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Summary Of Significant Accounting Policies (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified | 1 Months Ended | 12 Months Ended
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Dec. 31, 2011 | Sep. 30, 2011 | Jan. 31, 2011 | Jan. 31, 2010 | Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Percent of equity investments in other entity, maximum | 50.00% |  |  |  | 50.00% |  |
Goodwill | $ 5,251 |  |  |  | $ 5,251 | $ 5,122 | $ 5,054
Minimum percentage of estimated fair value of reporting unit to be less than carrying amount of goodwill |  |  |  |  | 50.00% |  |
Market capitalization of common stock | 9,207 |  |  |  |  |  |
Market price of common stock |  |  |  |  | $ 8.65 | $ 15.39 |
Percentage of decline in market price of common stock |  |  |  |  | 44.00% |  |
Maximum hedging contracts period, in years |  |  |  |  | 5 |  |
Minimum number of reporting units being subjected for goodwill impairment test |  |  |  |  | 3 |  |
Number of reporting units being subjected to goodwill impairment test |  |  |  |  | 9 |  |
Number of reporting units, estimated fair value of reporting units less than carrying values |  |  |  |  | 6 |  |
Businesses expected to be disposed within, years |  |  |  |  | 1 |  |
Percentage of total goodwill allocated to reporting units |  |  |  |  | 90.00% |  |
Effect of change in accounting principle presented on financial statement, before tax |  |  |  | 250 |  |  |
Change in functional currency of certain Brazilian operations |  |  |  | 309 |  |  |
Goodwill impairment threshold, maximum |  | 50.00% | 50.00% |  |  |  |
Restructuring and other charges |  |  |  |  | 281 | 207 | 237
Restructuring and other charges, after-tax and noncontrolling interests |  |  |  |  | 181 | 130 | 151
Alcoa Fastening Systems [Member] |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Goodwill | 1,153 |  |  |  | 1,153 |  |
Alcoa Power And Propulsion [Member] |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Goodwill | 1,627 |  |  |  | 1,627 |  |
Alcoa World Alumina And Chemicals [Member] |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Percent of equity investments in other entity, maximum |  |  |  | 60.00% |  |  |
Primary Metals [Member] |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Goodwill | 1,841 |  |  |  | 1,841 |  |
Engineered Products And Solutions [Member] |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Number of reporting units |  |  |  |  | 5 |  |
Engineered Products And Solutions [Member] |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Goodwill | 2,666 |  |  |  | 2,666 | 2,523 | 2,504
Restructuring and other charges |  |  |  |  | (3) | 18 | 64
Alumina [Member] |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Goodwill | 11 |  |  |  | 11 | 12 | 17
Restructuring and other charges |  |  |  |  | 39 | 12 | 5
Alumina [Member] | Alcoa World Alumina And Chemicals [Member] |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Percent of equity investments in other entity, maximum |  |  |  |  |  | 40.00% |
Alumina [Member] | Primary Metals [Member] |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Number of reporting units |  |  |  |  | 4 |  |
Write-Off Of Capitalized Business Acquisition Costs [Member] |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Restructuring and other charges |  |  |  |  |  |  | 18
Restructuring and other charges, after-tax and noncontrolling interests |  |  |  |  |  |  | $ 12

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