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Earnings Per Share - Reconciliation of Information Used to Compute Basic and Diluted EPS (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Earnings Per Share [Abstract] |  |
Net income (loss) attributable to Alcoa common shareholders | $ 195 us-gaap_NetIncomeLoss | $ (178)us-gaap_NetIncomeLoss
Less: preferred stock dividends declared | 17 us-gaap_PreferredStockDividendsAndOtherAdjustments | 1 us-gaap_PreferredStockDividendsAndOtherAdjustments
Net income (loss) available to Alcoa common shareholders - basic | 178 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | (179)us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
Add: dividends related to mandatory convertible preferred stock | 0 us-gaap_ConvertiblePreferredDividendsNetOfTax | 0 us-gaap_ConvertiblePreferredDividendsNetOfTax
Add: interest expense related to convertible notes | 0 us-gaap_InterestOnConvertibleDebtNetOfTax | 0 us-gaap_InterestOnConvertibleDebtNetOfTax
Net income (loss) available to Alcoa common shareholders - diluted | $ 178 us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted | $ (179)us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted
Average shares outstanding - basic | 1,221 us-gaap_WeightedAverageNumberOfSharesOutstandingBasic | 1,101 us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
Stock options | 6 us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements |
Stock and performance awards | 11 us-gaap_IncrementalCommonSharesAttributableToNonvestedSharesWithForfeitableDividends |
Mandatory convertible preferred stock | 0 aa_IncrementalCommonSharesAttributableToMandatoryConvertiblePreferredStockDividends | 0 aa_IncrementalCommonSharesAttributableToMandatoryConvertiblePreferredStockDividends
Convertible notes | 0 us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities | 0 us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities
Average shares outstanding - diluted | 1,238 us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding | 1,101 us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding

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- Definition The after-tax amount of any dividends on convertible preferred stock. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 16 -URI http://asc.fasb.org/extlink&oid=7655603&loc=d3e1505-109256 + Details
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- Definition Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of convertible debt securities using the if-converted method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 40 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=7655603&loc=d3e1930-109256 + Details
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- Definition The aggregate value of preferred stock dividends and other adjustments necessary to derive net income apportioned to common stockholders. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=7655603&loc=d3e1377-109256 + Details
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