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Derivatives and Other Financial Instruments - Additional Information (Detail) In Millions, unless otherwise specified | 1 Months Ended | 6 Months Ended |  |  |  |  |  | 1 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jul. 31, 2012 Contract Plant | Jan. 31, 2012 | Jun. 30, 2013 USD ($) Kmt Contract | Jun. 30, 2013 CAD Kmt Contract | Jun. 30, 2013 Level 1 [Member] USD ($) | Dec. 31, 2012 Level 1 [Member] USD ($) | Jun. 30, 2013 Level 2 [Member] USD ($) | Dec. 31, 2012 Level 2 [Member] USD ($) | Jun. 30, 2013 Level 3 [Member] USD ($) | Jul. 31, 2012 Power Contracts One [Member] | Jul. 31, 2012 Power Contracts Two [Member] | Jan. 31, 2012 Interest Rate Swap [Member] USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Net unrealized gain on derivative contracts |  |  |  |  |  |  |  |  | $ 2 |  |  |
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 |  |  | 596 |  |  |  |  |  |  |  |  |
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 |  |  | 446 | 446 |  |  |  |  |  |  |  |
Face amount of debt the hedges effectively convert from fixed to floating through 2018 |  |  | 200 |  |  |  |  |  |  |  |  |
Notional amount of interest rate swaps |  |  |  |  |  |  |  |  |  |  |  | 315
Long-term debt, interest rate |  | 6.00% |  |  |  |  |  |  |  |  |  |
Long-term debt, maturity date |  | 2012 |  |  |  |  |  |  |  |  |  |
Interest rate cash flow hedges |  |  | 0 |  |  |  |  |  |  |  |  |
Forward contract to purchase to mitigate the foreign currency risk related to a Canadian-denominated loan due in 2014 |  |  | 56 | 58 |  |  |  |  |  |  |  |
Long-term debt, fair value |  |  |  |  | $ 7,982 | $ 8,936 | $ 521 | $ 569 |  |  |  |

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- Definition Aluminum futures designated as fair value hedges in kilo metric ton. + References No definition available. + Details
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- Definition Interest rate cash flow hedges. + References No definition available. + Details
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- Definition Number of commodities involved for valuation of supply contract. + References No definition available. + Details
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- Definition Number of contracts ceased to qualify as fair value hedge. + References No definition available. + Details
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- Definition Other derivative contracts estimated term of quoted market prices, in years. + References No definition available. + Details
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- Definition Power purchase agreement period forecasted by derivative instrument. + References No definition available. + Details
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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition The amount of foreign currency that the entity has contractually agreed, or for which it has the option, to buy or sell with respect to the contract being described. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13433-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13495-108611 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=20225523&loc=SL20225862-175312 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=28370219&loc=SL20226008-175313 + Details
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- Definition Date the derivative contract matures, in CCYY-MM-DD format. + References No definition available. + Details
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- Definition Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258 + Details
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- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
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