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Contingencies and Commitments - Additional Information - 1 (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2015 | Jun. 30, 2015 | Sep. 30, 2015 | Dec. 31, 2014 | Dec. 31, 2012 | Dec. 31, 2009
Loss Contingencies [Line Items] |  |  |  |  |  |
Number of cleanup locations |  |  | More than 100 |  |  |
Remediation reserve balance | $ 558 |  | $ 558 | $ 543 |  |
Remediation reserve balance, classified as a current liability | 63 |  | 63 | 70 |  |
Increase in remediation reserve | 1 |  |  |  |  |
Payments related to remediation expenses applied against the reserve | 14 |  | 30 |  |  |
Increase (Decrease) in reserves due to effects of foreign currency translation | 10 |  | $ 16 |  |  |
Actual remediation fieldwork period |  |  | 4 years |  |  |
Guarantee debt service expiration year |  |  | 2019 |  |  |
Firth Rixson [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Increase (Decrease) in reserves due to acquisition | 5 |  | $ 5 |  |  |
Minimum [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Majority of the project funding period |  |  | 2016 |  |  |
Maximum [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Planning and design phase period |  |  | 3 years |  |  |
Majority of the project funding period |  |  | 2020 |  |  |
Recurring Costs of Managing Hazardous Substances and Environmental Programs [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Percentage of cost of goods sold |  |  | 2.00% |  |  |
Grasse River [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Increase in remediation reserve | 3 |  | $ 56 |  |  |
Mosjoen [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Increase in remediation reserve | 1 | $ 11 | 12 |  | $ 20 |
Other Sites [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Remediation reserve adjustment | 2 |  | 8 |  |  |
Pocos De Caldas Smelter and the Anglesea Power Station [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Remediation reserve adjustment | 29 |  |  |  |  |
Portovesme [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Increase in remediation reserve |  |  |  | 3 |  | $ 3
Remediation reserve adjustment |  |  | 7 |  |  |
Massena West, NY [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Remediation reserve balance | 235 |  | 235 | 239 |  |
Sherwin, TX site [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Remediation reserve balance | 31 |  | 31 | 32 |  |
Expected portion of funding through 2019 | 16 |  | 16 |  |  |
East St. Louis, IL Site [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Remediation reserve balance | $ 11 |  | $ 11 | $ 15 |  |

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