Participant Loans, Cost EBP, Asset Held for Investment, Participant Loan, Cost EBP, Asset Held for Investment, Participant Loan, Cost Entity tax identification number Entity Tax Identification Number Participant rollover EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Rollover 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] Mutual fund investments Mutual Fund [Member] F.N.B. Corporation proceeds from sale of common stock EBP, Investment Sold, Excluding Plan Interest in Master Trust, Selling Price EBP, Related Party and Party-in-Interest Transactions [Table] EBP, Related Party and Party-in-Interest Transactions [Table] Pre-tax annual compensation contribution percentage 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 Measurements EBP, Investment, Fair Value and NAV [Text Block] Investments, at fair value: EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value Money market fund Money Market Funds [Member] Service period EBP, Requisite Service Period EBP, Requisite Service Period Level 1 Fair Value, Inputs, Level 1 [Member] Administrative expense EBP, Form 5500 Caption, Total Administrative Expenses EBP, Investment, Fair Value and NAV [Abstract] Summary of Parties-in-Interest Transactions EBP, Related Party and Party-in-Interest Transactions [Table Text Block] Statistical Measurement [Axis] Statistical Measurement [Axis] Additions: EBP, Change in Net Asset Available for Benefit, Increase [Abstract] EBP, Statement of Change in Net Asset Available for Benefit [Table] EBP, Statement of Change in Net Asset Available for Benefit [Table] Distributions to Participants EBP, Payment to Participant [Policy Text Block] EBP, Trustee EBP, Trustee [Member] Amendment Flag Amendment Flag EBP, Employer Contribution, Type [Domain] EBP, Employer Contribution, Type [Domain] EBP, Employer Contribution, Type [Domain] Basis of Presentation 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 EBP, Investment, Number of Shares EBP, Description of Plan and Accounting Change [Abstract] Receivables: EBP, Receivable [Abstract] EBP, Investment, Fair Value and NAV EBP, Investment, Fair Value and NAV [Table Text Block] Discretionary Performance-Based Contribution EBP, Discretionary Performance-Based Contribution [Member] EBP, Discretionary Performance-Based Contribution F.N.B. Corporation Common Stock Fund Common Stock [Member] Investments [Domain] Investments [Domain] Maximum vesting age EBP, Employer Contribution Maximum Vesting Age Maximum Vesting age of participant for company contribution and/ or investment earning in Company Matching Contributions, Fixed Rate Contributions, Discretionary Profit-Sharing Contributions, Qualified Non-Elective Contributions, and Disability Contributions. Use of Estimates EBP, Use of Estimate [Policy Text Block] EBP 002 EBP 002 [Member] EBP 002 EBP, Related Party and Party-in-Interest [Domain] EBP, Related Party and Party-in-Interest [Domain] Schedule H, Line 4i – Schedule of Assets (Held At End of Year) EBP, Schedule of Asset Held for Investment [Text Block] Cover [Abstract] Other EBP, Change in Net Asset Available for Benefit, Increase from Other EBP, Change in Net Asset Available for Benefit, Increase from Other Employer - cash EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash F.N.B. Corporation common stock shares purchased by the Plan EBP, Investment, Purchased, Number of Shares EBP, Forfeitures EBP, Forfeitures [Table Text Block] EBP, Forfeitures EBP, Related Party and Party-in-Interest [Axis] EBP, Related Party and Party-in-Interest [Axis] Minimum Minimum [Member] Notes receivable interest income EBP, Change in Net Asset Available for Benefit, Increase from Interest Income on Note Receivable from Participant Investment Type [Axis] Investment Type [Axis] Total contributions EBP, Change in Net Asset Available for Benefit, Increase from Contribution Participant EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Excluding Rollover Vesting percentage EBP, Employer Contribution Vesting Percentage Company contribution and/ or investment earning percentage vesting to the participant in Company Matching Contributions, Fixed Rate Contributions, Discretionary Profit-Sharing Contributions, Qualified Non-Elective Contributions, and Disability Contributions, upon completion of minimum service period or attainment of maximum vesting age Net appreciation (depreciation) in fair value of investments EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Gain (Loss) on Investment Dividend and interest income EBP, Change in Net Asset Available for Benefit, Increase from Interest and Dividend Income on Investment EBP, Description of Plan [Line Items] EBP, Description of Plan [Line Items] Plan number EBP, Plan Number Vesting period EBP, Employer Contribution Vesting Service Period Minimum Vesting service period for company contribution and/ or investment earning to the participant in Company Matching Contributions, Fixed Rate Contributions, Discretionary Profit-Sharing Contributions, Qualified Non-Elective Contributions, and