Segment Information - Additional Information (Detail)	3 Months Ended
Mar. 31, 2025 Segment
Segment Reporting [Abstract]
Number of operating segments	2
Number of reportable segments	2
Segment Reporting, CODM, Individual Title and Position or Group Name [Extensible Enumeration]	srt:ChiefExecutiveOfficerMember, srt:PresidentMember
Segment Reporting, CODM, Profit (Loss) Measure, How Used, Description	The Company calculates Segment Adjusted EBITDA as Total sales (third-party and intersegment) minus the following items: Cost of goods sold; Selling, general administrative, and other expenses; and Research and development expenses. Alcoa Corporation’s Segment Adjusted EBITDA may not be comparable to similarly titled measures of other companies. The CODM regularly reviews Segment Adjusted EBITDA to assess performance and allocate resources (including employees, property, and financial or capital resources) in the planning and strategic review process.

2

Segment Reporting, CODM, Profit (Loss) Measure, How Used, Description

The Company calculates Segment Adjusted EBITDA as Total sales (third-party and intersegment) minus the following items: Cost of goods sold; Selling, general administrative, and other expenses; and Research and development expenses. Alcoa Corporation’s Segment Adjusted EBITDA may not be comparable to similarly titled measures of other companies. The CODM regularly reviews Segment Adjusted EBITDA to assess performance and allocate resources (including employees, property, and financial or capital resources) in the planning and strategic review process.