Segment Information - Schedule of Operating Results of Alcoa's Reportable Segments (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	$ 143	$ 954	$ 430	$ 1,969
Depreciation, depletion, and amortization	148	155	295	309
Equity (loss) income	(27)	35	(101)	75
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	3,083	4,141	6,174	7,847
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	401	491	825	911
Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	2,682	3,650	5,349	6,936
Alumina [Member]
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	33	358	136	660
Depreciation, depletion, and amortization	80	84	157	169
Equity (loss) income	(11)	(5)	(28)	(4)
Alumina [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	1,291	1,594	2,569	2,905
Alumina [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	397	483	818	896
Alumina [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	894	1,111	1,751	2,009
Aluminum [Member]
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	110	596	294	1,309
Depreciation, depletion, and amortization	68	71	138	140
Equity (loss) income	(16)	40	(73)	79
Aluminum [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	1,792	2,547	3,605	4,942
Aluminum [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	4	8	7	15
Aluminum [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	$ 1,788	$ 2,539	$ 3,598	$ 4,927