Earnings Per Share - Schedule of Computation of Basic and Diluted EPS Attributable to Alcoa Corporation Common Shareholders (Detail) - shares shares in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Earnings Per Share [Abstract]
Weighted average common shares outstanding - basic	232	178	197	178
Effect of dilutive securities:
Stock units	2
Weighted average common shares outstanding - diluted	234	178	197	178

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Number of additional shares included in diluted EPS for potentially dilutive effect of nonvested equity-based payment award containing forfeitable rights to dividends or dividend equivalents, whether paid or unpaid.

+ References

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

+ References

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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