Derivatives And Other Financial Instruments (Fair Value Of Outstanding Derivative Contracts Recorded As Liabilities) (Details) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010
Fair value liability derivatives	$ 737		$ 865
Other Current Liabilities [Member] | Derivatives Designated As Hedging Instruments [Member] | Aluminum Contracts [Member]
Fair value liability derivatives	90		89
Other Current Liabilities [Member] | Derivatives Not Designated As Hedging Instruments [Member] | Aluminum Contracts [Member]
Fair value liability derivatives	43	[1]	52	[1]
Other Current Liabilities [Member] | Derivatives Not Designated As Hedging Instruments [Member] | Energy Contract [Member]
Fair value liability derivatives			62	[1]
Other Current Liabilities [Member] | Aluminum Contracts [Member]
Fair value liability derivatives	8		4
Other Current Liabilities [Member] | Energy Contract [Member]
Fair value liability derivatives			37
Other Noncurrent Liabilities [Member]
Fair value liability derivatives	8		41
Other Noncurrent Liabilities [Member] | Derivatives Designated As Hedging Instruments [Member] | Aluminum Contracts [Member]
Fair value liability derivatives	554		647
Other Noncurrent Liabilities [Member] | Derivatives Not Designated As Hedging Instruments [Member] | Aluminum Contracts [Member]
Fair value liability derivatives	24	[1]	33	[1]
Other Noncurrent Liabilities [Member] | Derivatives Not Designated As Hedging Instruments [Member] | Embedded Credit Derivative [Member]
Fair value liability derivatives	33	[1]	23	[1]
Other Noncurrent Liabilities [Member] | Derivatives Not Designated As Hedging Instruments [Member] | Foreign Exchange Contracts [Member]
Fair value liability derivatives	1	[1]
Derivatives Designated As Hedging Instruments [Member]
Fair value liability derivatives	644		736
Derivatives Not Designated As Hedging Instruments [Member]
Fair value liability derivatives	$ 101	[1]	$ 170	[1]

[1] See the "Other" section within Note P for additional information on Alcoa's purpose for entering into derivatives not designated as hedging instruments and its overall risk management strategies.