Segment and Related Information - Schedule of Operating Results, Capital Expenditures and Assets of Alcoa's Reportable Segments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Adjusted operating costs	$ 8,598	$ 8,768	$ 9,348
Other segment items	3,508	2,699	2,566
Segment Adjusted EBITDA	2,065	734	2,280
Depreciation, depletion, and amortization	620	610	595
Equity income (loss)	17	(154)	9
Capital expenditures	564	521	473
Equity investments	966	964
Total assets	12,267	12,007
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	14,171	12,201	14,194
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	2,279	1,663	1,735
Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	11,892	10,538	12,459
Alumina [Member]
Segment Reporting Information [Line Items]
Adjusted operating costs	3,110	3,487	3,745
Other segment items	2,407	1,501	899
Segment Adjusted EBITDA	1,408	273	788
Depreciation, depletion, and amortization	348	333	312
Equity income (loss)	22	(48)	(39)
Capital expenditures	367	323	320
Equity investments	420	395
Total assets	6,138	6,153
Alumina [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	6,925	5,261	5,432
Alumina [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	2,263	1,648	1,708
Alumina [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	4,662	3,613	3,724
Aluminum [Member]
Segment Reporting Information [Line Items]
Adjusted operating costs	5,488	5,281	5,603
Other segment items	1,101	1,198	1,667
Segment Adjusted EBITDA	657	461	1,492
Depreciation, depletion, and amortization	272	277	283
Equity income (loss)	(5)	(106)	48
Capital expenditures	197	198	153
Equity investments	546	569
Total assets	6,129	5,854
Aluminum [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	7,246	6,940	8,762
Aluminum [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	16	15	27
Aluminum [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	$ 7,230	$ 6,925	$ 8,735