Earnings Per Share - Schedule of Computation of Basic and Diluted EPS Attributable to Alcoa Corporation Common Shareholders (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Earnings Per Share [Abstract]
Net income attributable to Alcoa Corporation	$ 469	$ 175
Average shares outstanding – basic	184	186
Effect of dilutive securities:
Stock units	4	3
Average shares outstanding – diluted	188	189

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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