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		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Earnings Per Share [Abstract]
Net Income (Loss)	$ 20	$ (102)	$ (232)	$ (333)
Average shares outstanding – basic	180	178	179	178
Effect of dilutive securities:
Stock units	1
Average shares outstanding – diluted	181	178	179	178