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Derivatives and Other Financial Instruments - Schedule of Reconciliation of Activity for Derivative Contracts (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014
Aluminum Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets, Beginning balance	$ 281	$ 349
Fair value measurement, Assets, Sales
Fair value measurement, Assets, Cost of goods sold	(36)	(147)
Fair value measurement, Assets, Other expenses, net	(12)	(13)
Fair value measurement, Assets, Other comprehensive loss	(11)	(11)
Fair value measurement, Assets, Purchases, sales, issuances, and settlements
Fair value measurement, Assets, Transfers into and/or out of Level 3
Fair value measurement, Assets, Foreign currency translation	(5)	39
Fair value measurement, Assets, Ending balance	217	217
Fair value measurement, Assets, Sales
Fair value measurement, Assets, Cost of goods sold
Fair value measurement, Assets, Other expenses, net	(12)	(13)
Fair value measurement, Liabilities, Beginning balance	422	410
Fair value measurement, Liabilities, Sales	(8)	(19)
Fair value measurement, Liabilities, Cost of goods sold
Fair value measurement, Liabilities, Other income, net
Fair value measurement, Liabilities, Other comprehensive income	(7)	16
Fair value measurement, Liabilities, Purchases, sales, issuances, and settlements
Fair value measurement, Liabilities, Transfers into and/or out of Level 3
Fair value measurement, Liabilities, Foreign currency translation
Fair value measurement, Liabilities, Ending balance	407	407
Fair value measurement, Liabilities, Sales
Fair value measurement, Liabilities, Cost of goods sold
Fair value measurement, Liabilities, Other income, net
Embedded Credit Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities, Beginning balance	14	21
Fair value measurement, Liabilities, Sales
Fair value measurement, Liabilities, Cost of goods sold
Fair value measurement, Liabilities, Other income, net	10	3
Fair value measurement, Liabilities, Other comprehensive income
Fair value measurement, Liabilities, Purchases, sales, issuances, and settlements
Fair value measurement, Liabilities, Transfers into and/or out of Level 3
Fair value measurement, Liabilities, Foreign currency translation
Fair value measurement, Liabilities, Ending balance	24	24
Fair value measurement, Liabilities, Sales
Fair value measurement, Liabilities, Cost of goods sold
Fair value measurement, Liabilities, Other income, net	10	3
Energy Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets, Beginning balance	24	6
Fair value measurement, Assets, Sales
Fair value measurement, Assets, Cost of goods sold
Fair value measurement, Assets, Other expenses, net	(5)
Fair value measurement, Assets, Other comprehensive loss	(18)	(6)
Fair value measurement, Assets, Purchases, sales, issuances, and settlements
Fair value measurement, Assets, Transfers into and/or out of Level 3
Fair value measurement, Assets, Foreign currency translation	(1)
Fair value measurement, Assets, Ending balance
Fair value measurement, Assets, Sales
Fair value measurement, Assets, Cost of goods sold
Fair value measurement, Assets, Other expenses, net	(5)
Fair value measurement, Liabilities, Beginning balance
Fair value measurement, Liabilities, Sales
Fair value measurement, Liabilities, Cost of goods sold
Fair value measurement, Liabilities, Other income, net
Fair value measurement, Liabilities, Other comprehensive income	6	6
Fair value measurement, Liabilities, Purchases, sales, issuances, and settlements
Fair value measurement, Liabilities, Transfers into and/or out of Level 3
Fair value measurement, Liabilities, Foreign currency translation
Fair value measurement, Liabilities, Ending balance	6	6
Fair value measurement, Liabilities, Sales
Fair value measurement, Liabilities, Cost of goods sold
Fair value measurement, Liabilities, Other income, net

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Fair value liabilities measured on recurring basis gain loss included in cost of goods sold.

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Fair value measurement with unobservable inputs reconciliation recurring basis asset foreign currency translation adjustments.

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- Definition

Amount of gain (loss) recognized in other comprehensive income (loss) for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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