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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
	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net income (loss) attributable to Alcoa common shareholders	$ 195us-gaap_NetIncomeLoss	$ (178)us-gaap_NetIncomeLoss
Less: preferred stock dividends declared	17us-gaap_PreferredStockDividendsAndOtherAdjustments	1us-gaap_PreferredStockDividendsAndOtherAdjustments
Net income (loss) available to Alcoa common shareholders - basic	178us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic	(179)us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
Add: dividends related to mandatory convertible preferred stock	0us-gaap_ConvertiblePreferredDividendsNetOfTax	0us-gaap_ConvertiblePreferredDividendsNetOfTax
Add: interest expense related to convertible notes	0us-gaap_InterestOnConvertibleDebtNetOfTax	0us-gaap_InterestOnConvertibleDebtNetOfTax
Net income (loss) available to Alcoa common shareholders - diluted	$ 178us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted	$ (179)us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted
Average shares outstanding - basic	1,221us-gaap_WeightedAverageNumberOfSharesOutstandingBasic	1,101us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
Stock options	6us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements
Stock and performance awards	11us-gaap_IncrementalCommonSharesAttributableToNonvestedSharesWithForfeitableDividends
Mandatory convertible preferred stock	0aa_IncrementalCommonSharesAttributableToMandatoryConvertiblePreferredStockDividends	0aa_IncrementalCommonSharesAttributableToMandatoryConvertiblePreferredStockDividends
Convertible notes	0us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities	0us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities
Average shares outstanding - diluted	1,238us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding	1,101us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of mandatory convertible preferred stock dividends.

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The after-tax amount of any dividends on convertible preferred stock.

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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.

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Nonvested equity-based payment awards that contain forfeitable rights to dividends or dividend equivalents (whether paid or unpaid) that result in incremental common shares.

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Net Income or Loss Available to Common Stockholders plus adjustments resulting from the assumption that dilutive convertible securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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