Master Trust - Schedule of Master Trust Investments Including Gain and Losses on Investment (Details) - EBP 004 & 003 - EBP, Nonconsolidated, Master Trust	12 Months Ended
Dec. 31, 2025 USD ($)
EBP, Master Trust [Line Items]
Net investment income	$ 94,533,999
Interest	1,765,308
Net investment income from Savings Plans Master Trust for Alcoa USA Corporation investments	105,595,210
Investments in Stock Fund
EBP, Master Trust [Line Items]
Net investment income	5,102,631
Dividends	132,787
Shares of Registered Investment Companies
EBP, Master Trust [Line Items]
Net investment income	63,747,130
Dividends	8,846,047
Self-Directed Brokerage Accounts
EBP, Master Trust [Line Items]
Net investment income	4,136,642
Dividends	317,069
Commingled Trusts
EBP, Master Trust [Line Items]
Net investment income	$ 21,547,596

Amount of increase (decrease) in net asset available for benefit from realized and unrealized gain (loss) on investment held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

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