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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 1 Months Ended | 12 Months Ended |  |  |
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Dec. 31, 2012 | Jul. 31, 2012 | Sep. 30, 2011 | Jan. 31, 2011 | Jan. 31, 2010 | Dec. 31, 2012 Reporting_Unit Y | Dec. 31, 2011 | Dec. 31, 2010 | Mar. 31, 2010
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |
Percent of equity investments in other entity, maximum | 50.00% |  |  |  |  | 50.00% |  |  |
Original maturity of cash equivalents |  |  |  |  |  | 3 months |  |  |
Number of reporting units being subjected to goodwill impairment test |  |  |  |  |  | 9 |  |  |
Minimum number of reporting units being subjected for goodwill impairment test |  |  |  |  |  | 3 |  |  |
Percentage of total goodwill allocated to reporting units |  |  |  |  |  | 90.00% |  |  |
Goodwill | $ 5,170 |  |  |  |  | $ 5,170 | $ 5,157 | $ 5,028 |
Minimum percentage of estimated fair value of reporting unit to be less than carrying amount of goodwill |  |  | 50.00% |  |  |  |  |  |
Market capitalization of common stock | 9,263 |  |  |  |  |  |  |  |
Maximum hedging contracts period, in years |  |  |  |  |  | 5 |  |  |
Change in functional currency of certain Brazilian operations |  |  |  |  | 309 |  |  |  |
Businesses expected to be disposed within, years |  |  |  |  |  | 1 |  |  |
Goodwill impairment threshold, maximum |  | 50.00% | 50.00% | 50.00% |  |  |  |  |
Effect of change in accounting principle presented on financial statement, before tax |  |  |  |  |  |  |  |  | 250
Alcoa World Alumina and Chemicals [Member] |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |
Percent of equity investments in other entity, maximum |  |  |  |  | 60.00% |  |  |  |
Alcoa Fastening Systems [Member] |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |
Goodwill | 1,160 |  |  |  |  | 1,160 |  |  |
Alcoa Power and Propulsion [Member] |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |
Goodwill | 1,628 |  |  |  |  | 1,628 |  |  |
Primary Metals [Member] |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |
Goodwill | 997 |  |  |  |  | 997 |  |  |
Estimated fair value exceeded percentage on carrying value |  |  |  |  |  | 9.20% |  |  |
Engineered Products and Solutions [Member] |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |
Number of reporting units |  |  |  |  |  | 5 |  |  |
Minimum [Member] | Bauxite mining [Member] |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |
Period of mining |  |  |  |  |  | 1 year |  |  |
Maximum [Member] | Bauxite mining [Member] |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |
Period of mining |  |  |  |  |  | 5 years |  |  |
Alumina [Member] |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |
Goodwill | 10 |  |  |  |  | 10 | 11 | 12 |
Estimated fair value exceeded percentage on carrying value |  |  |  |  |  | 7.40% |  |  |
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 |  |  |
Global Rolled Products [Member] |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |
Goodwill | $ 214 |  |  |  |  | $ 214 | $ 208 | $ 207 |
Estimated fair value exceeded percentage on carrying value |  |  |  |  |  | 150.00% |  |  |

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