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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Earnings Per Share [Abstract]
Net income attributable to Alcoa Corporation	$ 549	$ 309	$ 1,018	$ 484
Average shares outstanding – basic	182	187	183	186
Effect of dilutive securities:
Stock units	4	3	4	3
Average shares outstanding – diluted	186	190	187	189