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, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	$ 3,053	$ 1,317	$ 1,626
Depreciation, depletion, and amortization	640	629	680
Equity income (loss)	120	(30)	(43)
Capital expenditures	380	341
Equity investments	1,182	1,032
Total assets	12,066	12,015
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	14,456	11,485	12,907
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	2,315	2,221	2,557
Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	12,141	9,264	10,350
Bauxite [Member]
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	172	495	504
Depreciation, depletion, and amortization	153	135	120
Capital expenditures	95	127
Equity investments	234	222
Total assets	1,430	1,468
Bauxite [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	947	1,213	1,276
Bauxite [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	711	941	979
Bauxite [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	236	272	297
Alumina [Member]
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	1,002	497	1,097
Depreciation, depletion, and amortization	198	172	214
Equity income (loss)	4	(23)	6
Capital expenditures	178	103
Equity investments	270	264
Total assets	4,385	4,333
Alumina [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	4,725	3,895	4,811
Alumina [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	1,586	1,268	1,561
Alumina [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	3,139	2,627	3,250
Aluminum [Member]
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA	1,879	325	25
Depreciation, depletion, and amortization	289	322	346
Equity income (loss)	116	(7)	(49)
Capital expenditures	107	111
Equity investments	678	546
Total assets	6,251	6,214
Aluminum [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	8,784	6,377	6,820
Aluminum [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	18	12	17
Aluminum [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	$ 8,766	$ 6,365	$ 6,803