Derivatives and Other Financial Instruments - Schedule of Fair Values of Outstanding Derivative Contracts Recorded as Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Derivative [Line Items]
Fair value liability derivatives	$ 769	[1]	$ 737	[1]
Level 1 [Member]
Derivative [Line Items]
Fair value liability derivatives	20		64
Level 3 [Member]
Derivative [Line Items]
Fair value liability derivatives	717		630
Level 2 [Member]
Derivative [Line Items]
Fair value liability derivatives	32		44
Derivatives Designated as Hedging Instruments [Member]
Derivative [Line Items]
Fair value liability derivatives	699		653
Derivatives Designated as Hedging Instruments [Member] | Other Current Liabilities [Member] | Aluminum Contracts [Member] | Level 1 [Member]
Derivative [Line Items]
Fair value liability derivatives	17		47
Derivatives Designated as Hedging Instruments [Member] | Other Current Liabilities [Member] | Aluminum Contracts [Member] | Level 3 [Member]
Derivative [Line Items]
Fair value liability derivatives	37		32
Derivatives Designated as Hedging Instruments [Member] | Other Noncurrent Liabilities and Deferred Credits [Member] | Aluminum Contracts [Member] | Level 1 [Member]
Derivative [Line Items]
Fair value liability derivatives			4
Derivatives Designated as Hedging Instruments [Member] | Other Noncurrent Liabilities and Deferred Credits [Member] | Aluminum Contracts [Member] | Level 3 [Member]
Derivative [Line Items]
Fair value liability derivatives	637		570
Derivatives Designated as Hedging Instruments [Member] | Other Noncurrent Liabilities and Deferred Credits [Member] | Energy Contracts [Member] | Level 3 [Member]
Derivative [Line Items]
Fair value liability derivatives	8
Derivatives Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Fair value liability derivatives	70	[2]	85	[2]
Derivatives Not Designated as Hedging Instrument [Member] | Other Current Liabilities [Member] | Aluminum Contracts [Member] | Level 1 [Member]
Derivative [Line Items]
Fair value liability derivatives	3	[2]	12	[2]
Derivatives Not Designated as Hedging Instrument [Member] | Other Current Liabilities [Member] | Aluminum Contracts [Member] | Level 2 [Member]
Derivative [Line Items]
Fair value liability derivatives	21	[2]	23	[2]
Derivatives Not Designated as Hedging Instrument [Member] | Other Current Liabilities [Member] | Embedded Credit Derivative [Member] | Level 3 [Member]
Derivative [Line Items]
Fair value liability derivatives	3	[2]
Derivatives Not Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities and Deferred Credits [Member] | Aluminum Contracts [Member] | Level 1 [Member]
Derivative [Line Items]
Fair value liability derivatives			1	[2]
Derivatives Not Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities and Deferred Credits [Member] | Aluminum Contracts [Member] | Level 2 [Member]
Derivative [Line Items]
Fair value liability derivatives	11	[2]	21	[2]
Derivatives Not Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities and Deferred Credits [Member] | Embedded Credit Derivative [Member] | Level 3 [Member]
Derivative [Line Items]
Fair value liability derivatives	32	[2]	28	[2]
Less Margin Posted [Member] | Other Current Liabilities [Member] | Aluminum Contracts [Member] | Level 1 [Member]
Derivative [Line Items]
Fair value liability derivatives			$ 1	[1]

[1] All margin posted is in the form of cash and is valued under a Level 1 technique. The levels that correspond to the margin posted in the table above reference the level of the corresponding liability for which it is posted. Alcoa elected to net the margin posted against the fair value amounts recognized for derivative instruments executed with the same counterparties under master netting arrangements.

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