75000 - Document - Document and Entity Information link:presentationLink link:calculationLink link:definitionLink 75010 - Statement - Statements of Individual Plan Net Assets Available for Benefits link:presentationLink link:calculationLink link:definitionLink 75020 - Statement - Statements of Changes in Individual Plan Net Assets Available for Benefits link:presentationLink link:calculationLink link:definitionLink 75030 - Disclosure - Description of Plans link:presentationLink link:calculationLink link:definitionLink 75040 - Disclosure - Summary of Accounting Policies link:presentationLink link:calculationLink link:definitionLink 75050 - Disclosure - Master Trust link:presentationLink link:calculationLink link:definitionLink 75060 - Disclosure - Fair Value Measurements link:presentationLink link:calculationLink link:definitionLink 75070 - Disclosure - Investment Contracts link:presentationLink link:calculationLink link:definitionLink 75080 - Disclosure - Related-Party and Party-In-Interest Transactions link:presentationLink link:calculationLink link:definitionLink 75090 - Disclosure - Tax Status link:presentationLink link:calculationLink link:definitionLink 75100 - Disclosure - Subsequent Events link:presentationLink link:calculationLink link:definitionLink 75110 - Disclosure - Schedule of Assets (Held at End of Year) link:presentationLink link:calculationLink link:definitionLink 75120 - Disclosure - Summary of Accounting Policies (Policies) link:presentationLink link:calculationLink link:definitionLink 75130 - Disclosure - Master Trust (Tables) link:presentationLink link:calculationLink link:definitionLink 75140 - Disclosure - Fair Value Measurements (Tables) link:presentationLink link:calculationLink link:definitionLink 75150 - Disclosure - Description of Plans - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 75160 - Disclosure - Summary of Accounting Policies - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 75170 - Disclosure - Master Trust - Schedule of Net Assets of Master Trust and Plans' Interest (Details) link:presentationLink link:calculationLink link:definitionLink 75180 - Disclosure - Master Trust - Schedule of Master Trust Investments Including Gain and Losses on Investment (Details) link:presentationLink link:calculationLink link:definitionLink 75190 - Disclosure - Master Trust - Schedule of Master Trust Investments Including Gains and Losses on Investments (Parenthetical) (Details) link:presentationLink link:calculationLink link:definitionLink 75200 - Disclosure - Fair Value Measurements - Schedule of Fair Value Hierarchy the Plans Assets at Fair Value (Details) link:presentationLink link:calculationLink link:definitionLink 75210 - Disclosure - Investment Contracts - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 75220 - Disclosure - Related-Party and Party-In-Interest Transactions - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 75230 - Disclosure - Tax Status - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 75240 - Disclosure - Schedule of Assets (Held at End of Year) (Details) link:presentationLink link:calculationLink link:definitionLink EBP, Note Receivable from Participant, Account, Maximum Borrowing, to Total Account, Percentage Maximum allowable loan, percentage EBP, Master Trust [Abstract] EBP, Change in Net Asset Available for Benefit, Decrease from Administrative Expense Administrative expense fees EBP, Net Asset Available for Benefit Net assets available for benefits Net assets available for benefits, Beginning of year Net assets available for benefits, End of year Minimum [Member] Minimum EBP, Employer Contribution, Matching Percentage Employee benefit plan, matching employer contribution percentage EBP, Schedule of Asset Held for Investment [Table] EBP, Tax Status [Line Items] EBP, Payment to Participant [Policy Text Block] Benefit Payments to Participants EBP, Description of Plan and Accounting Change [Abstract] EBP, Fully Benefit-Responsive Investment Contract [Table] EBP, Investment, Plan Interest in Master Trust, Fair and Contract Value Total value of interest in Savings Plans Master Trust for Alcoa USA Corporation (Note 3) Document Period End Date Document Information [Table] Investments [Domain] EBP, Statement of Net Asset Available for Benefit [Abstract] EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Investment Income (Loss), after Investment Expense Total Plan interest in Savings Plans Master Trust for Alcoa USA Corporation investment income Total Plan interest in Savings Plans Master Trust for Alcoa USA Corporation investment income EBP, Employer Contribution, Receivable Employer contribution receivable Repayment of principal with guarantee of crediting rate Employee Benefit Plan, Repayment of Principal with Guarantee of Crediting Rate Employee benefit plan, repayment of principal with guarantee of crediting rate. EBP, Investment, Fair Value EBP, Investment, Fair Value, Total Total fair value of assets in Savings Plans Master Trust for Alcoa USA Corporation Investments at fair value EBP, Self-Directed Brokerage Account [Member] Self-Directed Brokerage Accounts EBP, Note Receivable from Participant Notes receivable from participants EBP, Fully Benefit-Responsive Investment Contract [Text Block] Investment Contracts EBP, Tax Status [Text Block] Tax Status EBP, Investment, Fair and Contract Value Total value of interest in Savings Plans Master Trust for Alcoa USA Corporation Employee Benefit Plan Participant Contribution Target Rate Employee benefit plan participant contribution target rate. Employee benefit plan participant contribution target rate EBP, Use of Estimate [Policy Text Block] Use of Estimates Master Trust EBP, Master Trust [Text Block] EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash and Noncash EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash and Noncash, Total Employer EBP, Investment, Contract Value EBP, Investment, Contract Value, Total Investment contracts at contract value (Note 5) Investment contracts at contract value EBP, Accounting Policy [Table] EBP, Other Investment [Member] Other investments EBP, Investment [Policy Text Block] Investment Valuation and Income Recognition Common Collective Trust [Member] Common Collective Trust Statistical Measurement [Axis] Employee Benefit Plan Employee Contribution to Plans Percentage of Eligible Compensation as Pre Tax or Roth After Tax Maximum Limit Employee contribution to plans percentage of eligible compensation as pre-tax or Roth after-tax maximum limit Employee benefit plan employee contribution to plans percentage of eligible compensation as pre-tax or Roth after-tax maximum limit. EBP, Participant Contribution, Receivable Participant contribution receivable Employee Benefit Plan Voting Rights [Policy Text Block] Employee benefit plan voting rights. Voting Rights EBP, Basis of Accounting [Policy Text Block] Basis of Accounting Registered Investment Companies [Member] Registered Investment Companies Member. Registered Investment Companies Other Security Investments [Member] Other Investments EBP, Investment, Fair Value and NAV [Table Text Block] Schedule of Fair Value Hierarchy the Plans Assets at Fair Value Transfers between plans, net EBP, Change in Net Asset Available for Benefit, Transfer to (from) Plan Loans to participants EBP, Asset Held for Investment, Participant Loan, after Deemed Distribution EBP, Fully Benefit-Responsive Investment Contract, Limitation on Transacting at Contract Value, Description Transacting at contract value, description Employee Benefit Plan Loan Processing Fee Deducted from Loan Amount Employee benefit plan loan processing fee deducted from loan amount. Employee benefit plan loan processing fee deducted from loan amount EBP, Change in Net Asset Available for Benefit, Increase Total additions Eligible employees in hourly plan to receive retiree medical savings contribution of per hour worked Eligible employees in hourly plan to receive retiree medical savings contribution of per hour worked. Shares of Registered Investment Companies [Member] Shares of registered investment companies. Shares of Registered Investment Companies Fair Value Hierarchy and NAV [Axis] Deductions EBP, Change in Net Asset Available for Benefit, Decrease [Abstract] EBP, Nonconsolidated, Plan Interest in Master Trust [Member] EBP, Nonconsolidated, Plan Interest in Master Trust Employee Benefit Plan Percentage of Participants Direct Contribution in Multiples into Various Investment Options Offered by Plans Employee benefit plan percentage of participants direct contribution in multiples into various investment options offered by plans. Percentage of participants direct contribution in multiples into various investment options offered by plans Employee Benefit Plan Employee Contribution to Non Roth After Tax Aggregate Maximum Percentage Employee contribution to non-Roth after tax aggregate maximum percentage Employee benefit plan employee contribution to non-Roth after tax aggregate maximum percentage. EBP, Description of Plan [Line Items] EBP, Change in Net Asset Available for Benefit, Increase from Contribution Total contributions Document Fiscal Period Focus Employee Benefit Plan, Employer Retirement Income Contribution Rate Employee benefit plan, employer retirement income contribution rate. Employee benefit plan employer retirement income contribution rate EBP, Employer, Common Stock [Member] Alcoa Corporation Common Stock EBP, Schedule of Asset Held for Investment [Abstract] EBP, Related Party and Party-in-Interest Transactions [Abstract] Maximum borrowing, amount EBP, Note Receivable from Participant, Account, Maximum Borrowing, Amount Fair Value, Inputs, Level 1 [Member] Level 1 Employee Benefit Plan Eligible Employee in Hourly Plan Defer Pre-Tax Saving Maximum Percentage of Amount Earned Employee benefit plan eligible employee in hourly plan defer pre-tax saving maximum percentage of amount earned. Eligible employee in hourly plan defer pre-tax saving maximum percentage of amount earned Investment Type [Axis] Investments at Stock Funds [Member] Investments at stock funds. Investments in Stock Fund Common Stock [Member] Common Stock Alcoa Corporation Common Stock Statistical Measurement [Domain] EBP, Fully Benefit-Responsive Investment Contract [Line Items] Entity Central Index Key EBP, Asset Held for Investment, Participant Loan, Interest Rate Interest rates for loans to participants (as a percent) Employee benefit plan participant loan, interest rate Summary of Accounting Policies EBP, Summary of Accounting Policy [Text Block] Current Fiscal Year End Date Fair Value, Inputs, Level 2 [Member] Level 2 EBP, Nonconsolidated, Master Trust [Member] EBP, Nonconsolidated, Master Trust EBP, Statement of Net Asset Available for Benefit [Table] EBP, Accounting Policy [Line Items] EBP, Investment, Fair Value and NAV [Abstract] Fair Value Hierarchy and NAV [Domain] EBP, Nonconsolidated, Master Trust and Plan Interest in Master Trust [Axis] Self-Directed Brokerage Accounts [Member] Self-directed brokerage accounts. Self-Directed Brokerage Accounts EBP, Related Party and Party-in-Interest Transactions [Text Block] Related-Party and Party-In-Interest Transactions EBP, Change in Net Asset Available for Benefit, Increase (Decrease) Net increase prior to Plan transfers EBP, Asset [Abstract] Document Type EBP, Description of Plan [Table] EBP, Change in Net Asset Available for Benefit, Increase from Interest Income on Investment Interest EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Total Participant Employee Benefit Plan Participant Contribution Partial Payout Employee benefit plan participant contribution partial payout. Employee benefit plan participant contribution partial payout EBP, Statement of Change in Net Asset Available for Benefit [Abstract] EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Gain (Loss) on Investment EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Gain (Loss) on Investment, Total Net investment income Employee Benefit Plan Pay for Performance Plan in Incremental Percentage Employee benefit plan pay for performance plan in incremental percentage Pay for performance plan in incremental percentage EBP, Asset Held for Investment, Plan Interest in Master Trust, Current Value Savings plans master trust current value EBP, Nonconsolidated, Master Trust and Plan Interest in Master Trust [Domain] Entity Registrant Name EBP, Related Party and Party-in-Interest Transactions [Table] EBP, Change in Net Asset Available for Benefit, Increase from Dividend Income on Investment Dividends earned on common stock Dividends EBP, Description of Plan [Text Block] Description of Plans EBP, Subsequent Event [Line Items] EBP, Subsequent Event [Table] EBP, Accounting Policy, Accounting Standard Update, and Change in Accounting Principle [Abstract] EBP, Plan Name Plan name EBP, Investment, Number of Shares EBP, number of plans owned EBP, Tax Determination Letter, Date EBP tax determination letter date Commingled Trusts [Member] Commingled Trusts Member. Commingled Trusts EBP, Plan Number Plan number EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment Net investment income from Savings Plans Master Trust for Alcoa USA Corporation investments EBP, Tax Status [Abstract] Employee Benefit Plan, Change In Net Asset Available For Benefit, Increase (Decrease), After Transfers To (From) Plan Employee benefit plan change in net asset available for benefit increase (decrease) after transfers to (from) plan. Net increase Employee Benefit Plan Note Receivable From Participant Prime Rate Employee benefit plan, note receivable from participant prime rate. Employee benefit plan note receivable from participant prime rate Employee Benefit Plan Participants Account Balance Receive Lump-Sum Distribution Employee benefit plan participants account balance receive lump-sum distribution. Employee benefit plan participants account balance receive lump-sum distribution EBP, Change in Net Asset Available for Benefit, Decrease from Payment to Participant Benefit payments to participants EBP, Receivable Total receivables EBP, Statement of Net Asset Available for Benefit [Line Items] Entity Tax Identification Number Minimum borrowing, amount EBP, Note Receivable from Participant, Account, Minimum Borrowing, Amount EBP, Note Receivable from Participant [Policy Text Block] Notes Receivable from Participants EBP 003 [Member] EBP 003. EBP 003 Salaried Plan Entity [Domain] Employee Benefit Plan Percentage of Increase by Participant Contribution To Eligible Compensation Employee benefit plan percentage of increase by participant contribution to eligible compensation. Employee benefit plan percentage of increase by participant contribution to eligible compensation Market value of purchases amount EBP, Investment Acquired, Excluding Plan Interest in Master Trust, Cost EBP, Schedule of Asset Held for Investment [Text Block] Schedule of Assets (Held at End of Year) EBP, Related Party and Party-in-Interest Transactions [Line Items] Maximum [Member] Maximum Employee Benefit Plan Administrative and Asset Management Expenses [Policy Text Block] Employee benefit plan administrative and asset management expenses. Administrative and Asset Management Expenses Employee Benefit Plan Dividends [Policy Text Block] Employee benefit plan dividends. Dividends EBP, Investment, Fair Value and NAV [Text Block] Fair Value Measurements EBP, Investment Sold, Excluding Plan Interest in Master Trust, Selling Price Market value of sales amount Document Fiscal Year Focus Alcoa Corporation Stock Fund EBP, Employer, Common Stock Fund [Member] Additions EBP, Change in Net Asset Available for Benefit, Increase [Abstract] EBP, Fully Benefit-Responsive Investment Contract, Limitation on Transacting at Contract Value, Not Probable [true false] Limitation on transacting at contract value, not probable [true false] EBP, Change in Net Asset Available for Benefit, Increase from Contribution [Abstract] Contributions EBP, Investment, Plan Interest in Master Trust, Contract Value Investment contracts at contract value (Note 5) EBP, Fully Benefit-Responsive Investment Contract [Abstract] EBP, Fully Benefit-Responsive Investment Contract, Termination, Description Investment contract, termination, description Amendment Flag EBP, Tax Determination Letter, Obtained [true false] EBP tax determination letter date obtained EBP, Subsequent Event [Text Block] Subsequent Events EBP, Tax Status [Table] Fair Value Measured at Net Asset Value Per Share [Member] Assets Measured at Net Asset Value EBP, Receivable [Abstract] Receivables EBP, Statement of Change in Net Asset Available for Benefit [Line Items] EBP, Master Trust [Table] Legal Entity [Axis] EBP 004 & 003 [Member] EBP 004 & 003. EBP 004 & 003 EBP, Investment, Plan Interest in Master Trust, Fair Value Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation Total investments at fair value in Savings Plans Master Trust for Alcoa USA Corporation Investment contracts at contract value Employee Benefit Plan Investments Maturity Year Employee Benefit Plan Investments Maturity Year. Maturity year Employee Benefit Plan Automatic Payroll Deductions Rate Employee benefit plan automatic payroll deductions rate. Employee benefit plan automatic payroll deductions rate EBP, Master Trust [Table Text Block] Schedule of Net Assets of Master Trust and Plans' Interest EBP 004 [Member] EBP 004. EBP 004 Hourly Plan Eligible Employees In Hourly Plan to Receive Cost-of-Living Contribution Of Per Hours Worked Eligible employees in hourly plan to receive cost-of-living contribution of per hours worked. Eligible employees in hourly plan to receive cost-of-living contribution of per hours worked Cover [Abstract] Asset held for investment EBP, Asset Held for Investment Asset held for investment EBP, Investment, Fair Value and NAV [Table] EBP, Schedule of Asset Held for Investment [Line Items] EBP, Investment, Fair Value and NAV [Line Items] EBP, Statement of Change in Net Asset Available for Benefit [Table] EBP, Subsequent Event [Abstract] Document Information [Line Items] EBP, Master Trust [Line Items]