Disability Contributions. EBP, Investment, Fair Value and NAV [Line Items] EBP, Investment, Fair Value and NAV [Line Items] Description of 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] In-kind shares of F.N.B. Corporation stock distributed EBP, Investment, Paid In Kind, Number of Shares EBP, Investment, Paid In Kind, Number of Shares EBP, Schedule of Asset Held for Investment [Line Items] EBP, Schedule of Asset Held for Investment [Line Items] Contributions EBP, Contribution [Policy Text Block] F.N.B. Corporation 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 EBP, Change in Net Asset Available for Benefit, Increase Investment, Identifier [Axis] Investment, Identifier [Axis] Administrative expenses EBP, Change in Net Asset Available for Benefit, Decrease from Administrative Expense Total EBP, Asset Held for Investment Risks and Uncertainties EBP, Risk and Uncertainty [Policy Text Block] Document Information [Line Items] Document Information [Line Items] Participant compensation match EBP, Employer Contribution, Participant Compensation Matched, Percentage EBP, Statement of Change in Net Asset Available for Benefit [Abstract] Level 2 Fair Value, Inputs, Level 2 [Member] F.N.B. Corporation common stock shares sold by the Plan EBP, Investment, Sold, Number of Shares Employer contributions EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash and Noncash EBP, Tax Status [Table] EBP, Tax Status [Table] Net increase (decrease) EBP, Change in Net Asset Available for Benefit, Increase (Decrease) Parties-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] Total receivables EBP, Receivable Employer contributions - cash EBP, Employer Contribution, Receivable Automatic deferral rate EBP, Participant Contribution, Automatic, Deferral Rate F.N.B. Corporation common stock dividends received EBP, Change in Net Asset Available for Benefit, Increase from Dividend Income on Investment Distributions to participants or beneficiaries EBP, Change in Net Asset Available for Benefit, Decrease from Payment to Participant Current value 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] EBP, Tax Status [Abstract] F.N.B. Corporation Common Stock Fund EBP, Employer, Common Stock Fund [Member] Cash EBP, Noninterest-Bearing Cash EBP, Employer Contribution, Type [Axis] EBP, Employer Contribution, Type [Axis] EBP, Employer Contribution, Type Administrative Expenses EBP, Expense [Policy Text Block] General loan, borrowing term EBP, Note Receivable From Participant, General Loan, Maximum Borrowing Term EBP, Note Receivable From Participant, General Loan, Maximum Borrowing Term Participant Loans EBP, Asset Held for Investment, Participant Loan, after Deemed Distribution Investment Valuation and Income Recognition EBP, Investment [Policy Text Block] Document Type Document Type Entity Central Index Key Entity Central Index Key Participant loan, interest rate EBP, Asset Held for Investment, Participant Loan, Interest Rate EBP, Tax Status [Line Items] EBP, Tax Status [Line Items] Deductions: EBP, Change in Net Asset Available for Benefit, Decrease [Abstract] Forfeitures used to reduce Corporation contributions EBP, Forfeited Nonvested Account, Decrease from Employer Contribution Notes receivable from participants EBP, Note Receivable from Participant Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Summary of Significant Accounting Policies EBP, Summary of Accounting Policy [Text Block] Entity Registrant Name Entity Registrant Name Basis spread on variable rate EBP, Participant Loan, Basis Spread On Variable Rate EBP, Participant Loan, Basis Spread On Variable Rate F.N.B. Corporation aggregate cost of purchased common stock EBP, Investment Acquired, Excluding Plan Interest in Master Trust, Cost Income Tax Status EBP, Tax Status [Text Block] Maximum borrowing, to total account, percentage EBP, Note Receivable from Participant, Account, Maximum Borrowing, to Total Account, Percentage Document Information [Table] Document Information [Table] Notes Receivable from Participants EBP, Note Receivable from Participant [Policy Text Block] Net investment income (loss) EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment Cash out limit EBP, Involuntary Cash-out Limit EBP, Involuntary Cash-out Limit EBP, Related Party and Party-in-Interest Transactions [Line Items] EBP, Related Party and Party-in-Interest Transactions [Line Items] Level 3 Fair Value, Inputs, Level 3 [Member] Net assets available for benefits Beginning of year End of year EBP, Net Asset Available for Benefit Entity [Domain] Entity [Domain] Contributions: EBP, Change in Net Asset Available for Benefit, Increase from Contribution [Abstract] Forfeiture balance at end of year EBP, Forfeited Nonvested Account Employer contribution match EBP, Employer Contribution, Matching Percentage EBP, Investment, Fair Value and NAV [Table] EBP, Investment, Fair Value and NAV [Table] EBP, Statement of Net Asset Available for Benefit [Line Items] EBP, Statement of Net Asset Available for Benefit [Line Items]