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Derivatives and Other Financial Instruments - Additional Information (Detail) In Millions, unless otherwise specified | 1 Months Ended | 12 Months Ended |  |  |  | 12 Months Ended |  |  | 1 Months Ended |  |
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Jul. 31, 2012 Contract Plant | Jan. 31, 2012 | Dec. 31, 2013 USD ($) Contract t | Dec. 31, 2013 CAD Contract t | Dec. 31, 2011 USD ($) | Dec. 31, 2012 USD ($) | Sep. 30, 2012 USD ($) | Aug. 31, 2012 | Dec. 31, 2013 Forward Contracts [Member] USD ($) | Dec. 31, 2013 Forward Contracts [Member] BRL | Dec. 31, 2013 Level 3 [Member] USD ($) | Dec. 31, 2012 Level 3 [Member] USD ($) | Jul. 31, 2012 Power Contracts One [Member] | Jul. 31, 2012 Power Contracts Two [Member] | Jan. 31, 2012 Interest Rate Swap [Member] USD ($) | Dec. 31, 2011 Interest Rate Swap [Member] USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net unrealized loss on derivative contracts |  |  |  |  |  |  |  |  |  |  | $ 76 | $ 88 |  |  |  |
Other derivative contracts estimated term of quoted market prices, in years |  |  | 10 years | 10 years |  |  |  |  |  |  |  |  |  |  |  |
Number of contracts | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Power contracts maturity date |  |  |  |  |  |  |  |  |  |  |  |  | Mar. 31, 2014 | Mar. 31, 2016 |  |
Number of smelters | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative asset amount |  |  | 390 |  |  | 596 | 596 |  |  |  | 355 | 550 |  |  |  |
Power purchase period forecasted by derivative instrument |  |  | Through December 2036 | Through December 2036 |  |  |  |  |  |  |  |  |  |  |  |
Period of natural gas supply contract |  |  | 6 years | 6 years |  |  |  |  |  |  |  |  |  |  |  |
Number of commodities involved for valuation of supply contract |  |  | 2 | 2 |  |  |  |  |  |  |  |  |  |  |  |
Number of contracts ceased to qualify as fair value hedge |  |  | 0 | 0 |  |  |  |  |  |  |  |  |  |  |  |
Amount of aluminum kmt designated as fair value hedges |  |  | 412,000 | 412,000 |  |  |  |  |  |  |  |  |  |  |  |
Derivative designated as fair value hedge start period |  |  | 2014 | 2014 |  |  |  |  |  |  |  |  |  |  |  |
Derivative designated as fair value hedge end period |  |  | 2017 | 2017 |  |  |  |  |  |  |  |  |  |  |  |
Face amount of debt the hedges effectively convert from fixed to floating through 2018 |  |  | 200 |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amount of interest rate swaps |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 315 | 550
Long-term debt, interest rate |  | 6.00% |  |  |  |  |  | 4.75% |  |  |  |  |  |  |  |
Long-term debt, maturity date |  | 2012 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain on termination of interest rate swaps |  |  |  |  | 33 |  |  |  |  |  |  |  |  |  |  |
Interest rate cash flow hedges |  |  | 0 |  | 0 | 0 |  |  |  |  |  |  |  |  |  |
Forward contract to purchase to mitigate the foreign currency risk related to a Canadian/Brazilian-denominated loan due in 2014 |  |  | $ 54 | 58 |  |  |  |  | $ 231 | 543 |  |  |  |  |  |
Maturity date of forward contract |  |  |  |  |  |  |  |  | Mar. 31, 2014 | Mar. 31, 2014 |  |  |  |  |  |

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