Basis of Presentation (Policies)	9 Months Ended
Basis of Presentation (Policies)	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	BASIS OF PRESENTATION The accompanying unaudited consolidated financial statements include the accounts of Old National Bancorp and its wholly-owned affiliates (hereinafter collectively referred to as “Old National”) and have been prepared in conformity with accounting principles generally accepted in the United States of America and prevailing practices within the banking industry. Such principles require management to make estimates and assumptions that affect the reported amounts of assets, liabilities, and the disclosures of contingent assets and liabilities at the date of the financial statements and amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. In the opinion of management, the consolidated financial statements contain all the normal and recurring adjustments necessary for a fair statement of the financial position of Old National as of September 30, 2021 and December 31, 2020, and the results of its operations for the three and nine months ended September 30, 2021 and 2020. Interim results do not necessarily represent annual results. These financial statements should be read in conjunction with Old National’s Annual Report on Form 10-K for the year ended December 31, 2020. All significant intercompany transactions and balances have been eliminated. Certain prior year amounts have been reclassified to conform to the current presentation. Such reclassifications had no effect on prior period net income or shareholders’ equity and were insignificant amounts.
Recent Accounting Pronouncements	RECENT ACCOUNTING PRONOUNCEMENTS Accounting Guidance Adopted in 2021 FASB ASC 715 – In August 2018, the FASB issued ASU No. 2018-14, Compensation – Retirement Benefits – Defined Benefit Plans – General (Subtopic 715-20): Disclosure Framework – Changes to the Disclosure Requirements for Defined Benefit Plans. The amendments in this update modify the disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans. The amendments in this update became effective for fiscal years ending after December 15, 2020 and did not have a material impact on the financial statements. FASB ASC 740 – In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. This ASU removes specific exceptions to the general principles in Topic 740 in GAAP. It eliminates the need for an organization to analyze whether the following apply in a given period: (1) exception to the incremental approach for intraperiod tax allocation; (2) exceptions to accounting for basis differences when there are ownership changes in foreign investments; and (3) exception in interim period income tax accounting for year-to-date losses that exceed anticipated losses. The ASU also improves financial statement preparers’ application of income tax-related guidance and simplifies GAAP for: (1) franchise taxes that are partially based on income; (2) transactions with a government that result in a step up in the tax basis of goodwill; (3) separate financial statements of legal entities that are not subject to tax; and (4) enacted changes in tax laws in interim periods. The amendments in this update became effective for fiscal years beginning after December 15, 2020, and interim periods within those fiscal years and did not have a material impact on the financial statements. FASB ASC 321, 323, and 815 – In January 2020, the FASB issued ASU No. 2020-01, Investments – Equity Securities (Topic 321), Investments – Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815) – Clarifying the Interactions Between Topic 321, Topic 323, and Topic 815 (a Consensus of the Emerging Issues Task Force). The ASU clarifies the interaction between ASU 2016-01, Financial Instruments – Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities and the ASU on equity method investments. ASU 2016-01 provides companies with an alternative to measure certain equity securities without a readily determinable fair value at cost, minus impairment, if any, unless an observable transaction for an identical or similar security occurs. ASU 2020-01 clarifies that for purposes of applying the Topic 321 measurement alternative, an entity should consider observable transactions that require it to either apply or discontinue the equity method of accounting under Topic 323, immediately before applying or upon discontinuing the equity method. In addition, the new ASU provides direction that a company should not consider whether the underlying securities would be accounted for under the equity method or the fair value option when it is determining the accounting for certain forward contracts and purchased options, upon either settlement or exercise. The amendments in this update became effective for fiscal years beginning after December 15, 2020, and interim periods within those fiscal years. The amendments are to be applied prospectively and did not have a material impact on the consolidated financial statements. Acquisitions and Dispositions of Businesses and Related Pro Forma Information – In May 2020, the SEC issued a final rule that revises the circumstances that require financial statements and related pro forma information for acquisitions and dispositions of businesses. The intent of the rule is to allow for more meaningful conclusions on when an acquired or disposed business is significant as well as to improve the related disclosure requirements. The changes are intended to improve the financial information about acquired or disposed businesses, facilitate more timely access to capital, and reduce the complexity and costs to prepare the disclosure. The final rule was effective January 1, 2021. FASB ASC 310 – In October 2020, the FASB issued ASU No. 2020-08, Codification Improvements to Subtopic 310-20, Receivables—Nonrefundable Fees and Other Costs, to clarify that an entity should reevaluate whether a callable debt security is within the scope of ASC paragraph 310-20-35-33 for each reporting period. The ASU was effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. The new guidance did not have a material impact on the consolidated financial statements. FASB ASC 470 – In October 2020, the FASB issued ASU No. 2020-09, Debt (Topic 470) Amendments to SEC Paragraphs Pursuant to SEC Release No. 33-10762, which amends and supersedes various SEC paragraphs to reflect SEC Release No. 33-10762. That release amends the financial disclosure requirements applicable to registered debt offerings that include credit enhancements, such as subsidiary guarantees. These changes are intended to both improve the quality of disclosure and increase the likelihood that issuers will conduct debt offerings on a registered basis. The final rules were effective on January 4, 2021. The amendments did not have a material impact on the consolidated financial statements. Codification Improvements – In October 2020, the FASB issued ASU No. 2020-10, Codification Improvements. The amendments improve codification by having all disclosure-related guidance available in the disclosure sections of the codification. Prior to this ASU, various disclosure requirements or options to present information on the face of the financial statements or as a note to the financial statements were not included in the appropriate disclosure sections of the codification. The codification improvements also contain various other minor amendments to codification that are not expected to have a significant effect on current accounting practice. The amendments became effective for annual periods beginning after December 15, 2020. FASB ASC 848 – In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides temporary, optional guidance to ease the potential burden in accounting for, or recognizing the effects of, the transition away from the LIBOR or other interbank offered rate on financial reporting. To help with the transition to new reference rates, the ASU provides optional expedients and exceptions for applying GAAP to affected contract modifications and hedge accounting relationships. The main provisions include: •A change in a contract’s reference interest rate would be accounted for as a continuation of that contract rather than as the creation of a new one for contracts, including loans, debt, leases, and other arrangements, that meet specific criteria. •When updating its hedging strategies in response to reference rate reform, an entity would be allowed to preserve its hedge accounting. The guidance is applicable only to contracts or hedge accounting relationships that reference LIBOR or another reference rate expected to be discontinued. Because the guidance is meant to help entities through the transition period, it will be in effect for a limited time and will not apply to contract modifications made and hedging relationships entered into or evaluated after December 31, 2022, except for hedging relationships existing as of December 31, 2022, for which an entity has elected certain optional expedients that are retained through the end of the hedging relationship. The amendments in this ASU are effective March 12, 2020 through December 31, 2022. ASU 2020-04 permits relief solely for reference rate reform actions and permits different elections over the effective date for legacy and new activity. Accordingly, Old National is evaluating and reassessing the elections on a quarterly basis. For current elections in effect regarding the assertion of the probability of forecasted transactions, Old National elects the expedient to assert the probability of the hedged interest payments and receipts regardless of any expected modification in terms related to reference rate reform. In January 2021, the FASB issued ASU 2021-01, Reference Rate Reform (Topic 848): Scope, which addresses questions about whether Topic 848 can be applied to derivative instruments that do not reference a rate that is expected to be discontinued but that use an interest rate for margining, discounting, or contract price alignment that is expected to be modified as a result of reference rate reform, commonly referred to as the “discounting transition.” The amendments clarify that certain optional expedients and exceptions in Topic 848 do apply to derivatives that are affected by the discounting transition. The amendments in ASU 2021-01 are effective immediately. Old National believes the adoption of this guidance on activities subsequent to September 30, 2021 through December 31, 2022 will not have a material impact on the consolidated financial statements. Guidance on Non-TDR Loan Modifications due to COVID-19 – The CAA, which was signed into law on December 27, 2020, extends certain provisions of the CARES Act. Section 4013 of the CARES Act provided temporary relief from TDR accounting and is amended by Division N, Section 540 of the CAA, by extending the end date from December 31, 2020, to the earlier of January 1, 2022, or 60 days after the date on which the COVID-19 national emergency terminates. In response, the OCC updated its two-page reference guide, “TDR Designation and COVID-19 Loan Modifications,” to conform to the extended TDR provisions. In accordance with such guidance, we are offering short-term modifications made in response to COVID-19 to borrowers who are current and otherwise not past due. These include short-term (180 days or less) modifications in the form of payment deferrals, fee waivers, extensions of repayment terms, or other delays in payment that are insignificant. See Note 6 for further information on non-TDR loan modifications. Accounting Guidance Pending Adoption FASB ASC 470 and 815 – In August 2020, the FASB issued ASU 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging— Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity, to clarify the accounting for certain financial instruments with characteristics of liabilities and equity. The amendments in this update reduce the number of accounting models for convertible debt instruments and convertible preferred stock by removing the cash conversion model and the beneficial conversion feature model. Limiting the accounting models will result in fewer embedded conversion features being separately recognized from the host contract. Convertible instruments that continue to be subject to separation models are (1) those with embedded conversion features that are not clearly and closely related to the host contract, that meet the definition of a derivative, and that do not qualify for a scope exception from derivative accounting and (2) convertible debt instruments issued with substantial premiums for which the premiums are recorded as paid-in-capital. In addition, this ASU improves disclosure requirements for convertible instruments and earnings-per-share guidance. The ASU also revises the derivative scope exception guidance to reduce form-over-substance-based accounting conclusions driven by remote contingent events. The amendments in this update are effective for fiscal years beginning after December 15, 2021, and interim periods within those fiscal years. Early adoption will be permitted, but no earlier than for fiscal years beginning after December 15, 2020. Old National is currently evaluating the impact of adopting the new guidance on the consolidated financial statements. FASB ASC 842 – In July 2021, the FASB issued ASU 2021-05, Leases (Topic 842): Lessors—Certain Leases with Variable Lease Payments, to amend the lease classification requirements for lessors to align them with practice under ASC Topic 840. Lessors should classify and account for a lease with variable lease payments that do not depend on a reference index or a rate as an operating lease if both of the following criteria are met: (1) The lease would have been classified as a sales-type lease or a direct financing lease in accordance with the classification criteria in ASC paragraphs 842-10-25-2 through 25-3; and (2) The lessor would have otherwise recognized a day-one loss. When a lease is classified as operating, the lessor does not recognize a net investment in the lease, does not derecognize the underlying asset, and, therefore, does not recognize a selling profit or loss. The amendments in this update are effective for fiscal years beginning after December 15, 2021, and interim periods within those fiscal years. Early adoption is permitted. Old National is currently evaluating the impact of adopting the new guidance on the consolidated financial statements. FASB ASC 205, 942, and 946 – In August 2021, the FASB issued ASU 2021-06, Presentation of Financial Statements (Topic 205), Financial Services—Depository and Lending (Topic 942), and Financial Services—Investment Companies (Topic 946): Amendments to SEC Paragraphs Pursuant to SEC Final Rule Releases No. 33-10786, Amendments to Financial Disclosures about Acquired and Disposed Businesses, and No. 33-10835, Update of Statistical Disclosures for Bank and Savings and Loan Registrants. This ASU incorporates recent SEC rule changes into the FASB Codification, including SEC Final Rule Releases No. 33-10786, Amendments to Financial Disclosures about Acquired and Disposed Businesses, and No. 33-10835, Update of Statistical Disclosures for Bank and Savings and Loan Registrants. The amendments in this update are effective upon addition to the FASB Codification and will not have a material impact on the consolidated financial statements.