Investments - Summary of Profit and Loss Information for Alcoa Corporation's Equity Investments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Net income (loss)	$ 570	$ (14)	$ (853)
Ma'aden Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Sales	3,127	2,279	3,185
Cost of goods sold	2,083	1,829	2,722
Net income (loss)	495	(108)	(198)
Equity in net income (loss) of affiliated companies, before reconciling adjustments	124	(27)	(50)
Other	(8)	(7)	3
Alcoa Corporation’s equity in net (loss) income of affiliated companies	116	(34)	(47)
Mining [Member]
Schedule of Equity Method Investments [Line Items]
Sales	794	841	846
Cost of goods sold	571	543	580
Net income (loss)	30	46	35
Equity in net income (loss) of affiliated companies, before reconciling adjustments	18	23	16
Other	5	(1)	5
Alcoa Corporation’s equity in net (loss) income of affiliated companies	23	22	21
Energy [Member]
Schedule of Equity Method Investments [Line Items]
Sales	264	238	269
Cost of goods sold	135	107	143
Net income (loss)	114	74	107
Equity in net income (loss) of affiliated companies, before reconciling adjustments	45	31	42
Other	(1)	2	1
Alcoa Corporation’s equity in net (loss) income of affiliated companies	44	33	43
Other [Member]
Schedule of Equity Method Investments [Line Items]
Sales	404	316	159
Cost of goods sold	365	283	151
Net income (loss)	(42)	(24)	(28)
Equity in net income (loss) of affiliated companies, before reconciling adjustments	(20)	(11)	(13)
Other	25	14	16
Alcoa Corporation’s equity in net (loss) income of affiliated companies	$ 5	$ 3	$ 3