Acquisitions and Divestitures - Summary of Preliminary Allocation of Purchase Price by Major Asset Acquired and Liability Assumed, Amount of Goodwill Recognized and Net Present Value of Potential Earn-out (Detail) (USD $)
In Millions, unless otherwise specified

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Assets:

Goodwill

$ 5,247us-gaap_Goodwill

$ 3,415us-gaap_Goodwill

$ 5,170us-gaap_Goodwill

Total assets

3,470us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets

Liabilities:

Total liabilities

475us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities

Firth Rixson [Member]

Assets:

Receivables from customers

197us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables
/ us-gaap_BusinessAcquisitionAxis
= aa_FirthRixsonMember

Inventories

269us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory
/ us-gaap_BusinessAcquisitionAxis
= aa_FirthRixsonMember

Prepaid expenses and other current assets

28us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets
/ us-gaap_BusinessAcquisitionAxis
= aa_FirthRixsonMember

Properties, plants, and equipment

680us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment
/ us-gaap_BusinessAcquisitionAxis
= aa_FirthRixsonMember

Goodwill

1,898us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= aa_FirthRixsonMember

Other noncurrent assets

398us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets
/ us-gaap_BusinessAcquisitionAxis
= aa_FirthRixsonMember

Total assets

3,470us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets
/ us-gaap_BusinessAcquisitionAxis
= aa_FirthRixsonMember

Liabilities:

Accounts payable

162us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable
/ us-gaap_BusinessAcquisitionAxis
= aa_FirthRixsonMember

Other current liabilities

77us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther
/ us-gaap_BusinessAcquisitionAxis
= aa_FirthRixsonMember

Contingent consideration

130us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedContingentLiability
/ us-gaap_BusinessAcquisitionAxis
= aa_FirthRixsonMember

Other noncurrent liabilities

106us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther
/ us-gaap_BusinessAcquisitionAxis
= aa_FirthRixsonMember

Total liabilities

$ 475us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities
/ us-gaap_BusinessAcquisitionAxis
= aa_FirthRixsonMember

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Amount of assets acquired at the acquisition date.

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The amount of liability arising from an inherited contingency (as defined) which has been recognized as of the acquisition date.

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Amount of asset related to consideration paid in advance for costs that provide economic benefits in future periods, and amount of other assets that are expected to be realized or consumed within one year or the normal operating cycle, if longer, acquired at the acquisition date.

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Amount due from customers or clients for goods or services, including trade receivables, that have been delivered or sold in the normal course of business, and amounts due from others, including related parties expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer, acquired at the acquisition date.

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Amount of liabilities incurred for goods and services received that are used in an entity's business and related party payables, assumed at the acquisition date.

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The amount of inventory recognized as of the acquisition date.

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Amount of liabilities assumed at the acquisition date.

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Amount of other liabilities due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

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Amount of other assets expected to be realized or consumed after one year or the normal operating cycle, if longer, acquired at the acquisition date.

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The amount of property, plant, and equipment recognized as of the acquisition date.

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- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

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-Publisher FASB

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