XML 51 R40.htm IDEA: XBRL DOCUMENT
v3.21.2

Divestitures - Additional Information (Detail) $ in Millions | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Jun. 30, 2021 USD ($) | Jun. 30, 2021 USD ($) | Mar. 31, 2021 USD ($) Employee t | Jun. 30, 2021 USD ($) | Jun. 30, 2020 USD ($) | Dec. 31, 2020 USD ($) | Mar. 31, 2020 USD ($)
Business Disposition [Line Items] |  |  |  |  |  |  |
Net gain from asset sales |  |  |  | $ 124 | $ 176 |  |
Eastalco Aluminum Smelter Site [Member] | Maryland [Member] |  |  |  |  |  |  |
Business Disposition [Line Items] |  |  |  |  |  |  |
Total consideration | $ 100 | $ 100 |  | 100 |  |  |
Net gain from asset sales | 90 |  |  |  |  |  |
Net cash received | 94 |  |  |  |  |  |
Net gain from asset sales after tax | 89 |  |  |  |  |  |
Warrick Rolling Mill [Member] | Held for Sale [Member] |  |  |  |  |  |  |
Business Disposition [Line Items] |  |  |  |  |  |  |
Total consideration |  |  | $ 670 |  |  |  |
Net gain from asset sales |  | 3 | 27 |  |  |  |
Assets held for sale |  |  |  |  |  | $ 648 |
Liabilities held for sale |  |  |  |  |  | 242 |
Assumption of other postretirement benefit liabilities | $ 66 | 66 |  | $ 66 |  |  |
Decrease in other postretirement benefit liabilities after post closing adjustment |  | 6 |  |  |  |  |
Transaction Costs |  | $ 7 |  |  |  |  |
Estimated liabilities recorded |  |  | $ 70 |  |  |  |
Number of employees | Employee |  |  | 1,150 |  |  |  |
Production of aluminum smelter and power plants (metric ton per year) | t |  |  | 269,000 |  |  |  |
Number of employees | Employee |  |  | 670 |  |  |  |
Elemental Environmental Solutions LLC [Member] |  |  |  |  |  |  |
Business Disposition [Line Items] |  |  |  |  |  |  |
Total consideration |  |  |  |  |  |  | $ 250
Net gain from asset sales |  |  |  |  |  | 181 |
Net cash received |  |  |  |  |  | 200 |
Escrow to be received for divestitures |  |  |  |  |  | $ 50 |

X
- Definition Aluminum smelter and power plant production per annum + References No definition available. + Details
Name: | aa_AluminumSmelterAndPowerPlantProductionPerAnnum
Namespace Prefix: | aa_
Data Type: | num:massItemType
Balance Type: | na
Period Type: | duration

X
- Definition Business disposition. + References No definition available. + Details
Name: | aa_BusinessDispositionLineItems
Namespace Prefix: | aa_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Disposal group including discontinued operation other postretirement benefit liabilities assumed. + References No definition available. + Details
Name: | aa_DisposalGroupIncludingDiscontinuedOperationOtherPostretirementBenefitLiabilitiesAssumed
Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Divesture transaction costs. + References No definition available. + Details
Name: | aa_DivestureTransactionCosts
Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Escrow to be received for divestitures. + References No definition available. + Details
Name: | aa_EscrowToBeReceivedForDivestitures
Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Gain loss on disposition of assets after tax. + References No definition available. + Details
Name: | aa_GainLossOnDispositionOfAssetsAfterTax
Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Increase (decrease) in disposal group including discontinued operation other postretirement benefit liabilities. + References No definition available. + Details
Name: | aa_IncreaseDecreaseInDisposalGroupIncludingDiscontinuedOperationOtherPostretirementBenefitLiabilities
Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Liabilities recorded from disposal group including discontinued operation. + References No definition available. + Details
Name: | aa_LiabilitiesRecordedFromDisposalGroupIncludingDiscontinuedOperation
Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Number of employees. + References No definition available. + Details
Name: | aa_NumberOfEmployees
Namespace Prefix: | aa_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of persons employed by the Entity + References No definition available. + Details
Name: | dei_EntityNumberOfEmployees
Namespace Prefix: | dei_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount classified as assets attributable to disposal group held for sale or disposed of. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=109222160&loc=d3e1107-107759 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2941-110230 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 5B -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=109222650&loc=SL51721673-107760 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=109222160&loc=SL51721533-107759 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=109222650&loc=SL51721683-107760 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 5C -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=109222650&loc=SL51721675-107760 + Details
Name: | us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation. + References No definition available. + Details
Name: | us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of gain (loss) on sale or disposal of assets, including but not limited to property plant and equipment, intangible assets and equity in securities of subsidiaries or equity method investee. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585 + Details
Name: | us-gaap_GainLossOnDispositionOfAssets1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount classified as liabilities attributable to disposal group held for sale or disposed of. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=109222650&loc=SL51721683-107760 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=109222160&loc=d3e1107-107759 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 5C -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=109222650&loc=SL51721675-107760 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2941-110230 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=109222160&loc=SL51721533-107759 Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 5B -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=109222650&loc=SL51721673-107760 + Details
Name: | us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The cash inflow associated with the amount received from the sale of a portion of the company's business, for example a segment, division, branch or other business, during the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3179-108585 + Details
Name: | us-gaap_ProceedsFromDivestitureOfBusinesses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=aa_EastalcoAluminumSmelterSiteMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=stpr_MD
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=aa_WarrickRollingMillMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DisposalGroupClassificationAxis=us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=aa_ElementalEnvironmentalSolutionsLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |