Subsequent Events - Additional Information (Detail) - Subsequent Event [Member] $ in Millions	1 Months Ended
Apr. 30, 2023 USD ($) Retiree
Subsequent Event [Line Items]
Number of retirees \| Retiree	500
Plan obligations and plan assets completed date	Apr. 18, 2023
Settlements after tax	$ (13)
Plan assets	235
Settlements	$ (18)

Defined benefit plan benefit obligation completed date.

No definition available.

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Namespace Prefix:	aa_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Defined benefit plan number of plan retirees.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Defined benefit plan recognized net gain loss due to settlements after tax.

+ References

No definition available.

+ Details

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Namespace Prefix:	aa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(7)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 45
-Paragraph 3A
-URI https://asc.fasb.org/extlink&oid=123453770&loc=SL108413299-114919

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)(7)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of payment, which decreases plan assets of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract.

+ References

+ Details

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Balance Type:	credit
Period Type:	duration

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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