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Contingencies And Commitments - Additional Information (Detail) In Millions, unless otherwise specified | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |  |  | 9 Months Ended | 1 Months Ended |  | 1 Months Ended |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |  | 3 Months Ended | 12 Months Ended |  |  | 3 Months Ended | 9 Months Ended |  |  | 12 Months Ended |  |  | 9 Months Ended |  | 12 Months Ended | 9 Months Ended |  |  | 9 Months Ended |  |  | 12 Months Ended | 3 Months Ended | 9 Months Ended | 18 Months Ended |  | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |  | 3 Months Ended | 9 Months Ended |  |  |  | 1 Months Ended | 9 Months Ended | 1 Months Ended | 12 Months Ended | 0 Months Ended
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Jan. 31, 2007 Day | Nov. 30, 2006 Day | Sep. 30, 2012 USD ($) | Sep. 30, 2011 USD ($) | Sep. 30, 2012 USD ($) mwh MW | Sep. 30, 2012 EUR (€) | Sep. 30, 2011 USD ($) | Dec. 31, 2011 USD ($) | Nov. 08, 2011 Day | Sep. 30, 2012 Non Current Liabilities And Deferred Credits [Member] USD ($) | Dec. 31, 2011 Parent Company [Member] USD ($) | Sep. 30, 2012 Alcoa Aluminio [Member] USD ($) | Sep. 30, 2012 Alcoa Aluminio [Member] BRL | Jul. 31, 2006 Italian Government [Member] Year | Nov. 19, 2009 Italian Government [Member] USD ($) | Nov. 19, 2009 Italian Government [Member] EUR (€) | Jan. 31, 2007 Spanish Government [Member] Year | Jun. 30, 2003 Massena Ny [Member] Year | Sep. 30, 2012 Massena Ny [Member] USD ($) | Nov. 30, 2008 Grasse River [Member] USD ($) | Sep. 30, 2012 Grasse River [Member] USD ($) | Jun. 30, 2012 Grasse River [Member] USD ($) | Sep. 30, 2012 Grasse River [Member] USD ($) | Dec. 31, 2010 Grasse River [Member] USD ($) | Mar. 24, 2010 Grasse River [Member] USD ($) | Sep. 30, 2012 Smelter Sites [Member] USD ($) | Sep. 30, 2012 East St Louis Site [Member] USD ($) | Dec. 31, 2005 East St Louis Site [Member] USD ($) | Dec. 31, 2009 Portovesme Site [Member] USD ($) | Dec. 31, 2010 Smelting And Rolling Mill Companies [Member] USD ($) | Sep. 30, 2012 Smelting And Rolling Mill Companies [Member] Non Current Liabilities And Deferred Credits [Member] USD ($) | Dec. 31, 2011 Smelting And Rolling Mill Companies [Member] Non Current Liabilities And Deferred Credits [Member] USD ($) | Sep. 30, 2012 Alcoa Joint Venture [Member] USD ($) | Sep. 30, 2012 Alcoa Joint Venture [Member] USD ($) Year | Sep. 30, 2012 Alcoa Joint Venture [Member] SAR | Dec. 31, 2011 Alcoa Joint Venture [Member] USD ($) | Dec. 31, 2011 Refining And Mining Company [Member] USD ($) | Sep. 30, 2012 Maaden Joint Venture [Member] | Dec. 31, 2011 Maaden Joint Venture [Member] | Sep. 30, 2012 Alumina Limited [Member] | Jan. 31, 2007 Tariffs Granted By Spain [Member] USD ($) | Jan. 31, 2007 Tariffs Granted By Spain [Member] EUR (€) | Dec. 31, 2009 Fusina Site [Member] USD ($) | Sep. 30, 2012 Machadinho [Member] | Sep. 30, 2012 Barra Grande [Member] | Sep. 30, 2012 Machadinho And Barra Grande [Member] USD ($) | Sep. 30, 2012 Machadinho And Barra Grande [Member] BRL | Dec. 31, 2011 Machadinho And Barra Grande [Member] USD ($) | Dec. 31, 2011 Machadinho And Barra Grande [Member] BRL | Sep. 30, 2012 Serra Do Facao Project [Member] USD ($) | Sep. 30, 2012 Serra Do Facao Project [Member] ZAR | Sep. 30, 2012 Serra Do Facao Project [Member] BRL | Dec. 31, 2011 Serra Do Facao Project [Member] USD ($) | Dec. 31, 2011 Serra Do Facao Project [Member] BRL | Dec. 31, 2007 Serra Do Facao Project [Member] Alcoa Aluminio [Member] | Dec. 31, 2004 Dampier Gas Pipeline [Member] USD ($) | Dec. 31, 2004 Dampier Gas Pipeline [Member] AUD | Sep. 30, 2012 Dampier Gas Pipeline [Member] Three Year Equity Call Plan [Member] USD ($) | Sep. 30, 2012 Dampier Gas Pipeline [Member] Three Year Equity Call Plan [Member] AUD | Sep. 30, 2012 Dampier Gas Pipeline [Member] Three Year Equity Call Plan [Member] USD ($) | Sep. 30, 2012 Dampier Gas Pipeline [Member] Three Year Equity Call Plan [Member] AUD | Sep. 30, 2012 Dampier Gas Pipeline [Member] Three Year Equity Call Plan [Member] USD ($) | Sep. 30, 2012 Dampier Gas Pipeline [Member] Three Year Equity Call Plan [Member] AUD | Sep. 30, 2012 Sherwin, TX [Member] USD ($) | Sep. 30, 2012 Other Sites [Member] USD ($) | Sep. 30, 2012 Other Sites [Member] USD ($) | Sep. 30, 2012 Baie Comeau [Member] USD ($) | Sep. 30, 2012 Mosjoen, Norway [Member] USD ($) | Jun. 30, 2012 Estreito Project [Member] USD ($) | Jun. 30, 2012 Estreito Project [Member] BRL | Sep. 30, 2012 Estreito Project [Member] mwh | Dec. 31, 2011 Estreito Project [Member] USD ($) | Dec. 31, 2011 Estreito Project [Member] ZAR | Dec. 31, 2010 Estreito Project [Member] USD ($) | Dec. 31, 2010 Estreito Project [Member] ZAR | Dec. 31, 2006 Estreito Project [Member] Alcoa Aluminio [Member] | Dec. 31, 2006 Estreito Hydroelectric Power Project [Member] mwh | Sep. 30, 2012 Minimum [Member] USD ($) | Sep. 30, 2012 Maximum [Member] USD ($) | Sep. 30, 2012 Alba [Member] USD ($) | Jun. 30, 2012 Alba [Member] USD ($) | Sep. 30, 2012 Alba [Member] USD ($) | Feb. 27, 2008 Alba [Member] Year | Sep. 30, 2012 Alba [Member] Minimum [Member] USD ($) | Sep. 30, 2012 Alba [Member] Maximum [Member] USD ($) | Sep. 30, 2012 Canada And Norway [Member] Massena Ny [Member] USD ($) | May 31, 2011 Breaches Of Warranty [Member] USD ($) | May 31, 2011 Negligence Award [Member] USD ($) | Sep. 30, 2012 Recurring Costs Of Managing Hazardous Substances And Environmental Programs [Member] | Nov. 30, 2006 Curtis Vs Alcoa [Member] Person | Dec. 31, 2011 Scrg Brownfield Recovery Corp Energy Answers Corporation Of Puerto Rico [Member] USD ($) | Jan. 20, 2011 Scrg Brownfield Recovery Corp Energy Answers Corporation Of Puerto Rico [Member] Breaches Of Warranty [Member] USD ($) | Jan. 20, 2011 Scrg Brownfield Recovery Corp Energy Answers Corporation Of Puerto Rico [Member] Punitive Damages [Member] USD ($) | Jan. 20, 2011 Scrg Brownfield Recovery Corp Energy Answers Corporation Of Puerto Rico [Member] Property Damages [Member] USD ($)
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of alleged conspiracy, years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 15 |  |  |  |  |  |  |  |  |  |  |
Damages claimed, value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of days required to dismiss lawsuit |  |  |  |  |  |  |  |  | 30 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash payment for suit settlement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 45 |  | 40 |  |  |  |  |  |  |  |  |  |  |  |
Restructuring and other charges |  |  | 2 | 9 | 27 |  | 49 | 130 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 45 | 45 |  |  |  |  |  |  |  |  |  |  |  |  |
Restructuring and other charges, after-tax and noncontrolling interests |  |  | 2 | 5 | 19 |  | 26 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 18 | 18 | 15 |  |  |  |  |  |  |  |  |  |  |  |
Alcoa's maximum exposure to loss in projects |  |  | 375 |  | 375 | 303 |  |  |  |  |  | 200 | 400 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90 | 70 |  |  |  | 280 | 560 |  |  |  |  |  |  |  |  |  |  | 520 | 500 | 520 | 500 | 520 | 500 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 75 |  | 75 |  |  |  |  |  |  |  |  |  |  |  |
Contingency settlement agreement amount, total |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 85 |  |  |  |  |  |  |  |  |  |  |  |
Contingency settlement agreement amount paid |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 42.5 |  | 42.5 |  |  |  |  |  |  |  |  |  |  |  |
Contingency settlement agreement amount payable |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 42.5 |  | 42.5 |  |  |  |  |  |  |  |  |  |  |  |
Contingency settlement agreement future payable date |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | October 9, 2013 |  |  |  |  |  |  |  |  |  |  |  |
Percentage of equity interest |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 40.00% |  |  |  |  |  |  |  |  |  |  |  |
Estimated contingency settlement changes, net of tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25 | 30 |  |  |  |  |  |  |  |  |
Retired former employees involved in class action |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 13,000 |  |  |  |
Trial length, number of days |  | 8 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Court granted motion for judgment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 |  |  | 20 | 13 | 6 | 10
Damages awarded to plaintiff, pre-judgment interest |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |
Management estimate for maximum exposure from class action |  |  | 110 |  | 110 | 85 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Provision for contract losses |  |  |  |  |  | 39 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0 | 50 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of years operating under a power supply structure |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 |  |  | 9 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Charge related to European commission announcement |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 250 | 173 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Write-off of receivable |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20 | 14 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Establishment reserve |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 230 | 159 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Recovery amount |  |  |  |  | 375 | 303 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reduction in recovery amount |  |  | 65 |  | 65 | 53 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Italian government |  |  |  |  | 310 | 250 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Italian government, installment amount |  |  |  |  | 62 | 50 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of installments, litigation payment |  |  |  |  | 5 | 5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Litigation reserve |  |  | 204 |  | 204 | 159 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Range of reasonable possible loss, minimum |  |  | 204 |  | 204 | 159 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Days provided to submit observations and comments to the EC | 30 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of cleanup locations |  |  |  |  | More than 100 | More than 100 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remediation reserve balance |  |  | 535 |  | 535 |  |  | 347 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remediation reserve balance, classified as a current liability |  |  | 63 |  | 63 |  |  | 58 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remediation reserve increase |  |  | 174 |  | 204 |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 40 | 128 | 37 | 1 | 2 |  | 30 | 14 | 15 | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  | 12 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 | 10 | 25 | 20 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remediation reserve adjustment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 128 |  |  |  |  |  | 17 | 45 | 14 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 165 |  |  |  |  |  |  |  |
