Debt instrument redemption period.

No definition available.

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

- Definition

Extended maturity date of credit facility.

+ References

No definition available.

+ Details

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Namespace Prefix:	aa_
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Balance Type:	na
Period Type:	duration

- Definition

Repurchase of inventory related to agreement.

+ References

No definition available.

+ Details

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

- Definition

Short term borrowings of inventory related to agreement.

+ References

No definition available.

+ Details

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

- Definition

Date the debt agreement requires the first payment to be made, in YYYY-MM-DD format.

+ References

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

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

+ Details

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

- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

+ References

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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- Definition

The fair value of line of credit assumed in noncash investing or financing activities.

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- Definition

Date the credit facility terminates, in YYYY-MM-DD format.

+ References

+ Details

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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- Definition

The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.

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- Definition

The cash inflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer.

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- Definition

The cash outflow for the settlement of obligation drawn from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer.

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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Debt - Additional Information (Detail) ¥ in Millions			1 Months Ended	3 Months Ended		6 Months Ended
Debt - Additional Information (Detail) ¥ in Millions	Aug. 01, 2024 USD ($)	Apr. 26, 2024	Mar. 31, 2024 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2024 JPY (¥)	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)	Apr. 30, 2023 USD ($)
Debt Instrument [Line Items]
Short-term borrowings				$ 31,000,000		$ 31,000,000			$ 56,000,000
Borrowings of inventory related to agreement				24,000,000		45,000,000		$ 25,000,000
Repurchase of inventory related to agreement				$ 45,000,000	$ 15,000,000	$ 70,000,000		15,000,000
Alcoa Nederland Holding BV [Member] \| 7.125% Notes, due 2031 [Member]
Debt Instrument [Line Items]
Letters of credit			$ 750,000,000
Proceeds from issuance of public debt offering			$ 737,000,000
Senior notes, interest percentage			7.125%
Debt instrument, frequency of periodic payment						semi-annually	semi-annually
Debt instrument, date of first required payment			Sep. 15, 2024
Alcoa Nederland Holding BV [Member] \| 7.125% Notes, due 2031 [Member] \| After March 15, 2027 [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt instrument redemption period						10 days	10 days
Alcoa Nederland Holding BV [Member] \| 7.125% Notes, due 2031 [Member] \| After March 15, 2027 [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument redemption period						60 days	60 days
Debt instrument redemption price percentage						103.563%	103.563%
Alcoa Nederland Holding BV [Member] \| 7.125% Notes, due 2031 [Member] \| Change in Control [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument redemption price percentage						101.00%	101.00%
Alcoa Nederland Holding BV [Member] \| 4.125% Notes, due 2029 [Member]
Debt Instrument [Line Items]
Senior notes, interest percentage				4.125%		4.125%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Letters of credit				$ 0		$ 0			0
Amounts borrowed under the credit facility				0	0	0		0
Line of credit facility, outstanding borrowings				1,250,000,000		1,250,000,000
$250 Japanese Yen Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Letters of credit				0		0			$ 0
Amounts borrowed under the credit facility				$ 0	$ 0	201,000,000	¥ 29,686	$ 0
Amounts repaid under the credit facility						$ 196,000,000	¥ 29,686
Unsecured revolving credit facility										$ 250,000,000
Credit facility expiration date						Apr. 30, 2025	Apr. 30, 2025
Extended maturity date of credit facility		2025-04
Alumina Limited Revolving Credit Facility [Member] \| Subsequent Event [Member]
Debt Instrument [Line Items]
Unsecured revolving credit facility	$ 500,000,000
Line of credit assumed	385,000,000
Alumina Limited Revolving Credit Facility [Member] \| Subsequent Event [Member] \| Due in October 2025 [Member]
Debt Instrument [Line Items]
Unsecured revolving credit facility	$ 100,000,000
Extended maturity date of credit facility	2025-10
Alumina Limited Revolving Credit Facility [Member] \| Subsequent Event [Member] \| Due in January 2026 [Member]
Debt Instrument [Line Items]
Unsecured revolving credit facility	$ 150,000,000
Extended maturity date of credit facility	2026-01
Alumina Limited Revolving Credit Facility [Member] \| Subsequent Event [Member] \| Due in July 2026 [Member]
Debt Instrument [Line Items]
Unsecured revolving credit facility	$ 150,000,000
Extended maturity date of credit facility	2026-07
Alumina Limited Revolving Credit Facility [Member] \| Subsequent Event [Member] \| Due in June 2027 [Member]
Debt Instrument [Line Items]
Unsecured revolving credit facility	$ 100,000,000
Extended maturity date of credit facility	2027-06