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, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Earnings Per Share [Abstract]
Net Income (Loss)	$ (102)	$ 549	$ (333)	$ 1,018
Average shares outstanding – basic	178	182	178	183
Effect of dilutive securities:
Stock units		4		4
Average shares outstanding – diluted	178	186	178	187