities	$ 0.6	$ 0.2