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Summary of Significant Accounting Policies - Weighted-Average Useful Lives of Structures and Machinery and Equipment (Detail) | 12 Months Ended
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Dec. 31, 2012
Structures [Member] | Alumina refining [Member] |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 30 years
Structures [Member] | Bauxite mining [Member] |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 33 years
Structures [Member] | Aluminum smelting [Member] |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 35 years
Structures [Member] | Power generation [Member] |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 34 years
Structures [Member] | Global Rolled Products [Member] |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 32 years
Structures [Member] | Engineered Products and Solutions [Member] |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 29 years
Machinery and equipment [Member] | Alumina refining [Member] |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 25 years
Machinery and equipment [Member] | Bauxite mining [Member] |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 19 years
Machinery and equipment [Member] | Aluminum smelting [Member] |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 21 years
Machinery and equipment [Member] | Power generation [Member] |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 24 years
Machinery and equipment [Member] | Global Rolled Products [Member] |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 21 years
Machinery and equipment [Member] | Engineered Products and Solutions [Member] |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 18 years

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- Details
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- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
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