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Inventories - Schedule of Inventory Components (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Inventory Disclosure [Abstract]    
Finished goods $ 768us-gaap_InventoryFinishedGoodsNetOfReserves $ 578us-gaap_InventoryFinishedGoodsNetOfReserves
Work-in-process 1,035us-gaap_InventoryWorkInProcessNetOfReserves 828us-gaap_InventoryWorkInProcessNetOfReserves
Bauxite and alumina 578us-gaap_OtherInventoryNetOfReserves 581us-gaap_OtherInventoryNetOfReserves
Purchased raw materials 508us-gaap_InventoryRawMaterialsNetOfReserves 474us-gaap_InventoryRawMaterialsNetOfReserves
Operating supplies 193us-gaap_InventorySuppliesNetOfReserves 244us-gaap_InventorySuppliesNetOfReserves
Inventories, total $ 3,082us-gaap_InventoryNet $ 2,705us-gaap_InventoryNet