Segment Information - Schedule of Operating Results of Alcoa's Reportable Segments (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	$ 287	$ 1,015
Depreciation, depletion, and amortization	147	154
Equity (loss) income	(74)	40
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	3,091	3,706
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	424	420
Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	2,667	3,286
Alumina [Member]
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	103	302
Depreciation, depletion, and amortization	77	85
Equity (loss) income	(17)	1
Alumina [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	1,278	1,311
Alumina [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	421	413
Alumina [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	857	898
Aluminum [Member]
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	184	713
Depreciation, depletion, and amortization	70	69
Equity (loss) income	(57)	39
Aluminum [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	1,813	2,395
Aluminum [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	3	7
Aluminum [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	$ 1,810	$ 2,388