Other Borrowings - Summary of Other Borrowings (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Finance lease liabilities	$ 25,410	$ 24,822
Other borrowings	825,425	689,618
Old National Bank
Debt Instrument [Line Items]
Other basis adjustments	23,126	112,853
Finance lease liabilities	25,410	24,822
Derivative collateralize position amount	$ 23,100	112,800
Old National Bank \| Subordinated Debt
Debt Instrument [Line Items]
Variable rates	8.93%
Variable rate	4.618%
Subordinated debentures	$ 12,000	12,000
Old National Bank \| Leveraged Loans for NMTC
Debt Instrument [Line Items]
Leveraged loans for NMTC (fixed rates of 1.00% to 7.25%) maturing December 2027 to June 2060	$ 407,209	210,251
Old National Bank \| Leveraged Loans for NMTC \| Minimum
Debt Instrument [Line Items]
Fixed rates	1.00%
Old National Bank \| Leveraged Loans for NMTC \| Maximum
Debt Instrument [Line Items]
Fixed rates	7.25%
Old National Bancorp
Debt Instrument [Line Items]
Other basis adjustments	$ 9,181	13,049
Old National Bancorp \| Subordinated Debt \| Subordinated Debentures, Due September 2026
Debt Instrument [Line Items]
Fixed rates	5.88%
Subordinated debentures	$ 150,000	150,000
Old National Bancorp \| Subordinated Debt \| Subordinated debentures redeemed in September 2025
Debt Instrument [Line Items]
Subordinated debentures	0	30,000
Old National Bancorp \| Junior Subordinated Debentures
Debt Instrument [Line Items]
Junior subordinated debentures (rates of 5.70% to 8.15%) maturing July 2031 to September 2037	$ 198,499	$ 136,643
Old National Bancorp \| Junior Subordinated Debentures \| Minimum
Debt Instrument [Line Items]
Variable rates	5.70%
Old National Bancorp \| Junior Subordinated Debentures \| Maximum
Debt Instrument [Line Items]
Variable rates	8.15%

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