XML 49 R38.htm IDEA: XBRL DOCUMENT
v3.21.2

Basis of Presentation - Additional Information (Detail) - AWAC [Member] | Jun. 30, 2021
--- | ---
Alumina Limited [Member] |
Basis Of Presentation [Line Items] |
Non-controlling interest, ownership percentage | 40.00%
Alcoa Corporation [Member] |
Basis Of Presentation [Line Items] |
Ownership interest percentage | 60.00%

X
- Definition Basis of Presentation [Line Items] + References No definition available. + Details
Name: | aa_BasisOfPresentationLineItems
Namespace Prefix: | aa_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity. + References No definition available. + Details
Name: | us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The parent entity's interest in net assets of the subsidiary, expressed as a percentage. + References No definition available. + Details
Name: | us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | srt_OwnershipAxis=aa_AlcoaWorldAluminaAndChemicalsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=aa_AluminaLimitedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=aa_AlcoaCorporationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |