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, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Earnings Per Share [Abstract]
Net (loss) income attributable to Alcoa Corporation	$ (746)	$ 337	$ 272	$ 821
Average shares outstanding – basic	179	187	182	187
Effect of dilutive securities:
Stock units		4	4	3
Average shares outstanding – diluted	179	191	186	190