Regulatory Restrictions - Schedule of Capital Ratios (Details) $ in Thousands	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Old National Bancorp
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total capital to risk-weighted assets actual, amount	$ 4,727,216	$ 4,321,716
Common equity Tier 1 capital to risk-weighted assets actual, amount	4,003,694	3,605,393
Tier 1 capital to risk-weighted assets actual, amount	4,247,413	3,849,112
Tier 1 capital to average assets actual, amount	$ 4,247,413	$ 3,849,112
Total capital to risk-weighted assets actual, ratio	0.1264	0.1202
Common equity Tier 1 capital to risk-weighted assets actual, ratio	10.70%	10.03%
Tier 1 capital to risk-weighted assets actual, ratio	0.1135	0.1071
Tier 1 capital to average assets actual, ratio	0.0883	0.0852
Total capital to risk-weighted assets fully phased-in regulatory guidelines minimum, amount	$ 3,927,771	$ 3,774,845
Common equity Tier 1 capital to risk-weighted assets fully phased-in regulatory guidelines minimum, amount	2,618,514	2,516,563
Tier 1 capital to risk-weighted assets fully phased-in regulatory guidelines minimum, amount	3,179,625	3,055,827
Tier 1 capital to average assets fully phased-in regulatory guidelines minimum, amount	$ 1,923,360	$ 1,808,108
Total capital to risk-weighted assets fully phased-in regulatory guidelines minimum, ratio	0.1050	0.1050
Common equity Tier 1 capital to risk-weighted assets fully phased-in regulatory guidelines minimum, ratio	7.00%	7.00%
Tier 1 capital to risk-weighted assets fully phased-in regulatory guidelines minimum, ratio	0.0850	0.0850
Tier 1 capital to average assets fully phased-in regulatory guidelines minimum, ratio	0.0400	0.0400
Total capital to risk-weighted assets well capitalized guidelines, amount	$ 3,740,735	$ 3,595,090
Tier 1 capital to risk-weighted assets well capitalized guidelines, amount	$ 2,244,441	$ 2,157,054
Total capital to risk-weighted assets well capitalized guidelines, ratio	0.1000	0.1000
Tier 1 capital to risk-weighted assets well capitalized guidelines, ratio	0.0600	0.0600
Old National Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total capital to risk-weighted assets actual, amount	$ 4,591,734	$ 4,063,363
Common equity Tier 1 capital to risk-weighted assets actual, amount	4,308,574	3,817,402
Tier 1 capital to risk-weighted assets actual, amount	4,308,574	3,817,402
Tier 1 capital to average assets actual, amount	$ 4,308,574	$ 3,817,402
Total capital to risk-weighted assets actual, ratio	0.1233	0.1135
Common equity Tier 1 capital to risk-weighted assets actual, ratio	11.57%	10.66%
Tier 1 capital to risk-weighted assets actual, ratio	0.1157	0.1066
Tier 1 capital to average assets actual, ratio	0.0899	0.0847
Total capital to risk-weighted assets fully phased-in regulatory guidelines minimum, amount	$ 3,911,089	$ 3,759,671
Common equity Tier 1 capital to risk-weighted assets fully phased-in regulatory guidelines minimum, amount	2,607,393	2,506,448
Tier 1 capital to risk-weighted assets fully phased-in regulatory guidelines minimum, amount	3,166,120	3,043,544
Tier 1 capital to average assets fully phased-in regulatory guidelines minimum, amount	$ 1,916,002	$ 1,803,426
Total capital to risk-weighted assets fully phased-in regulatory guidelines minimum, ratio	0.1050	0.1050
Common equity Tier 1 capital to risk-weighted assets fully phased-in regulatory guidelines minimum, ratio	7.00%	7.00%
Tier 1 capital to risk-weighted assets fully phased-in regulatory guidelines minimum, ratio	0.0850	0.0850
Tier 1 capital to average assets fully phased-in regulatory guidelines minimum, ratio	0.0400	0.0400
Total capital to risk-weighted assets well capitalized guidelines, amount	$ 3,724,847	$ 3,580,639
Common equity Tier 1 capital to risk-weighted assets well capitalized guidelines, amount	2,421,150	2,327,416
Tier 1 capital to risk-weighted assets well capitalized guidelines, amount	2,979,878	2,864,512
Tier 1 capital to average assets well capitalized guidelines, amount	$ 2,395,003	$ 2,254,282
Total capital to risk-weighted assets well capitalized guidelines, ratio	0.1000	0.1000
Common equity Tier 1 capital to risk-weighted assets well capitalized guidelines, ratio	6.50%	6.50%
Tier 1 capital to risk-weighted assets well capitalized guidelines, ratio	0.0800	0.0800
Tier 1 capital to average assets well capitalized guidelines, ratio	0.0500	0.0500