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Summary Of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2011
Summary Of Significant Accounting Policies [Abstract] |
Weighted-Average Useful Lives Of Structures And Machinery And Equipment |
Segment |  | Structures |  |  | Machinery and equipment |
Alumina |  |  | 29 |  |  |  | 25 |
Primary Metals |  |  | 34 |  |  |  | 21 |
Flat-Rolled Products |  |  | 31 |  |  |  | 21 |
Engineered Products and Solutions |  |  | 27 |  |  |  | 18 |
Weighted-Average Useful Lives Of Software And Other Intangible Assets |
Segment |  | Software |  |  | Other intangible assets |
Alumina |  |  | 10 |  |  |  | - |
Primary Metals |  |  | 10 |  |  |  | 40 |
Flat-Rolled Products |  |  | 9 |  |  |  | 10 |
Engineered Products and Solutions |  |  | 9 |  |  |  | 17 |

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