Contingencies and Commitments - Additional Information - 1 (Detail) R$ in Millions, $ in Millions, $ in Millions					1 Months Ended											3 Months Ended	9 Months Ended		12 Months Ended
	Oct. 01, 2024 USD ($)	Oct. 01, 2024 AUD ($)	Sep. 17, 2020 USD ($)	Sep. 17, 2020 AUD ($)	Aug. 31, 2022 USD ($)	Aug. 31, 2022 BRL (R$)	Jul. 31, 2022 USD ($)	Jul. 31, 2022 BRL (R$)	Mar. 31, 2022 USD ($)	Mar. 31, 2022 BRL (R$)	Feb. 28, 2022 USD ($)	Feb. 28, 2022 BRL (R$)	Mar. 31, 2013 USD ($)	May 31, 2012 USD ($)	May 31, 2012 BRL (R$)	Sep. 30, 2020 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2024 BRL (R$)	Dec. 31, 2012 USD ($)	Dec. 31, 2012 BRL (R$)	Sep. 30, 2024 AUD ($)	Jul. 31, 2024	Dec. 31, 2023 USD ($)	Dec. 31, 2023 AUD ($)	Jul. 31, 2022 BRL (R$)	Feb. 28, 2022 BRL (R$)	Sep. 30, 2020 AUD ($)	Jul. 07, 2020 USD ($)	Jul. 07, 2020 AUD ($)	Mar. 31, 2013 BRL (R$)	Dec. 31, 2012 BRL (R$)
Loss Contingencies [Line Items]
Other noncurrent liabilities and deferred credits																	$ 632						$ 568
AofA [Member] | Subsequent Event [Member]
Loss Contingencies [Line Items]
Bank guarantee delivered	$ 69	$ 100
Australian Taxation Office [Member] | Foreign Jurisdiction [Member] | AofA [Member]
Loss Contingencies [Line Items]
Additional income tax payable, exclusive of interest and penalties																												$ 147	$ 214
Notices include claims for compounded interest on the tax amount																												$ 488	$ 707
Proposed administrative penalties			$ 88	$ 128
Payment of dispute resolution practices income tax percentage																50.00%
Assessed income tax amount exclusive of interest and penalties																$ 74											$ 107
Payment amount refund percentage																50.00%
Other noncurrent liabilities and deferred credits																	222				$ 322		$ 199	$ 293
Tax assessment deposit																	74				$ 107
Alcoa World Alumina Brasil [Member] | Brazilian Federal Revenue Office [Member]
Loss Contingencies [Line Items]
Disallowed tax credits							$ 13				$ 4		$ 110												R$ 66	R$ 19				R$ 220
Percentage of penalty of the gross disallowed amount													50.00%
Value added tax receivable					$ 6	R$ 31	$ 10	R$ 53	$ 9	R$ 44	$ 14	R$ 65		$ 41	R$ 82
Federal value added tax credits																			$ 136												R$ 273
Value added tax refund received																			$ 68	R$ 136
Alcoa Corporation [Member] | AWAC [Member]
Loss Contingencies [Line Items]
Ownership interest percentage																						60.00%
Minimum [Member] | Alcoa World Alumina Brasil [Member] | Brazilian Federal Revenue Office [Member]
Loss Contingencies [Line Items]
Charge recorded in provision for income taxes to establish liability for estimated loss																	0
Maximum [Member] | Alcoa World Alumina Brasil [Member] | Brazilian Federal Revenue Office [Member]
Loss Contingencies [Line Items]
Charge recorded in provision for income taxes to establish liability for estimated loss																	$ 56	R$ 305