Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph c
-Publisher SEC

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amortized cost excluding accrued interest, after allowance for credit loss, of financing receivable. Excludes net investment in lease.

+ References

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479344/326-20-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-3B

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-5

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_ReclassificationTypeAxis=onb_SegmentPortfolioReclassificationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ReclassificationTypeAxis=onb_SegmentPortfolioReclassificationAdjustedBalanceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=onb_BusinessBankingCreditCenterPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=onb_IndirectPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=onb_DirectPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=onb_HomeEquityPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_FinanceLeasesPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans and Allowance for Credit Losses - Schedule of Composition of Loans and Impact of Adoption (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 32,432,473		$ 31,123,641
Allowance for credit losses on loans	(300,555)	$ (298,711)	(303,671)	$ (288,003)	$ (280,507)	$ (107,341)
Net loans	32,131,918		30,819,970
Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	0		0
After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	32,432,473		31,123,641
Allowance for credit losses on loans	(300,555)		(303,671)
Net loans	32,131,918		30,819,970
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	9,698,241		9,508,904
Allowance for credit losses on loans	(127,403)	(125,768)	(120,612)	(102,819)	(99,471)	(27,232)
Commercial \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	(227,414)		(210,280)
Commercial \| After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	9,470,827		9,298,624
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	13,450,209		12,457,070
Allowance for credit losses on loans	(136,897)	(135,348)	(138,244)	(141,802)	(140,490)	(64,004)
Commercial real estate \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	(162,841)		(158,322)
Commercial real estate \| After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	13,287,368		12,298,748
BBCC
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses on loans	(2,776)	(2,316)	(2,431)	(2,064)	(2,069)	(2,458)
BBCC \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	390,255		368,602
BBCC \| After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	390,255		368,602
Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	6,684,480		6,460,441
Allowance for credit losses on loans	(20,421)	(20,207)	(21,916)	(19,729)	(17,252)	(9,347)
Residential real estate \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	0		0
Residential real estate \| After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	6,684,480		6,460,441
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	2,599,543		2,697,226
Consumer \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	(2,599,543)		(2,697,226)
Indirect
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,003,287		1,034,257
Allowance for credit losses on loans	(1,407)	(1,434)	(1,532)	(1,641)	(1,648)	(1,743)
Indirect \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,003,287		1,034,257
Indirect \| After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,003,287		1,034,257
Direct
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	565,950		629,186
Allowance for credit losses on loans	(4,755)	(6,766)	(12,116)	(14,412)	(14,450)	(528)
Direct \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	565,950		629,186
Direct \| After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	565,950		629,186
Home equity
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,030,306		1,033,783
Allowance for credit losses on loans	(6,896)	$ (6,872)	(6,820)	$ (5,536)	$ (5,127)	$ (2,029)
Home equity \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,030,306		1,033,783
Home equity \| After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,030,306		1,033,783
Direct Finance Leases
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 176,700		$ 188,100