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Cash Flow Information - Schedule of Cash Paid for Acquisitions Including Non-Controlling Interest (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Business Combinations [Abstract]
Assets acquired	$ 3,470us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets
Liabilities assumed	475us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities
Contingent consideration liability	(130)us-gaap_BusinessCombinationContingentConsiderationLiability
Equity issued	(610)us-gaap_BusinessAcquisitionEquityInterestIssuedOrIssuableValueAssigned
Noncontrolling interest acquired	31aa_BusinessCombinationsNoncontrollingInterest
Increase in Alcoa's shareholders' equity	(3)aa_ValueAddedInShareholdersEquityDueToAcquisitionOne
Cash paid	2,458us-gaap_PaymentsToAcquireBusinessesGross	0us-gaap_PaymentsToAcquireBusinessesGross	0us-gaap_PaymentsToAcquireBusinessesGross
Less: cash acquired	45us-gaap_CashAcquiredFromAcquisition
Net cash paid	$ 2,413aa_PaymentsForAcquisitionsNetOfCashAcquired	$ 0aa_PaymentsForAcquisitionsNetOfCashAcquired	$ 0aa_PaymentsForAcquisitionsNetOfCashAcquired

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- Definition

Business Combinations Noncontrolling Interest

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- Definition

Payments for acquisitions net of cash acquired

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Value Added In Shareholders Equity Due To Acquisition One

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- Definition

Value of equity interests (such as common shares, preferred shares, or partnership interest) issued or issuable to acquire the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (b)(4)

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Amount of liability recognized arising from contingent consideration in a business combination.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 25

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Amount of assets acquired at the acquisition date.

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Amount of liabilities assumed at the acquisition date.

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- Definition

The cash inflow associated with the acquisition of business during the period (for example, cash that was held by the acquired business).

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133



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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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