Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2018
Summary of Signficant Accounting Policies
Nature of Business Policy	NOTE 1: SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Nature of Business Auburn National Bancorporation, Inc. (the “Company”) is a bank holding company whose primary business is conducted by its wholly-owned subsidiary, AuburnBank (the “Bank”). AuburnBank is a commercial bank located in Auburn, Alabama. The Bank provides a full range of banking services in its primary market area, Lee County, which includes the Auburn-Opelika Metropolitan Statistical Area.
Basis of Presentation Policy	Basis of Presentation The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. Auburn National Bancorporation Capital Trust I was an affiliate of the Company and was included in these consolidated financial statements pursuant to the equity method of accounting. On April 27, 2018, the Trust was dissolved. Significant intercompany transactions and accounts are eliminated in consolidation.
Use of Estimates Policy	Use of Estimates The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities as of the balance sheet date and the reported amounts of income and expense during the reporting period. Actual results could differ from those estimates. Material estimates that are particularly susceptible to significant change in the near term include the determination of the allowance for loan losses, fair value measurements, valuation of other real estate owned, and valuation of deferred tax assets.
Accounting Standards Adopted in 2014	Accounting Standards Adopted in 2018 In 2018, the Company adopted new guidance related to the following Accounting Standards Update (“Update” or “ASU”): ASU 2014-09, Revenue from Contracts with Customers; ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities; ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments; and ASU 2016-18, Restricted Cash. Information about these pronouncements is described in more detail below. ASU 2014-09, Revenue from Contracts with Customers (Topic 606), was developed as a joint project with the International Accounting Standards Board to remove inconsistencies in revenue requirements and provide a more robust framework for addressing revenue issues. The ASU’s core principle is that an entity should recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which an entity expects to be entitled in exchange for those goods or services. In August 2015, the FASB issued ASU 2015-14, which deferred the effective date by one year (i.e., interim and annual reporting periods beginning after December 15, 2017). Early adoption was permitted, but not before the original effective date (i.e., interim and annual reporting periods beginning after December 15, 2016). The ASU may be adopted using either a modified retrospective method or a full retrospective method. The Company adopted the ASU during the first quarter of 2018, as required, using a modified retrospective approach. The majority of the Company’s revenue stream is generated from interest income on loans and deposits, which are outside the scope of Topic 606. The Company’s sources of income that fall within the scope of Topic 606 include service charges on deposits, investment services, interchange fees and gains and losses on sales of other real estate, all of which are presented as components of noninterest income. The Company has evaluated the effect of Topic 606 on these fee-based income streams and concluded that adoption of the standard did not materially impact its financial statements. The following is a summary of the implementation considerations for the revenue streams that fall within the scope of Topic 606: Service charges on deposits, investment services, ATM and interchange fees – Fees from these services are either transaction-based, for which the performance obligations are satisfied when the individual transaction is processed, or set periodic service charges, for which the performance obligations are satisfied over the period the service is provided. Transaction-based fees are recognized at the time the transaction is processed, and periodic service charges are recognized over the service period. The adoption of Topic 606 had no impact on the Company’s revenue recognition practice for these services. Gains on sales of other real estate – ASU 2014-09 creates Topic 610-20, under which a gain on sale should be recognized when a contract for sale exists and control of the asset has been transferred to the buyer. Topic 606 lists several criteria required to conclude that a contract for sale exists, including a determination that the institution will collect substantially all of the consideration to which it is entitled. This presents a key difference between the prior and new guidance related to the recognition of the gain when the institution finances the sale of the property. Rather than basing recognition on the amount of the buyer’s initial investment, which was the primary consideration under prior guidance, the analysis is now based on various factors including not only the loan to value, but also the credit quality of the borrower, the structure of the loan, and any other factors that may affect collectability. While these differences may affect the decision to recognize or defer gains on sales of other real estate in circumstances where the Company has financed the sale, the effects would not be material to its consolidated financial statements. ASU 2016-01, Financial Instruments – Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities, enhances the reporting model for financial instruments to provide users of financial statements with more decision-useful information. The ASU addresses certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. Some of the amendments include the following: (1) Require equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income; (2) Simplify the impairment assessment of equity investments without readily determinable fair values by requiring a qualitative assessment to identify impairment; (3) Require public business entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes; (4) Require an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value; among others. For public business entities, the amendments of this ASU are effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The adoption of this ASU on January 1, 2018 did not have a material impact on the Company’s Consolidated Financial Statements. In accordance with (3) above, the Company measured the fair value of its loan portfolio as of December 31, 2018 using an exit price notion and will continue to do so going forward. See Note 16, Fair Value. ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments, provides guidance on eight specific cash flow issues where current GAAP is either unclear or does not include specific guidance on classification in the statement of cash flows. The new guidance is effective for annual and interim reporting periods in fiscal years beginning after December 15, 2017. The Company adopted ASU No. 2016-15 on January 1, 2018. ASU No. 2016-15 did not have a material impact on the Company’s Consolidated Financial Statements. ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash, amends guidance on how the statement of cash flows presents the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Under the new guidance, amounts generally described as restricted cash and restricted cash equivalents are included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The amendments in this Update do not provide a definition of restricted cash or restricted cash equivalents. The new guidance is effective for public business entities for annual and interim reporting periods in fiscal years beginning after December 15, 2017. The Company adopted ASU No. 2016-18 on January 1, 2018. ASU No. 2016-18 did not have a material impact on the Company’s Consolidated Financial Statements.
Cash Equivalents Policy	Cash Equivalents Cash equivalents include cash on hand, cash items in process of collection, amounts due from banks, including interest bearing deposits with other banks, and federal funds sold.
Marketable Securities, Policy	For the securities in the previous table, the Company does not have the intent to sell and has determined it is not more likely than not that the Company will be required to sell the security before recovery of the amortized cost basis, which may be maturity. On a quarterly basis, the Company assesses each security for credit impairment. For debt securities, the Company evaluates, where necessary, whether credit impairment exists by comparing the present value of the expected cash flows to the securities’ amortized cost basis. In determining whether a loss is temporary, the Company considers all relevant information including: the length of time and the extent to which the fair value has been less than the amortized cost basis; adverse conditions specifically related to the security, an industry, or a geographic area (for example, changes in the financial condition of the issuer of the security, or in the case of an asset-backed debt security, in the financial condition of the underlying loan obligors, including changes in technology or the discontinuance of a segment of the business that may affect the future earnings potential of the issuer or underlying loan obligors of the security or changes in the quality of the credit enhancement); the historical and implied volatility of the fair value of the security; the payment structure of the debt security and the likelihood of the issuer being able to make payments that increase in the future; failure of the issuer of the security to make scheduled interest or principal payments; any changes to the rating of the security by a rating agency; and recoveries or additional declines in fair value subsequent to the balance sheet date. Agency obligations The unrealized losses associated with agency obligations were primarily driven by changes in interest rates and not due to the credit quality of the securities. These securities were issued by U.S. government agencies or government-sponsored entities and did not have any credit losses given the explicit government guarantee or other government support. Agency residential mortgage-backed securities (“RMBS”) The unrealized losses associated with agency RMBS were primarily driven by changes in interest rates and not due to the credit quality of the securities. These securities were issued by U.S. government agencies or government-sponsored entities and did not have any credit losses given the explicit government guarantee or other government support. Securities of U.S. states and political subdivisions The unrealized losses associated with securities of U.S. states and political subdivisions were primarily driven by changes in interest rates and were not due to the credit quality of the securities. Some of these securities are guaranteed by a bond insurer, but management did not rely on the guarantee in making its investment decision. These securities will continue to be monitored as part of the Company’s quarterly impairment analysis, but are expected to perform even if the rating agencies reduce the credit rating of the bond insurers. As a result, the Company expects to recover the entire amortized cost basis of these securities. The carrying values of the Company’s investment securities could decline in the future if the financial condition of an issuer deteriorates and the Company determines it is probable that it will not recover the entire amortized cost basis for the security. As a result, there is a risk that other-than-temporary impairment charges may occur in the future.
Loans Held for Sale Policy	Loans held for sale Loans originated and intended for sale in the secondary market are carried at the lower of cost or estimated fair value in the aggregate. Loan sales are recognized when the transaction closes, the proceeds are collected, and ownership is transferred. Continuing involvement, through the sales agreement, consists of the right to service the loan for a fee for the life of the loan, if applicable. Gains on the sale of loans held for sale are recorded net of related costs, such as commissions, and reflected as a component of mortgage lending income in the consolidated statements of earnings. In the course of conducting the Bank’s mortgage lending activities of originating mortgage loans and selling those loans in the secondary market, the Bank makes various representations and warranties to the purchaser of the mortgage loans. Every loan closed by the Bank’s mortgage center is run through a government agency automated underwriting system. Any exceptions noted during this process are remedied prior to sale. These representations and warranties also apply to underwriting the real estate appraisal opinion of value for the collateral securing these loans. Failure by the Company to comply with the underwriting and/or appraisal standards could result in the Company being required to repurchase the mortgage loan or to reimburse the investor for losses incurred (make whole requests) if such failure cannot be cured by the Company within the specified period following discovery.
Loans Policy	Loans Loans are reported at their outstanding principal balances, net of any unearned income, charge-offs, and any deferred fees or costs on originated loans. Interest income is accrued based on the principal balance outstanding.
Loans, Origination Fees Policy	Loan origination fees, net of certain loan origination costs, are deferred and recognized in interest income over the contractual life of the loan using the effective interest method. Loan commitment fees are generally deferred and amortized on a straight-line basis over the commitment period, which results in a recorded amount that approximates fair value.
Loans, Nonacrrual Policy	The accrual of interest on loans is discontinued when there is a significant deterioration in the financial condition of the borrower and full repayment of principal and interest is not expected or the principal or interest is more than 90 days past due, unless the loan is both well-collateralized and in the process of collection. Generally, all interest accrued but not collected for loans that are placed on nonaccrual status is reversed against current interest income. Interest collections on nonaccrual loans are generally applied as principal reductions. The Company determines past due or delinquency status of a loan based on contractual payment terms.
Loans, Impaired Policy	A loan is considered impaired when it is probable the Company will be unable to collect all principal and interest payments due according to the contractual terms of the loan agreement. Individually identified impaired loans are measured based on the present value of expected payments using the loan’s original effective rate as the discount rate, the loan’s observable market price, or the fair value of the collateral if the loan is collateral dependent. If the recorded investment in the impaired loan exceeds the measure of fair value, a valuation allowance may be established as part of the allowance for loan losses. Changes to the valuation allowance are recorded as a component of the provision for loan losses.
Loans, Troubled Debt Restructuring Policy	Impaired loans also include troubled debt restructurings (“TDRs”). In the normal course of business, management may grant concessions to borrowers who are experiencing financial difficulty. The concessions granted most frequently for TDRs involve reductions or delays in required payments of principal and interest for a specified time, the rescheduling of payments in accordance with a bankruptcy plan or the charge-off of a portion of the loan. In most cases, the conditions of the credit also warrant nonaccrual status, even after the restructuring occurs. As part of the credit approval process, the restructured loans are evaluated for adequate collateral protection in determining the appropriate accrual status at the time of restructuring. TDR loans may be returned to accrual status if there has been at least a six-month sustained period of repayment performance by the borrower.
Allowance for Loan Losses Policy	Allowance for Loan Losses The allowance for loan losses is maintained at a level that management believes is adequate to absorb probable losses inherent in the loan portfolio. Loan losses are charged against the allowance when they are known. Subsequent recoveries are credited to the allowance. Management’s determination of the adequacy of the allowance is based on an evaluation of the portfolio, current economic conditions, growth, composition of the loan portfolio, homogeneous pools of loans, risk ratings of specific loans, historical loan loss factors, identified impaired loans and other factors related to the portfolio. This evaluation is performed quarterly and is inherently subjective, as it requires various material estimates that are susceptible to significant change, including the amounts and timing of future cash flows expected to be received on any impaired loans. In addition, regulatory agencies, as an integral part of their examination process, will periodically review the Company’s allowance for loan losses, and may require the Company to record additions to the allowance based on their judgment about information available to them at the time of their examinations.
Premises and Equipment Policy	Premises and Equipment Land is carried at cost. Buildings and equipment are carried at cost, less accumulated depreciation computed on a straight-line method over the useful lives of the assets or the expected terms of the leases, if shorter. Expected terms include lease option periods to the extent that the exercise of such options is reasonably assured.
Other Real Estate Owned Policy	Other Real Estate Owned Other real estate owned (“OREO”) includes properties acquired through, or in lieu of, loan foreclosure that are held for sale and are initially recorded at the lower of the loan’s carrying amount or fair value less cost to sell at the date of foreclosure, establishing a new cost basis. Subsequent to foreclosure, valuations are periodically performed by management and the assets are carried at the lower of carrying value amount or fair value less cost to sell. Gains or losses realized upon sale of OREO and additional losses related to subsequent valuation adjustments are determined on a specific property basis and are included as a component of noninterest expense along with holding costs.
Nonmarketable Equity Investments Policy	Nonmarketable equity investments Nonmarketable equity investments include equity securities that are not publicly traded and securities acquired for various purposes. The Bank is required to maintain certain minimum levels of equity investments with certain regulatory and other entities in which the Bank has an ongoing business relationship based on the Bank’s common stock and surplus (with regard to the relationship with the Federal Reserve Bank) or outstanding borrowings (with regard to the relationship with the Federal Home Loan Bank of Atlanta). These nonmarketable equity securities are accounted for at cost which equals par or redemption value. These securities do not have a readily determinable fair value as their ownership is restricted and there is no market for these securities. These securities can only be redeemed or sold at their par value and only to the respective issuing government supported institution or to another member institution. The Company records these nonmarketable equity securities as a component of other assets, which are periodically evaluated for impairment. Management considers these nonmarketable equity securities to be long-term investments. Accordingly, when evaluating these securities for impairment, management considers the ultimate recoverability of the par value rather than by recognizing temporary declines in value.
Transfers and Servicing of Financial Assets, Policy	Transfers of Financial Assets Transfers of an entire financial asset (i.e. loan sales), a group of entire financial assets, or a participating interest in an entire financial asset (i.e. loan participations sold) are accounted for as sales when control over the assets have been surrendered. Control over transferred assets is deemed to be surrendered when (1) the assets have been isolated from the Company, (2) the transferee obtains the right (free of conditions that constrain it from taking that right) to pledge or exchange the transferred assets, and (3) the Company does not maintain effective control over the transferred assets through an agreement to repurchase them before their maturity.
Mortgage Servicing Rights Policy	Mortgage Servicing Rights The Company recognizes as assets the rights to service mortgage loans for others, known as MSRs. The Company determines the fair value of MSRs at the date the loan is transferred. An estimate of the Company’s MSRs is determined using assumptions that market participants would use in estimating future net servicing income, including estimates of prepayment speeds, discount rate, default rates, cost to service, escrow account earnings, contractual servicing fee income, ancillary income, and late fees. Subsequent to the date of transfer, the Company has elected to measure its MSRs under the amortization method. Under the amortization method, MSRs are amortized in proportion to, and over the period of, estimated net servicing income. The amortization of MSRs is analyzed monthly and is adjusted to reflect changes in prepayment speeds, as well as other factors. MSRs are evaluated for impairment based on the fair value of those assets. Impairment is determined by stratifying MSRs into groupings based on predominant risk characteristics, such as interest rate and loan type. If, by individual stratum, the carrying amount of the MSRs exceeds fair value, a valuation allowance is established through a charge to earnings. The valuation allowance is adjusted as the fair value changes. MSRs are included in the other assets category in the accompanying consolidated balance sheets.
Derivative Instruments Policy	Derivative Instruments In accordance with Accounting Standards Codification (“ASC”) Topic 815, Derivatives and Hedging, all derivative instruments are recorded on the consolidated balance sheet at their respective fair values. The accounting for changes in fair value (i.e., gains or losses) of a derivative instrument depends on whether it has been designated and qualifies as part of a hedging relationship and, if so, on the reason for holding it. If the derivative instrument is not designated as part of a hedging relationship, the gain or loss on the derivative instrument is recognized in earnings in the period of change. None of the derivatives utilized by the Company have been designated as a hedge.
Securities Sold Under Agreements to Repurchase Policy	Securities sold under agreements to repurchase Securities sold under agreements to repurchase generally mature less than one year from the transaction date. Securities sold under agreements to repurchase are reflected as a secured borrowing in the accompanying consolidated balance sheets at the amount of cash received in connection with each transaction.
Income Taxes Policy	Income Taxes Deferred tax assets and liabilities are the expected future tax amounts for the temporary differences between carrying amounts and tax bases of assets and liabilities, computed using enacted tax rates. A valuation allowance, if needed, reduces deferred tax assets to the amount expected to be realized. The net deferred tax asset is reflected as a component of other assets in the accompanying consolidated balance sheets. Income tax expense or benefit for the year is allocated among continuing operations and other comprehensive income (loss), as applicable. The amount allocated to continuing operations is the income tax effect of the pretax income or loss from continuing operations that occurred during the year, plus or minus income tax effects of (1) changes in certain circumstances that cause a change in judgment about the realization of deferred tax assets in future years, (2) changes in income tax laws or rates, and (3) changes in income tax status, subject to certain exceptions. The amount allocated to other comprehensive income (loss) is related solely to changes in the valuation allowance on items that are normally accounted for in other comprehensive income (loss) such as unrealized gains or losses on available-for-sale securities. In accordance with ASC 740, Income Taxes, a tax position is recognized as a benefit only if it is “more likely than not” that the tax position would be sustained in a tax examination, with a tax examination being presumed to occur. The amount recognized is the largest amount of tax benefit that is greater than 50% likely of being realized on examination. For tax positions not meeting the “more likely than not” test, no tax benefit is recorded. It is the Company’s policy to recognize interest and penalties related to income tax matters in income tax expense. The Company and its wholly-owned subsidiaries file a consolidated income tax return.
Income Taxes, Uncertainties Policy	In accordance with ASC 740, Income Taxes, a tax position is recognized as a benefit only if it is “more likely than not” that the tax position would be sustained in a tax examination, with a tax examination being presumed to occur. The amount recognized is the largest amount of tax benefit that is greater than 50% likely of being realized on examination. For tax positions not meeting the “more likely than not” test, no tax benefit is recorded. It is the Company’s policy to recognize interest and penalties related to income tax matters in income tax expense. The Company and its wholly-owned subsidiaries file a consolidated income tax return.
Fair Value Measurements Policy	Fair Value Measurements ASC 820, Fair Value Measurements, which defines fair value, establishes a framework for measuring fair value in U.S. generally accepted accounting principles and expands disclosures about fair value measurements. ASC 820 applies only to fair-value measurements that are already required or permitted by other accounting standards. The definition of fair value focuses on the exit price, i.e., the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date, not the entry price, i.e., the price that would be paid to acquire the asset or received to assume the liability at the measurement date. The statement emphasizes that fair value is a market-based measurement; not an entity-specific measurement. Therefore, the fair value measurement should be determined based on the assumptions that market participants would use in pricing the asset or liability. For more information related to fair value measurements, please refer to Note 16, Fair Value.
Subsequent Events Policy	Subsequent Events The Company has evaluated the effects of events or transactions through the date of this filing that have occurred subsequent to December 31, 2018. The Company does not believe there are any material subsequent events that would require further recognition or disclosure.