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Debt - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 1 Months Ended | 3 Months Ended | 6 Months Ended | 3 Months Ended |  | 3 Months Ended |  | 3 Months Ended |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended
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Jun. 01, 2012 | Jun. 30, 2012 | Jun. 30, 2012 | Jun. 30, 2011 | Jun. 30, 2012 First Loan Agreement | Feb. 29, 2012 First Loan Agreement | Jun. 30, 2012 Two Term Loan Agreements | Jan. 31, 2012 Two Term Loan Agreements | Jun. 30, 2012 Revolving Credit Agreement Year | Feb. 29, 2012 Revolving Credit Agreement | Jan. 31, 2012 Revolving Credit Agreement | Jan. 31, 2012 Aluminio Day | Jun. 30, 2012 Aluminio Day | Jun. 30, 2012 Aluminio Day
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayment of outstanding debt | $ 322 |  | $ 659 | $ 1,095 |  |  |  |  |  |  |  |  | $ 215 | $ 275
Outstanding debt, interest rate | 6.00% |  |  |  |  |  |  |  |  |  |  |  |  |
Line Of Credit Facility Amount Outstanding |  |  |  |  | 150 | 100 |  | 350 |  | 100 | 100 | 280 |  |
Pension Contributions |  | $ 139 | $ 352 | $ 103 |  |  |  |  |  |  |  |  |  |
Applicable Margin On LIBOR |  |  |  |  | 1.25% |  | 1.50% |  |  |  |  |  |  |
Line of credit facility, expiration date |  |  |  |  |  |  | Jul. 30, 2012 |  | Dec. 31, 2012 |  |  |  |  |
Revolving credit facility, term |  |  |  |  |  |  |  |  | 5 |  |  |  |  |
Weighted-average interest rate |  |  |  |  |  |  |  |  |  |  |  |  | 2.32% |
Weighted-average maturity days |  |  |  |  |  |  |  |  |  |  |  |  |  |

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- Definition Applicable margin on London Inter Bank Offer Rate loans. + References No definition available. + Details
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- Definition Debt weighted average maturity days. + References No definition available. + Details
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- Definition Interest rate stated in the contractual debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount borrowed under the credit facility as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
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- Definition Date the credit facility terminates, in CCYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
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- Definition The amount of cash or cash equivalents contributed by the entity to fund its pension plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -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. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3536-108585 + Details
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- Definition The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 -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. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3291-108585 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 20 -Subparagraph b -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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