Asset Retirement Obligations - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022
Asset Retirement Obligations [Line Items]
Current liability	$ 217	$ 117
Liabilities incurred	254	224
Reversals of previously recorded liabilities	(8)	(12)
Restructuring and Other Charges [Member]
Asset Retirement Obligations [Line Items]
Liabilities incurred		34
Cost of Goods Sold [Member]
Asset Retirement Obligations [Line Items]
Liabilities incurred	15	72
Magnesium Smelter Facility in Addy [Member]
Asset Retirement Obligations [Line Items]
Liabilities incurred		15
Bauxite Residue Areas [Member]
Asset Retirement Obligations [Line Items]
Liabilities incurred	97	81
Mine Areas [Member]
Asset Retirement Obligations [Line Items]
Liabilities incurred	87	79
Intalco Smelter [Member]
Asset Retirement Obligations [Line Items]
Liabilities incurred	36
Intalco Smelter [Member] \| Restructuring and Other Charges [Member]
Asset Retirement Obligations [Line Items]
Liabilities incurred	41
Spent Pot Lining Treatment and Disposal [Member]
Asset Retirement Obligations [Line Items]
Liabilities incurred	23	28
Non-Operating Bauxite Residue Areas [Member]
Asset Retirement Obligations [Line Items]
Liabilities incurred	10
Bauxite Residue Areas Related to Water Management [Member]
Asset Retirement Obligations [Line Items]
Liabilities incurred		18
Demolition Projects [Member]
Asset Retirement Obligations [Line Items]
Liabilities incurred	1	3
Reversals of previously recorded liabilities	$ 8	$ 12

Asset Retirement obligations.

No definition available.

Name:	aa_AssetRetirementObligationsLineItems
Namespace Prefix:	aa_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Current portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 410
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481850/410-20-50-1

+ Details

Name:	us-gaap_AssetRetirementObligationCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of asset retirement obligations incurred during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 410
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481850/410-20-50-1

+ Details

Name:	us-gaap_AssetRetirementObligationLiabilitiesIncurred
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 410
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(4)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481850/410-20-50-1

+ Details

Name:	us-gaap_AssetRetirementObligationRevisionOfEstimate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_IncomeStatementLocationAxis=aa_RestructuringAndOtherChargesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_CostOfSalesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=aa_MagnesiumSmelterFacilityInAddyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=aa_BauxiteResidueAreasMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=aa_MineAreasMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=aa_IntalcoSmelterMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=aa_SpentPotLiningTreatmentAndDisposalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=aa_NonOperatingBauxiteResidueAreasMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=aa_BauxiteResidueAreasRelatedToWaterManagementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=aa_DemolitionProjectsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: