Entity tax identification number Entity Tax Identification Number Rollovers EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Rollover Total investments at fair value Total investments at fair value EBP, Investment, Fair Value Maximum Maximum [Member] Legal Entity [Axis] Legal Entity [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] EBP, Description of Plan [Table] EBP, Description of Plan [Table] Investments, Measured At Fair Value Investments, Measured At Fair Value [Member] Investments, Measured At Fair Value Employer contribution vesting service period maximum EBP, Employer Contribution Vesting Service Period Maximum EBP, Employer Contribution Vesting Service Period Maximum EBP, Related Party and Party-in-Interest Transactions [Table] EBP, Related Party and Party-in-Interest Transactions [Table] Maximum annual compensation EBP, Participant Contribution, Pretax, Maximum Annual Compensation to Total Compensation, Percentage Total deductions EBP, Change in Net Asset Available for Benefit, Decrease Maximum borrowing, amount EBP, Note Receivable from Participant, Account, Maximum Borrowing, Amount Fair Value Measurement EBP, Investment, Fair Value and NAV [Text Block] Minimum borrowing EBP, Note Receivable from Participant, Account, Minimum Borrowing, Amount General loan maximum borrowing term EBP, Note Receivable From Participant, General Loan, Maximum Borrowing Term EBP, Note Receivable From Participant, General Loan, Maximum Borrowing Term Investment income from investments EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Investment Income (Loss), after Investment Expense Interest in registered investment companies EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value Percent in constant duration contracts EBP, Participant Contributions, Product Allocation, Percent In Constant Duration Contracts EBP, Participant Contributions, Product Allocation, Percent In Constant Duration Contracts Plan's Interest in Master Trust Balances EBP, Nonconsolidated, Plan Interest in Master Trust [Member] Level 1 Fair Value, Inputs, Level 1 [Member] Corporate common stock Corporate Debt Securities [Member] EBP, Investment, Fair Value and NAV [Abstract] Statistical Measurement [Axis] Statistical Measurement [Axis] EBP, Statement of Change in Net Asset Available for Benefit [Table] EBP, Statement of Change in Net Asset Available for Benefit [Table] Joint venture ownership percentage EBP, Joint Venture, Ownership Percentage EBP, Joint Venture, Ownership Percentage Payment of Benefits EBP, Payment to Participant [Policy Text Block] Net assets transferred from plan, net EBP, Change in Net Asset Available for Benefit, Transfer to (from) Plan Unfunded commitments EBP, Fair Value, Investment, NAV, Unfunded Commitment EBP, Master Trust [Line Items] EBP, Master Trust [Line Items] Amendment Flag Amendment Flag Basis of Accounting EBP, Basis of Accounting [Policy Text Block] EBP, Schedule of Asset Held for Investment [Table] EBP, Schedule of Asset Held for Investment [Table] Number of shares (in shares) EBP, Investment, Number of Shares EBP, Description of Plan and Accounting Change [Abstract] EBP, Investment, Fair Value and NAV EBP, Investment, Fair Value and NAV [Table Text Block] EBP 005 EBP 005 [Member] EBP 005 Investments [Domain] Investments [Domain] EBP, Master Trust [Abstract] Interest in Allegheny Technologies Incorporated Master Trust EBP, Investment, Plan Interest in Master Trust, Contract Value Percent in cash EBP, Participant Contributions, Product Allocation, Percent In Cash EBP, Participant Contributions, Product Allocation, Percent In Cash Use of Estimates EBP, Use of Estimate [Policy Text Block] Pooled separate accounts EBP, Pooled Separate Account [Member] Schedule H, Line 4i – Schedule of Assets (Held At End of Year) EBP, Schedule of Asset Held for Investment [Text Block] Cover [Abstract] Risks and Uncertainties EBP, Risk and Uncertainty [Text Block] Employer EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash Synthetic investment contracts EBP, Synthetic Investment Contract [Member] Minimum Minimum [Member] Investment Type [Axis] Investment Type [Axis] Interest income on notes receivable from participants EBP, Change in Net Asset Available for Benefit, Increase from Interest Income on Note Receivable from Participant Total contributions EBP, Change in Net Asset Available for Benefit, Increase from Contribution Employee EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Excluding Rollover Net appreciation in fair value of investments EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Gain (Loss) on Investment EBP, Description of Plan [Line Items] EBP, Description of Plan [Line Items] Plan number EBP, Plan Number EBP, Investment, Fair Value and NAV [Line Items] EBP, Investment, Fair Value and NAV [Line Items] Description of the Plan EBP, Description of Plan [Text Block] EBP, Statement of Change in Net Asset Available for Benefit [Line Items] EBP, Statement of Change in Net Asset Available for Benefit [Line Items] EBP, Statement of Net Asset Available for Benefit [Table] EBP, Statement of Net Asset Available for Benefit [Table] EBP, Schedule of Asset Held for Investment [Line Items] EBP, Schedule of Asset Held for Investment [Line Items] Net income from interest in registered investment companies EBP, Change in Net Asset Available for Benefit, Increase from Interest Income on Investment EBP, Nonconsolidated, Master Trust and Plan Interest in Master Trust [Domain] EBP, Nonconsolidated, Master Trust and Plan Interest in Master Trust [Domain] Corporate common stock EBP, Employer, Common Stock [Member] EBP, Schedule of Asset Held for Investment [Abstract] EBP, Accounting Policy [Table] EBP, Accounting Policy [Table] Total additions to net assets EBP, Change in Net Asset Available for Benefit, Increase Cash Cash [Member] Fees Administrative expenses and other, net EBP, Change in Net Asset Available for Benefit, Decrease from Administrative Expense Plan Transfers EBP, Plan Transfers [Policy Text Block] EBP, Plan Transfers Total investments at contract value Total investments at contract value EBP, Investment, Contract Value Net increase in net assets available for benefits EBP, Change In Net Asset Available For Benefit, Increase (Decrease), After Transfers EBP, Change In Net Asset Available For Benefit, Increase (Decrease), After Transfers Document Information [Line Items] Document Information [Line Items] EBP, Risk and Uncertainty [Line Items] EBP, Risk and Uncertainty [Line Items] EBP, Risk and Uncertainty [Table] EBP, Risk and Uncertainty [Table] Investments EBP, Master Trust [Text Block] EBP, Statement of Change in Net Asset Available for Benefit [Abstract] Primary residence, maximum borrowing term EBP, Note Receivable From Participant, Account, Primary Residence, Maximum Borrowing Term EBP, Note Receivable From Participant, Account, Primary Residence, Maximum Borrowing Term EBP, Tax Status [Table] EBP, Tax Status [Table] Net increase in net assets available for benefits prior to net assets transferred out EBP, Change in Net Asset Available for Benefit, Increase (Decrease) Party-In-Interest Transactions EBP, Related Party and Party-in-Interest Transactions [Text Block] EBP, Related Party and Party-in-Interest Transactions [Abstract] EBP, Accounting Policy, Accounting Standard Update, and Change in Accounting Principle [Abstract] Net appreciation in fair value of investments EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Unrealized Gain (Loss) on Investment Investments at fair value: EBP, Investment, Fair Value [Abstract] Benefits paid to participants EBP, Change in Net Asset Available for Benefit, Decrease from Payment to Participant Interest in Allegheny Technologies Incorporated Master Trust EBP, Investment, Plan Interest in Master Trust, Fair Value Registered investment companies - Self-directed accounts EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Current Value Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] EBP, Statement of Net Asset Available for Benefit [Abstract] EBP, Accounting Policy [Line Items] EBP, Accounting Policy [Line Items] Max number of loans per participant EBP, Max Number Of Loans Per Participant EBP, Max Number Of Loans Per Participant Investments at contract value: EBP, Investment, Contract Value [Abstract] EBP, Tax Status [Abstract] Net investment income from Plan interest in Allegheny Technologies Incorporated Master Trust EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Change in Plan Interest in Master Trust Participant loans* (4.25% to 9.50%, with maturities through 2040) EBP, Asset Held for Investment, Participant Loan, after Deemed Distribution Investment Valuation EBP, Investment [Policy Text Block] EBP, Master Trust [Table] EBP, Master Trust [Table] Document Type Document Type Plan Termination EBP, Plan Termination [Text Block] Entity Central Index Key Entity Central Index Key Interest rate EBP, Asset Held for Investment, Participant Loan, Interest Rate Common collective trusts Common Collective Trust [Member] EBP, Risk and Uncertainty [Abstract] EBP, Tax Status [Line Items] EBP, Tax Status [Line Items] Notes receivable from participants EBP, Note Receivable from Participant Master Trust Balances EBP, Nonconsolidated, Master Trust [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Significant Accounting Policies EBP, Summary of Accounting Policy [Text Block] Entity Registrant Name Entity Registrant Name Schedule of Master Trust Net Assets EBP, Master Trust [Table Text Block] Registered investment companies Other Investment Companies [Member] Income Tax Status EBP, Tax Status [Text Block] Maximum borrowing, percentage EBP, Note Receivable from Participant, Account, Maximum Borrowing, to Total Account, Percentage Document Information [Table] Document Information [Table] Investments, Measured At Contract Value Investments, Measured At Contract Value [Member] Investments, Measured At Contract Value Notes Receivable from Participants EBP, Note Receivable from Participant [Policy Text Block] Total investment income EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment EBP, Nonconsolidated, Master Trust and Plan Interest in Master Trust [Axis] EBP, Nonconsolidated, Master Trust and Plan Interest in Master Trust [Axis] EBP, Related Party and Party-in-Interest Transactions [Line Items] EBP, Related Party and Party-in-Interest Transactions [Line Items] Net assets available for benefits Net assets available for benefits at beginning of year Net assets available for benefits at end of year EBP, Net Asset Available for Benefit Entity [Domain] Entity [Domain] NAV (a) Fair Value Measured at Net Asset Value Per Share [Member] Percent in fixed maturity contracts EBP, Participant Contributions, Product Allocation, Percent In Fixed Maturity Contracts EBP, Participant Contributions, Product Allocation, Percent In Fixed Maturity Contracts EBP, Investment, Fair Value and NAV [Table] EBP, Investment, Fair Value and NAV [Table] Plan's interest in master trust EBP, Interest in Master Trust, Percentage EBP, Statement of Net Asset Available for Benefit [Line Items] EBP, Statement of Net Asset Available for Benefit [Line Items]