Other Borrowings - Summary of Other Borrowings (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Finance lease liabilities	$ 21,207	$ 24,822
Other borrowings	872,297	689,618
Old National Bank
Debt Instrument [Line Items]
Other basis adjustments	51,628	112,853
Finance lease liabilities	21,207	24,822
Derivative collateralize position amount	$ 51,600	112,800
Old National Bank | Subordinated Debt
Debt Instrument [Line Items]
Variable rates	8.90%
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	$ 398,493	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	$ 10,470	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 Debt Due on June 2030
Debt Instrument [Line Items]
Fixed rates	9.69%
Subordinated debentures	$ 30,000	30,000
Old National Bancorp | Junior Subordinated Debentures
Debt Instrument [Line Items]
Junior subordinated debentures (rates of 5.98% to 8.12%) maturing July 2031 to September 2037	$ 198,499	$ 136,643
Old National Bancorp | Junior Subordinated Debentures | Minimum
Debt Instrument [Line Items]
Variable rates	5.98%
Old National Bancorp | Junior Subordinated Debentures | Maximum
Debt Instrument [Line Items]
Variable rates	8.12%