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		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Earnings Per Share [Abstract]
Net Income (Loss)	$ (168)	$ (746)	$ (501)	$ 272
Average shares outstanding – basic	178	179	178	182
Effect of dilutive securities:
Stock units				4
Average shares outstanding – diluted	178	179	178	186