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/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph c
-Publisher SEC

Reference 2: 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

+ 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

- Definition

The aggregate interest and fee income generated by: (1) loans the Entity has positive intent and ability to hold for the foreseeable future, or until maturity or payoff, including commercial and consumer loans, whether domestic or foreign, which may consist of: (a) industrial and agricultural; (b) real estate; and (c) real estate construction loans; (d) trade financing; (e) lease financing; (f) home equity lines-of-credit; (g) automobile and other vehicle loans; and (h) credit card and other revolving-type loans and (2) loans and leases held-for-sale which may include mortgage loans, direct financing, and sales-type leases.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478524/942-220-S99-1

+ Details

Name:	us-gaap_InterestAndFeeIncomeLoansAndLeases
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2022
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	$ 36,400,643		$ 36,400,643		$ 32,991,927
Allowance for credit losses on loans	(380,840)	$ (303,982)	(380,840)	$ (303,982)	(307,610)	$ (366,335)	$ (300,555)	$ (303,671)
Net loans	36,019,803		36,019,803		32,684,317
Taxable	561,428	474,387	1,594,411	1,334,658
Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	0		0		0
Net loans	0		0		0
Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	36,400,643		36,400,643		32,991,927
Allowance for credit losses on loans	(380,840)		(380,840)		(307,610)
Net loans	36,019,803		36,019,803		32,684,317
Taxable			183,400		93,700
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	10,408,095		10,408,095		9,512,230
Allowance for credit losses on loans	(136,842)	(124,755)	(136,842)	(124,755)	(118,333)	(138,460)	(127,403)	(120,612)
Commercial \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	(224,732)		(224,732)		(232,764)
Commercial \| Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	10,183,363		10,183,363		9,279,466
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	16,356,216		16,356,216		14,140,629
Allowance for credit losses on loans	(204,899)	(144,975)	(204,899)	(144,975)	(155,099)	(189,911)	(136,897)	(138,244)
Commercial real estate \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	(175,628)		(175,628)		(169,058)
Commercial real estate \| Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	16,180,588		16,180,588		13,971,571
BBCC
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses on loans	(2,692)	(2,709)	(2,692)	(2,709)	(2,887)	(2,897)	(2,776)	(2,431)
BBCC \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	400,360		400,360		401,822
BBCC \| Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	400,360		400,360		401,822
Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	6,757,896		6,757,896		6,699,443
Allowance for credit losses on loans	(21,488)	(20,780)	(21,488)	(20,780)	(20,837)	(23,135)	(20,421)	(21,916)
Residential real estate \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	0		0		0
Residential real estate \| Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	6,757,896		6,757,896		6,699,443
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	2,878,436		2,878,436		2,639,625
Consumer \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	(2,878,436)		(2,878,436)		(2,639,625)
Indirect
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	1,096,234		1,096,234		1,050,982
Allowance for credit losses on loans	(5,661)	(1,321)	(5,661)	(1,321)	(1,236)	(1,233)	(1,407)	(1,532)
Indirect \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	1,096,234		1,096,234		1,050,982
Indirect \| Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	1,096,234		1,096,234		1,050,982
Direct
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	419,201		419,201		523,172
Allowance for credit losses on loans	(2,427)	(3,571)	(2,427)	(3,571)	(3,169)	(3,131)	(4,755)	(12,116)
Direct \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	419,201		419,201		523,172
Direct \| Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	419,201		419,201		523,172
Home equity
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	1,363,001		1,363,001		1,065,471
Allowance for credit losses on loans	(6,831)	$ (5,871)	(6,831)	$ (5,871)	(6,049)	$ (7,568)	$ (6,896)	$ (6,820)
Home equity \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	1,363,001		1,363,001		1,065,471
Home equity \| Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	1,363,001		1,363,001		1,065,471
Direct Finance Leases
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans, net of unearned income	$ 133,600		$ 133,600		$ 169,700