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Inventories - Schedule of Inventory Components (Detail) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Inventory [Line Items]    
Finished goods $ 575 $ 537
Work-in-process 933 911
Bauxite and alumina 638 656
Purchased raw materials 557 532
Operating supplies 270 263
Inventories $ 2,973 $ 2,899