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Number of employees.

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Payments related to other costs.

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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Includes expenses related to certain asset retirement obligations.

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Amount of cash payments made as the result of exit or disposal activities. Excludes payments associated with a discontinued operation or an asset retirement obligation.

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Carrying amount as of the balance sheet date of known and estimated costs associated with exit from or disposal of business activities or restructurings pursuant to a duly authorized plan, which are expected to be paid after one year or beyond the next operating cycle, if longer. Costs of such activities include those for one-time termination benefits, termination of an operating lease or other contract, consolidating or closing facilities, and relocating employees, and costs associated with an ongoing benefit arrangement, but excludes costs associated with the retirement of a long-lived asset.

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Amount of expenses for special or contractual termination benefits provided to current employees involuntarily terminated under a benefit arrangement associated exit or disposal activities pursuant to an authorized plan. Excludes expenses related to one-time termination benefits, a discontinued operation or an asset retirement obligation.

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Restructuring and Other Charges, Net - Additional Information (Detail) $ in Millions	3 Months Ended				9 Months Ended		12 Months Ended
	Mar. 31, 2025 USD ($) Employees	Dec. 31, 2024 USD ($)	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Dec. 31, 2025 USD ($) Employees	Dec. 31, 2024 USD ($)	Dec. 31, 2024 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges	$ 5			$ 202
Cash payment for restructuring	49						$ 183
Restructuring and other charges, net	$ 5			202
Kwinana Refinery [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges				197
Severance costs				41
Number of employees \| Employees	240
Asset impairments				5
Payments related to other costs	$ 41
Restructuring and other charges, net		$ 82	$ 8	197
Kwinana Refinery [Member] \| Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Number of employees \| Employees					50
Remaining cash outlays expected through 2025					$ 100
Alcoa Corporation [Member]
Restructuring Cost and Reserve [Line Items]
Noncurrent portion of the reserve	9	$ 8				$ 8	8
2024 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net				202
2025 Restructuring Plans Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	5
Certain Employee Obligations [Member] \| San Ciprian Aluminum Smelter [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges	3
Severance and Employee Termination Costs [Member]
Restructuring Cost and Reserve [Line Items]
Cash payment for restructuring	1						38
Other Exit Costs [Member]
Restructuring Cost and Reserve [Line Items]
Cash payment for restructuring	48						$ 145
Water Management Costs [Member] \| Kwinana Refinery [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges				123
Other Restructuring [Member] \| Kwinana Refinery [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges				136		96
Asset Retirement Obligations [Member] \| Kwinana Refinery [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges				15		$ (6)
Take Or-Pay Contracts [Member] \| Kwinana Refinery [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring And Other Charges				$ 13
Contract Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges, net	$ 2