Acquisitions and Divestitures - Additional Information (Detail) $ in Millions					12 Months Ended
	Sep. 15, 2024 USD ($) shares	Sep. 12, 2024 USD ($)	Aug. 01, 2024 USD ($) shares	Jul. 31, 2024 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Jul. 31, 2024 $ / shares
Business Disposition [Line Items]
Deferred tax assets					$ 3,423	$ 3,240
Acquisition of cash			$ 9
Alcoa Corporation [Member]
Business Disposition [Line Items]
Ownership interest in joint venture					25.10%
Carrying value of investment					$ 544
Alumina Limited [Member]
Business Disposition [Line Items]
Business acquisition, shares outstanding | shares			2,760,056,014
Exchange ratio value per share | $ / shares								$ 1.45
Aggregate purchase consideration				$ 2,700
Noncontrolling interest			$ 1,472
Other current liabilities			1
Net assets acquired			1,216
Acquisition of noncontrolling interest			$ 1,099
Alumina Limited [Member] | Aluminum Segment [Member]
Business Disposition [Line Items]
Ownership interest in joint venture			55.00%
Alumina Limited [Member] | Additional Capital [Member]
Business Disposition [Line Items]
Transaction costs			$ 32
Alumina Limited [Member] | Common Stock [Member]
Business Disposition [Line Items]
Business acquisition, shares issued | shares			78,772,422
Alumina Limited [Member] | Nonvoting Convertible Preferred Stock [Member]
Business Disposition [Line Items]
Business acquisition, shares outstanding | shares			141,625,403
Business acquisition, shares issued | shares			4,041,989
Alumina Limited [Member] | Scheme Implementation Deed [Member]
Business Disposition [Line Items]
Business acquision, number of shares | shares			4
Assumption of indebtedness			$ 385
Deferred tax assets			$ 121		95
Alumina Limited [Member] | Scheme Implementation Deed [Member] | New Alcoa Preferred Stock [Member]
Business Disposition [Line Items]
Business acquisition, shares issued | shares			0.02854
Alumina Limited [Member] | Scheme Implementation Deed [Member] | Alcoa Common Stock [Member]
Business Disposition [Line Items]
Business acquisition, shares issued | shares			0.02854
Alumina Limited [Member] | AWAC [Member]
Business Disposition [Line Items]
Non-controlling interest, ownership percentage			40.00%
Alumina Limited [Member] | CHESS Depositary Interests [Member] | Scheme Implementation Deed [Member]
Business Disposition [Line Items]
Business acquisition, shares issued | shares			0.02854
Saudi Arabia Joint Venture [Member]
Business Disposition [Line Items]
Sale of ownership interest under agreement exchange for issuance shares | shares	85,977,547
Sale of ownership interest under agreement exchange for issuance shares value		$ 950
Ownership interest in joint venture	25.10%
Minimum holding period	3 years
Percentage of shares transferable	33.33%
Sale of ownership interest under agreement exchange for cash	$ 150
Warrick Rolling Mill [Member] | Disposal Group, Held-for-Sale, Not Discontinued Operations [Member]
Business Disposition [Line Items]
Estimated liabilities for future site separation commitment charge					32	17	$ 8
Payments against the reserve					35	$ 52	$ 37
Remaining reserve					$ 8