SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
Sep. 30, 2018
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation Our accompanying Consolidated Financial Statements and these Notes to the Financial Statements include subsidiaries in which we have a controlling financial interest. We own and operate FNBPA, First National Trust Company, First National Investment Services Company, LLC, F.N.B. Investment Advisors, Inc., First National Insurance Agency, LLC, Bank Capital Services, LLC and F.N.B. Capital Corporation, LLC, and include results for each of these entities in the accompanying Consolidated Financial Statements. The accompanying Consolidated Financial Statements include all adjustments that are necessary, in the opinion of management, to fairly reflect our financial position and results of operations in accordance with U.S. generally accepted accounting principles. All significant intercompany balances and transactions have been eliminated. Certain prior period amounts have been reclassified to conform to the current period presentation. Such reclassifications had no impact on our net income and stockholders’ equity. Events occurring subsequent to the date of the September 30, 2018 Balance Sheet have been evaluated for potential recognition or disclosure in the Consolidated Financial Statements through the date of the filing of the Consolidated Financial Statements with the Securities and Exchange Commission. Certain information and Note disclosures normally included in Consolidated Financial Statements prepared in accordance with GAAP have been condensed or omitted pursuant to the rules and regulations of the SEC. The interim operating results are not necessarily indicative of operating results FNB expects for the full year. These interim unaudited Consolidated Financial Statements should be read in conjunction with the audited Consolidated Financial Statements and Notes thereto included in FNB’s 2017 Annual Report on Form 10-K filed with the SEC on February 28, 2018. For a detailed description of our significant accounting policies, see Note 1 "Summary of Significant Accounting Policies" in the 2017 Form 10-K. The accounting policies presented below have been added or amended for newly material items or the adoption of new accounting standards. Use of Estimates Our accounting and reporting policies conform with GAAP. The preparation of Financial Statements in conformity with GAAP requires us to make estimates and assumptions that affect the amounts reported in the Consolidated Financial Statements and accompanying Notes. Actual results could materially differ from those estimates. Material estimates that are particularly susceptible to significant changes include the allowance for credit losses, accounting for acquired loans, fair value of financial instruments, goodwill and other intangible assets, income taxes and deferred tax assets and litigation. Revenue from Contracts with Customers We earn certain revenues from contracts with customers. These revenues are recognized when control of the promised services is transferred to the customers in an amount that reflects the consideration we expect to be entitled to in an exchange for those services. In determining the appropriate revenue recognition for our contracts with customers, we consider whether the contract has commercial substance and is approved by both parties with identifiable contractual rights, payment terms, and the collectability of consideration is probable. Generally, we satisfy our performance obligations upon the completion of services at the amount to which we have the right to invoice or charge under contracts with an original expected duration of one year or less. We apply this guidance on a portfolio basis to contracts with similar characteristics and for which we believe the results would not differ materially from applying this guidance to individual contracts. Our services provided under contracts with customers are transferred at the point in time when the services are rendered. Generally, we do not defer incremental direct costs to obtain contracts with customers that would be amortized in one year or less under the practical expedient. These costs are recognized as expense, primarily salary and benefit expense, in the period incurred. Deposit Services. We recognize revenue on deposit services based on published fees for services provided. Demand and savings deposit customers have the right to cancel their depository arrangements and withdraw their deposited funds at any time without prior notice. When services involve deposited funds that can be retrieved by customers without penalties, we consider the service contract term to be day-to-day, where each day represents the renewal of the contract. The contract does not extend beyond the services performed and revenue is recognized at the end of the contract term (daily) as the performance obligation is satisfied. No deposit services fees exist for long-term deposit products beyond early withdrawal penalties, which are earned on these products at the time of early termination. Revenue from deposit services fees are reduced where we have a history of waived or reduced fees by customer request or due to a customer service issue, by historical experience, or another acceptable method in the same period as the related revenues. Revenues from deposit services are reported in the Consolidated Statements of Income as service charges and in the Community Banking segment as non-interest