Segment Information - Schedule of Operating Results of Alcoa's Reportable Segments (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	$ 236	$ 784	$ 2,193	$ 1,978
Depreciation, depletion, and amortization	144	149	453	480
Equity (loss) income	(23)	37	52	72
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	3,476	3,636	11,669	10,406
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	609	529	1,866	1,605
Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	2,867	3,107	9,803	8,801
Bauxite [Member]
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	15	23	58	123
Depreciation, depletion, and amortization	31	30	101	119
Bauxite [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	240	228	652	689
Bauxite [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	181	172	516	536
Bauxite [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	59	56	136	153
Alumina [Member]
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	69	148	674	499
Depreciation, depletion, and amortization	43	47	142	143
Equity (loss) income	(18)	(1)	(22)	(7)
Alumina [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	1,250	1,105	4,089	3,260
Alumina [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	418	349	1,325	1,056
Alumina [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	832	756	2,764	2,204
Aluminum [Member]
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	152	613	1,461	1,356
Depreciation, depletion, and amortization	70	72	210	218
Equity (loss) income	(5)	38	74	79
Aluminum [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	1,986	2,303	6,928	6,457
Aluminum [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	10	8	25	13
Aluminum [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	$ 1,976	$ 2,295	$ 6,903	$ 6,444