Derivatives And Other Financial Instruments (Schedule Of Derivative Contract Assets And Liabilities That Are Measured And Recognized At Fair Value On A Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value asset derivatives	$ 94		$ 147
Margin held	(22)	[1]	(19)	[1]
Margin posted	(1)	[1]	(41)	[1]
Fair value liability derivatives	737		865
Level 1 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value liability derivatives	64		35
Level 2 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value liability derivatives	44		83
Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value liability derivatives	630		788
Level 1 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value asset derivatives	57		76
Level 2 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value asset derivatives	47		81
Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value asset derivatives	$ 12		$ 9

[1] Margin held represents cash collateral received related to aluminum contracts included in Level 1 and interest rate contracts included in Level 2 and margin posted represents cash collateral paid related to aluminum contracts included in Level 1. At December 31, 2010, margin posted also represents cash collateral paid related to energy contracts included in Level 3. Alcoa elected to net the margin held and posted against the fair value amounts recognized for derivative instruments executed with the same counterparties under master netting arrangements.