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Subsequent Events - Additional Information (Detail) (Subsequent Event [Member], USD $) |  | 0 Months Ended |  | 0 Months Ended
--- | --- | --- | --- | ---
Oct. 15, 2014 Alcoa World Alumina and Chemicals [Member] | Oct. 15, 2014 Jamalco Joint Venture [Member] | Oct. 15, 2014 Alcoa [Member] | Oct. 23, 2014 Mt Holly [Member] | Oct. 15, 2014 Minimum [Member] | Oct. 15, 2014 Maximum [Member]
Subsequent Event [Line Items] |  |  |  |  |  |
Percentage of ownership to sell | 100.00% |  |  | 50.33% |  |
Percentage of ownership by a subsidiary of Alcoa World Alumina and Chemicals |  | 55.00% |  |  |  |
Non-cash loss |  |  |  |  | $ 265,000,000 | $ 285,000,000
Non-cash loss after-tax and noncontrolling interest |  |  |  |  | $ 80,000,000 | $ 100,000,000
Non-cash loss per diluted share |  |  |  |  | $ 0.07 | $ 0.09
Percentage of ownership by Alcoa |  |  | 60.00% |  |  |

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