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Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2012
Weighted-Average Useful Lives of Structures and Machinery and Equipment | The following table details the weighted-average useful lives of structures and machinery and equipment by reporting segment (numbers in years):
Segment |  | Structures |  |  | Machinery and equipment |
Alumina: |  |  |  |  |  |  |  |
Alumina refining |  |  | 30 |  |  |  | 25 |
Bauxite mining |  |  | 33 |  |  |  | 19 |
Primary Metals: |  |  |  |  |  |  |  |
Aluminum smelting |  |  | 35 |  |  |  | 21 |
Power generation |  |  | 34 |  |  |  | 24 |
Global Rolled Products |  |  | 32 |  |  |  | 21 |
Engineered Products and Solutions |  |  | 29 |  |  |  | 18 |
Weighted-Average Useful Lives of Software and Other Intangible Assets | The following table details the weighted-average useful lives of software and other intangible assets by reporting segment (numbers in years):
Segment |  | Software |  |  | Other intangible assets |
Alumina |  |  | 10 |  |  |  | - |
Primary Metals |  |  | 9 |  |  |  | 36 |
Global Rolled Products |  |  | 10 |  |  |  | 13 |
Engineered Products and Solutions |  |  | 9 |  |  |  | 19 |

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