income. Wealth Management Services. Wealth advisory and trust services are provided on a month-to-month basis and invoiced as services are rendered. Fees are based on a fixed amount or a scale based on the level of services provided or assets under management. The customer has the right to terminate their services agreement at any time. We determine the value of services performed based on the fee schedule in effect at the time the services are performed. Revenues from wealth advisory and trust services are reported in the Consolidated Statements of Income as trust services and securities commissions and fees, and in the Wealth segment as non-interest income. Insurance Services. Insurance services include full-service insurance brokerage services offering numerous lines of commercial and personal insurance through major carriers to businesses and individuals within our geographic markets. We recognize revenue on insurance contracts in effect based on contractually specified commission payments on premiums that are paid by the customer to the insurance carrier. Contracts are cancellable at any time and we have no performance obligation to the customers beyond the time the insurance is placed into effect. Revenues from insurance services are reported in the Consolidated Statements of Income as insurance commissions and fees, and in the Insurance segment as non-interest income. Debt Securities Debt securities comprise a significant portion of our Consolidated Balance Sheets. Such securities can be classified as trading, HTM or AFS. As of September 30, 2018 and 2017, we did not hold any trading debt securities. Debt securities HTM are the securities that management has the positive intent and ability to hold until their maturity. Such securities are carried at cost, adjusted for related amortization of premiums and accretion of discounts through interest income from securities, and subject to evaluation for OTTI. Debt securities that are not classified as trading or HTM are classified as AFS. Such securities are carried at fair value with net unrealized gains and losses deemed to be temporary and OTTI attributable to non-credit factors reported separately as a component of other comprehensive income, net of tax. We evaluate our debt securities in a loss position for OTTI on a quarterly basis at the individual security level based on our intent to sell. If we intend to sell the debt security or it is more likely than not we will be required to sell the security before recovery of its amortized cost basis, OTTI must be recognized in earnings equal to the entire difference between the investments’ amortized cost basis and its fair value. If we do not intend to sell the debt security and it is not more likely than not that we will be required to sell the security before recovery of its amortized cost basis, OTTI must be separated into the amount representing credit loss and the amount related to all other market factors. The amount related to credit loss will be recognized in earnings. The amount related to other market factors will be recognized in other comprehensive income, net of applicable taxes. We perform our OTTI evaluation process in a consistent and systematic manner and include an evaluation of all available evidence. This process considers factors such as length of time and anticipated recovery period of the impairment, recent events specific to the issuer and recent experience regarding principal and interest payments. Low Income Housing Tax Credit (LIHTC) Partnerships We invest in various affordable housing projects that qualify for LIHTCs. The net investments are recorded in other assets on the Consolidated Balance Sheets. These investments generate a return through the realization of federal tax credits. We use the proportional amortization method to account for a majority of our investments in these entities. LIHTCs that do not meet the requirements of the proportional amortization method are recognized using the equity method. Our net investment in LIHTCs was $35.7 million and $20.9 million at September 30, 2018 and December 31, 2017, respectively. Our unfunded commitments in LIHTCs were $46.6 million and $67.2 million at September 30, 2018 and December 31, 2017, respectively. Cloud Computing Arrangements We evaluate fees paid for cloud computing arrangements to determine if those arrangements include the purchase of or license to use software that should be accounted for separately as internal-use software. If a contract includes the purchase or license to use software that should be accounted for separately as internal-use software, the contract is amortized over the software’s identified useful life in amortization of intangibles. For contracts that do not include a software license, the contract is accounted for as a service contract with fees paid recorded in other non-interest expense. In the third quarter of 2018, we early adopted, on a prospective basis, ASU 2018-15 (See Note 2) which allows for implementation costs for activities performed in cloud computing arrangements that are a service contract to be accounted for under the internal-use software guidance which allows for certain implementation costs to be capitalized depending on the nature of the costs and the project stage. Prior to the adoption of ASU 2018-15 all implementation costs for cloud computing arrangements that were a service contract were expensed as incurred.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Basis of Presentation

