v3.26.1
Fair Value Measurements - Schedule of Fair Value Hierarchy the Plans Assets at Fair Value (Details) - EBP 004 & 003 - USD ($)
Dec. 31, 2025
Dec. 31, 2024
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation $ 649,325,069 $ 604,812,482
Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 498,552,361 440,021,586
Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 10,018 9,998
Assets Measured at Net Asset Value    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 150,762,690 [1] 164,780,898 [2]
Alcoa Corporation Common Stock    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 13,680,084 11,030,739
Alcoa Corporation Common Stock | Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 13,680,084 11,030,739
Alcoa Corporation Common Stock | Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 0 0
Alcoa Corporation Common Stock | Assets Measured at Net Asset Value    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 0 [1] 0 [2]
Registered Investment Companies    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 460,305,683 406,364,768
Registered Investment Companies | Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 460,305,683 406,364,768
Registered Investment Companies | Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 0 0
Registered Investment Companies | Assets Measured at Net Asset Value    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 0 [1] 0 [2]
Commingled Trusts    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 150,762,690 164,780,898
Commingled Trusts | Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 0 0
Commingled Trusts | Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 0 0
Commingled Trusts | Assets Measured at Net Asset Value    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 150,762,690 [1] 164,780,898 [2]
Self-Directed Brokerage Accounts    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 24,576,612 22,636,077
Self-Directed Brokerage Accounts | Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 24,566,594 22,626,079
Self-Directed Brokerage Accounts | Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation 10,018 9,998
Self-Directed Brokerage Accounts | Assets Measured at Net Asset Value    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation $ 0 [1] $ 0 [2]
[1] In accordance with Subtopic 820-10, certain investments that were measured at net asset value per share (or its equivalent) have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the line items presented in the Statements of Individual Plan Net Assets Available for Benefits.
[2] In accordance with Subtopic 820-10, certain investments that were measured at net asset value per share (or its equivalent) have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the line items presented in the Statements of Individual Plan Net Assets Available for Benefits.