v3.26.1
Master Trust - Schedule of Net Assets of Master Trust and Plans' Interest (Details) - USD ($)
Dec. 31, 2025
Dec. 31, 2024
EBP 004 & 003 | EBP, Nonconsolidated, Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value $ 649,325,069 $ 604,812,482
Investment contracts at contract value 52,060,754 58,433,249
Total value of interest in Savings Plans Master Trust for Alcoa USA Corporation 701,385,823 663,245,731
EBP 004 & 003 | Investments in Stock Fund | EBP, Nonconsolidated, Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value 14,083,850 11,392,632
EBP 004 & 003 | Shares of Registered Investment Companies | EBP, Nonconsolidated, Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value 460,305,683 406,364,768
EBP 004 & 003 | Commingled Trusts | EBP, Nonconsolidated, Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value 150,358,924 164,419,005
EBP 004 & 003 | Self-Directed Brokerage Accounts | EBP, Nonconsolidated, Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value 24,576,612 22,636,077
EBP 004 | EBP, Nonconsolidated, Plan Interest in Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value 237,510,239 214,127,218
Investment contracts at contract value 23,141,275 26,650,341
Total value of interest in Savings Plans Master Trust for Alcoa USA Corporation 260,651,514 240,777,559
EBP 004 | Investments in Stock Fund | EBP, Nonconsolidated, Plan Interest in Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value 4,908,261 4,435,218
EBP 004 | Shares of Registered Investment Companies | EBP, Nonconsolidated, Plan Interest in Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value 164,861,080 130,413,866
EBP 004 | Commingled Trusts | EBP, Nonconsolidated, Plan Interest in Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value 61,237,452 72,465,064
EBP 004 | Self-Directed Brokerage Accounts | EBP, Nonconsolidated, Plan Interest in Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value 6,503,446 6,813,070
EBP 003 | EBP, Nonconsolidated, Plan Interest in Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value 411,814,830 390,685,264
Investment contracts at contract value 28,919,479 31,782,908
Total value of interest in Savings Plans Master Trust for Alcoa USA Corporation 440,734,309 422,468,172
EBP 003 | Investments in Stock Fund | EBP, Nonconsolidated, Plan Interest in Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value 9,175,589 6,957,414
EBP 003 | Shares of Registered Investment Companies | EBP, Nonconsolidated, Plan Interest in Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value 295,444,603 275,950,902
EBP 003 | Commingled Trusts | EBP, Nonconsolidated, Plan Interest in Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value 89,121,472 91,953,941
EBP 003 | Self-Directed Brokerage Accounts | EBP, Nonconsolidated, Plan Interest in Master Trust    
EBP, Master Trust [Line Items]    
Investments at fair value $ 18,073,166 $ 15,823,007