Investments - Summary of Balance Sheet Information for Alcoa Corporation's Equity Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Current assets	$ 5,026	$ 4,520
Current liabilities	3,223	2,761
Ma'aden Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Current assets	1,748	1,099
Noncurrent assets	7,330	7,648
Current liabilities	956	794
Noncurrent liabilities	5,018	5,347
Mining [Member]
Schedule of Equity Method Investments [Line Items]
Current assets	142	143
Noncurrent assets	852	828
Current liabilities	158	206
Noncurrent liabilities	331	331
Energy [Member]
Schedule of Equity Method Investments [Line Items]
Current assets	96	119
Noncurrent assets	316	401
Current liabilities	17	27
Noncurrent liabilities	27	113
Other [Member]
Schedule of Equity Method Investments [Line Items]
Current assets	246	219
Noncurrent assets	755	757
Current liabilities	95	66
Noncurrent liabilities	$ 73	$ 62