Basis of Presentation (Policies)	3 Months Ended
Basis of Presentation (Policies)	Mar. 31, 2025
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 subsidiaries (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 March 31, 2025 and December 31, 2024, and the results of its operations for the three months ended March 31, 2025 and 2024. Interim results do not necessarily represent annual results. Certain information and disclosures normally included in notes to consolidated annual financial statements prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) have been condensed or omitted in this Quarterly Report on Form 10-Q pursuant to SEC rules and regulations. These financial statements should be read in conjunction with Old National’s Annual Report on Form 10-K for the year ended December 31, 2024. All intercompany transactions and balances have been eliminated.
Recent Accounting Pronouncements	RECENT ACCOUNTING PRONOUNCEMENTS Accounting Guidance Pending Adoption Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 740 – In December 2023, the FASB issued Accounting Standards Update (“ASU”) 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. Among other things, these amendments require that public business entities on an annual basis disclose additional information in specified categories with respect to the reconciliation of the effective tax rate to the statutory rate for federal, state, and foreign income taxes. It also requires greater detail about individual reconciling items in the rate reconciliation to the extent the impact of those items exceeds a quantitative threshold (if the effect of those reconciling items is equal to or greater than 5 percent of the amount computed by multiplying pretax income (loss) by the applicable statutory income tax rate). In addition, the ASU requires information pertaining to taxes paid (net of refunds received) to be disaggregated for federal, state, and foreign taxes and further disaggregated for specific jurisdictions to the extent the related amounts are equal to or greater than 5 percent of total income taxes paid (net of refunds received). The amendments in this ASU are effective for annual periods beginning after December 15, 2024. Old National does not expect the adoption of this guidance will have a material impact on the consolidated financial statements. FASB ASC 220 – In November 2024, the FASB issued ASU 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses. This ASU requires public business entities to disclose specified information about certain costs and expenses in the notes to financial statements at each interim and annual reporting period. Specifically, public business entities will be required to disclose the amounts of (a) purchases of inventory; (b) employee compensation; (c) depreciation; (d) intangible asset amortization; and (e) depreciation, depletion, and amortization recognized as part of oil- and gas-producing activities (or other amounts of depletion expense) included in each relevant expense caption. Within the same tabular disclosure, an entity must disclose certain expense, gain, or loss amounts that are already required under current GAAP. Further, an entity must disclose a qualitative description of the amounts remaining in relevant expense captions that are not separately disaggregated quantitatively. In addition, an entity must disclose the total amount of selling expenses and, in annual reporting periods, an entity’s definition of selling expenses. The amendments in this ASU are effective for annual periods beginning after December 15, 2026, and interim periods within fiscal years beginning after December 15, 2027. Early adoption is permitted. Old National is currently evaluating the impact of adopting this guidance on the consolidated financial statements. FASB ASC 470 – In November 2024, the FASB issued ASU 2024-04, Debt—Debt with Conversion and Other Options (Subtopic 470-20): Induced Conversions of Convertible Debt Instruments. This ASU clarifies requirements for determining whether certain settlements of convertible debt instruments, including convertible debt instruments with cash conversion features or convertible debt instruments that are not currently convertible, should be accounted for as an induced conversion. The amendments in this ASU are effective for annual periods beginning after December 15, 2025, and interim periods within those annual reporting periods. Old National is currently evaluating the impact of adopting this guidance on the consolidated financial statements.