Our accompanying Consolidated Financial Statements and these Notes to the Financial Statements include subsidiaries in which we have a controlling financial interest. We own and operate FNBPA, First National Trust Company, First National Investment Services Company, LLC, F.N.B. Investment Advisors, Inc., First National Insurance Agency, LLC, Bank Capital Services, LLC and F.N.B. Capital Corporation, LLC, and include results for each of these entities in the accompanying Consolidated Financial Statements.

The accompanying Consolidated Financial Statements include all adjustments that are necessary, in the opinion of management, to fairly reflect our financial position and results of operations in accordance with U.S. generally accepted accounting principles. All significant intercompany balances and transactions have been eliminated. Certain prior period amounts have been reclassified to conform to the current period presentation. Such reclassifications had no impact on our net income and stockholders’ equity. Events occurring subsequent to the date of the September 30, 2018 Balance Sheet have been evaluated for potential recognition or disclosure in the Consolidated Financial Statements through the date of the filing of the Consolidated Financial Statements with the Securities and Exchange Commission.

Certain information and Note disclosures normally included in Consolidated Financial Statements prepared in accordance with GAAP have been condensed or omitted pursuant to the rules and regulations of the SEC. The interim operating results are not necessarily indicative of operating results FNB expects for the full year. These interim unaudited Consolidated Financial Statements should be read in conjunction with the audited Consolidated Financial Statements and Notes thereto included in FNB’s 2017 Annual Report on Form 10-K filed with the SEC on February 28, 2018. For a detailed description of our significant accounting policies, see Note 1 "Summary of Significant Accounting Policies" in the 2017 Form 10-K. The accounting policies presented below have been added or amended for newly material items or the adoption of new accounting standards.

Use of Estimates

Our accounting and reporting policies conform with GAAP. The preparation of Financial Statements in conformity with GAAP requires us to make estimates and assumptions that affect the amounts reported in the Consolidated Financial Statements and accompanying Notes. Actual results could materially differ from those estimates. Material estimates that are particularly susceptible to significant changes include the allowance for credit losses, accounting for acquired loans, fair value of financial instruments, goodwill and other intangible assets, income taxes and deferred tax assets and litigation.

Revenue from Contracts with Customers

We earn certain revenues from contracts with customers. These revenues are recognized when control of the promised services is transferred to the customers in an amount that reflects the consideration we expect to be entitled to in an exchange for those services.

In determining the appropriate revenue recognition for our contracts with customers, we consider whether the contract has commercial substance and is approved by both parties with identifiable contractual rights, payment terms, and the collectability of consideration is probable. Generally, we satisfy our performance obligations upon the completion of services at the amount to which we have the right to invoice or charge under contracts with an original expected duration of one year or less. We apply this guidance on a portfolio basis to contracts with similar characteristics and for which we believe the results would not differ materially from applying this guidance to individual contracts.

Our services provided under contracts with customers are transferred at the point in time when the services are rendered. Generally, we do not defer incremental direct costs to obtain contracts with customers that would be amortized in one year or less under the practical expedient. These costs are recognized as expense, primarily salary and benefit expense, in the period incurred.

Deposit Services. We recognize revenue on deposit services based on published fees for services provided. Demand and savings deposit customers have the right to cancel their depository arrangements and withdraw their deposited funds at any time without prior notice. When services involve deposited funds that can be retrieved by customers without penalties, we consider the service contract term to be day-to-day, where each day represents the renewal of the contract. The contract does not extend beyond the services performed and revenue is recognized at the end of the contract term (daily) as the performance obligation is satisfied.

No deposit services fees exist for long-term deposit products beyond early withdrawal penalties, which are earned on these products at the time of early termination.

Revenue from deposit services fees are reduced where we have a history of waived or reduced fees by customer request or due to a customer service issue, by historical experience, or another acceptable method in the same period as the related revenues. Revenues from deposit services are reported in the Consolidated Statements of Income as service charges and in the Community Banking segment as non-interest income.

Wealth Management Services. Wealth advisory and trust services are provided on a month-to-month basis and invoiced as services are rendered. Fees are based on a fixed amount or a scale based on the level of services provided or assets under management. The customer has the right to terminate their services agreement at any time. We determine the value of services performed based on the fee schedule in effect at the time the services are performed. Revenues from wealth advisory and trust services are reported in the Consolidated Statements of Income as trust services and securities commissions and fees, and in the Wealth segment as non-interest income.

Insurance Services. Insurance services include full-service insurance brokerage services offering numerous lines of commercial and personal insurance through major carriers to businesses and individuals within our geographic markets. We recognize revenue on insurance contracts in effect based on contractually specified commission payments on premiums that are paid by the customer to the insurance carrier. Contracts are cancellable at any time and we have no performance obligation to the customers beyond the time the insurance is placed into effect. Revenues from insurance services are reported in the Consolidated Statements of Income as insurance commissions and fees, and in the Insurance segment as non-interest income.

Debt Securities

Debt securities comprise a significant portion of our Consolidated Balance Sheets. Such securities can be classified as trading, HTM or AFS. As of September 30, 2018 and 2017, we did not hold any trading debt securities.

Debt securities HTM are the securities that management has the positive intent and ability to hold until their maturity. Such securities are carried at cost, adjusted for related amortization of premiums and accretion of discounts through interest income from securities, and subject to evaluation for OTTI.

Debt securities that are not classified as trading or HTM are classified as AFS. Such securities are carried at fair value with net unrealized gains and losses deemed to be temporary and OTTI attributable to non-credit factors reported separately as a component of other comprehensive income, net of tax.

We evaluate our debt securities in a loss position for OTTI on a quarterly basis at the individual security level based on our intent to sell. If we intend to sell the debt security or it is more likely than not we will be required to sell the security before recovery of its amortized cost basis, OTTI must be recognized in earnings equal to the entire difference between the investments’ amortized cost basis and its fair value. If we do not intend to sell the debt security and it is not more likely than not that we will be required to sell the security before recovery of its amortized cost basis, OTTI must be separated into the amount representing credit loss and the amount related to all other market factors. The amount related to credit loss will be recognized in earnings. The amount related to other market factors will be recognized in other comprehensive income, net of applicable taxes.

We perform our OTTI evaluation process in a consistent and systematic manner and include an evaluation of all available evidence. This process considers factors such as length of time and anticipated recovery period of the impairment, recent events specific to the issuer and recent experience regarding principal and interest payments.

Low Income Housing Tax Credit (LIHTC) Partnerships

We invest in various affordable housing projects that qualify for LIHTCs. The net investments are recorded in other assets on the Consolidated Balance Sheets. These investments generate a return through the realization of federal tax credits. We use the proportional amortization method to account for a majority of our investments in these entities. LIHTCs that do not meet the requirements of the proportional amortization method are recognized using the equity method. Our net investment in LIHTCs was $35.7 million and $20.9 million at September 30, 2018 and December 31, 2017, respectively. Our unfunded commitments in LIHTCs were $46.6 million and $67.2 million at September 30, 2018 and December 31, 2017, respectively.

Cloud Computing Arrangements

We evaluate fees paid for cloud computing arrangements to determine if those arrangements include the purchase of or license to use software that should be accounted for separately as internal-use software. If a contract includes the purchase or license to use software that should be accounted for separately as internal-use software, the contract is amortized over the software’s identified useful life in amortization of intangibles. For contracts that do not include a software license, the contract is accounted for as a service contract with fees paid recorded in other non-interest expense.

In the third quarter of 2018, we early adopted, on a prospective basis, ASU 2018-15 (See Note 2) which allows for implementation costs for activities performed in cloud computing arrangements that are a service contract to be accounted for under the internal-use software guidance which allows for certain implementation costs to be capitalized depending on the nature of the costs and the project stage. Prior to the adoption of ASU 2018-15 all implementation costs for cloud computing arrangements that were a service contract were expensed as incurred.