Summary of Significant Accounting Policies - Weighted-Average Useful Lives of Structures and Machinery and Equipment (Detail)	12 Months Ended
	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