Balance Sheet Classifications, Fair Value, Gross and Pro-Forma Net Amounts of Derivative Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
ASSETS
Derivative assets	$ 89.2	$ 48.0
Pro-forma net amount	84.4us-gaap_DerivativeAssets	31.7us-gaap_DerivativeAssets
LIABILITIES
Derivative liabilities	48.5	68.6
Pro-forma net amount	43.7us-gaap_DerivativeLiabilities	52.3us-gaap_DerivativeLiabilities
Interest Rate Contract \| Financial Services
ASSETS
Less amounts not offset in financial instruments	(3.9)	(16.1)
LIABILITIES
Less amounts not offset in financial instruments	(3.9)	(16.1)
Foreign-exchange contracts \| Truck, Parts and Other
ASSETS
Less amounts not offset in financial instruments	(0.9)	(0.2)
LIABILITIES
Less amounts not offset in financial instruments	(0.9)	(0.2)
Designated as Hedging Instrument
ASSETS
Derivative assets	83.9	46.3
LIABILITIES
Derivative liabilities	47.6	68.3
Designated as Hedging Instrument \| Interest Rate Contract \| Financial Services \| Deferred Taxes And Other Liabilities
LIABILITIES
Derivative liabilities	45.7	67.7
Designated as Hedging Instrument \| Interest Rate Contract \| Financial Services \| Other Assets
ASSETS
Derivative assets	82.7	46.3
Designated as Hedging Instrument \| Foreign-exchange contracts \| Truck, Parts and Other \| Accounts Payable Accrued Expenses And Other
LIABILITIES
Derivative liabilities	1.9	0.6
Designated as Hedging Instrument \| Foreign-exchange contracts \| Truck, Parts and Other \| Other current assets
ASSETS
Derivative assets	1.2
Not Designated as Hedging Instrument
ASSETS
Derivative assets	5.3	1.7
LIABILITIES
Derivative liabilities	0.9	0.3
Not Designated as Hedging Instrument \| Foreign-exchange contracts \| Financial Services \| Deferred Taxes And Other Liabilities
LIABILITIES
Derivative liabilities		0.1
Not Designated as Hedging Instrument \| Foreign-exchange contracts \| Financial Services \| Other Assets
ASSETS
Derivative assets	3.4	1.1
Not Designated as Hedging Instrument \| Foreign-exchange contracts \| Truck, Parts and Other \| Accounts Payable Accrued Expenses And Other
LIABILITIES
Derivative liabilities	0.9	0.2
Not Designated as Hedging Instrument \| Foreign-exchange contracts \| Truck, Parts and Other \| Other current assets
ASSETS
Derivative assets	$ 1.9	$ 0.6

Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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