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Derivatives and Other Financial Instruments - Schedule of Reconciliation of Activity for Derivative Contracts (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2011
Aluminum Contracts [Member] | Assets [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Balance at beginning of year | $ 10 |
Sales | (8) |
Cost of goods sold | (107) |
Other income, net | 16 |
Other comprehensive loss | 10 | 5
Purchases, sales, issuances, and settlements | 596 | 5
Transfers into and (or) out of Level 3 |  |
Foreign currency translation | 30 |
Balance at end of year | 547 | 10
Sales |  |
Cost of goods sold |  |
Other income, net | 16 |
Aluminum Contracts [Member] | Liabilities [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Balance at beginning of year | 602 | 702
Sales | (33) | (63)
Other comprehensive loss | 39 | (37)
Transfers into and (or) out of Level 3 |  |
Balance at end of year | 608 | 602
Sales |  |
Cost of goods sold |  |
Energy Contracts [Member] | Assets [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Balance at beginning of year | 2 | 9
Other comprehensive loss | 1 | (7)
Transfers into and (or) out of Level 3 |  |
Balance at end of year | 3 | 2
Sales |  |
Cost of goods sold |  |
Energy Contracts [Member] | Liabilities [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Balance at beginning of year |  | 62
Cost of goods sold |  | (14)
Other income, net |  | (48)
Transfers into and (or) out of Level 3 |  |
Sales |  |
Cost of goods sold |  |
Embedded Credit Derivative [Member] | Liabilities [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Balance at beginning of year | 28 | 24
Cost of goods sold | (1) | (1)
Other income, net | 3 | 5
Transfers into and (or) out of Level 3 |  |
Balance at end of year | 30 | 28
Sales |  |
Cost of goods sold |  |
Other income, net | $ 3 | $ 5

X
- Definition Fair value assets measured on recurring basis gain loss included in cost of goods sold. + References No definition available. + Details
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- Definition Fair Value Assets Measured On Recurring Basis Gain Loss Included In Other Expenses + References No definition available. + Details
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- Definition Fair value assets measured on recurring basis gain loss included in sales. + References No definition available. + Details
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- Definition Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Cost Of Goods Sold + References No definition available. + Details
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- Definition Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Foreign Currency Translation Adjustments + References No definition available. + Details
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- Definition Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Other Expenses + References No definition available. + Details
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- Definition Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Sales Increase Decrease + References No definition available. + Details
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- Details
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- Definition Amount of gain (loss) recognized in other comprehensive income, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3). + 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)(1a) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258 + Details
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- Definition Amount of purchases, sales, issues, and settlements (net) which have taken place in relation to assets measured at fair value on a recurring basis using unobservable inputs (level 3). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 157 -Paragraph 32 -Subparagraph c(2) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Definition This element represents [net] transfers in to and out of assets measured at fair value on a recurring basis using unobservable inputs (Level 3) which have taken place during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 157 -Paragraph 32 -Subparagraph c(3) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Definition This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances. + 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=7578670&loc=d3e19207-110258 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 157 -Paragraph 32 -Subparagraph c -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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