Payments related to remediation expenses applied against the reserve |  |  | 5 |  | 16 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in reserves due to effects of foreign currency translation |  |  | 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of cost of goods sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.00% |  |  |  |  |
Period of time between potential phenomenon occurrences, years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest issued as guarantee for smelting and rolling mill companies |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25.10% | 25.10% |  | 25.10% |  | 74.90% | 74.90% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capital investment |  |  | 1,831 |  | 1,831 |  |  | 1,626 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,035 |  |  | 10,800 | 10,800 | 40,500 |  | 1,992 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount invested by Alcoa and Aluminum Financing Limited |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,100 | 1,100 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Term of investment by Alcoa and Aluminum Financing Limited, years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capital investment commitment paid-to-date |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 611 | 611 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capital investment commitment paid in period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 37 | 202 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity method investment, carrying value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 774 | 774 |  | 565 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantee issued on behalf of smelting and rolling mill companies |  |  |  |  |  |  |  |  |  | 5 | 1,013 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9 | 8 |  |  |  |  | 500 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt service requirements, principal |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 108 |  |  |  |  |  |  | 60 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt service requirements, interest maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50 |  |  |  |  |  |  | 25 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest in joint venture at fair market value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 40.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30.99% | 42.18% |  |  |  |  |  |  |  |  |  |  | 20.00% | 20.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total investment in project |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 252 | 513 | 266 | 496 | 99 |  | 201 | 105 | 196 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional acquired share |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.41% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of total participation in the consortium |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 34.97% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25.49% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Assured energy, megawatts |  |  |  |  | 65 | 65 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 38 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Energy capacity installed, megawatts |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 280 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Assured power from installed capacity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 150 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in estimated cost to complete project |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 130 | 270 |  | 720 | 1,300 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated project costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 500 | 1,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,550 | 5,170 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aluminio's share of project |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 170 | 350 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 650 | 1,320 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commitment expended on the project |  |  |  |  |  |  |  |  |  |  |  | 610 | 1,230 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional contributions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 170 | 350 |  |  |  |  | 141 | 176 | 3 | 2 | 10 | 8 | 15 | 14 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantee expiration year |  |  |  |  | 2027 | 2027 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of power self-sufficiency upon completion of project with full operating capacity |  |  |  |  | 70.00% | 70.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total energy demand |  |  |  |  | 690 | 690 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Initial cash investment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 17 | 24 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Required plan contributions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 40 | 40 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments made under the agreement for future gas transmission services |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 361 | 347 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

X
- Definition Additional acquired shares + References No definition available. + Details
Name: | aa_AdditionalAcquiredShares
Namespace Prefix: | aa_
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