Commercial real estate loans as a percentage of risk-based capital.

No definition available.

Name:	onb_CommercialRealEstateLoansAsPercentageOfRiskBasedCapital
Namespace Prefix:	onb_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The regulatory guideline limit for commercial real estate loans as a percentage of risk-based capital.

+ References

No definition available.

+ Details

Name:	onb_CommercialRealEstateLoansAsPercentageOfRiskBasedCapitalRegulatoryGuideLineLimit
Namespace Prefix:	onb_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Maximum number of days past due before loan is placed on nonaccrual status.

+ References

No definition available.

+ Details

Name:	onb_FinanceReceivablePastDuePeriodForNonaccrualStatus
Namespace Prefix:	onb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing Receivable, Number Of Loan Portfolios

+ References

No definition available.

+ Details

Name:	onb_FinancingReceivableNumberOfLoanPortfolios
Namespace Prefix:	onb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Financing Receivable, Number Of Loan Segments

+ References

No definition available.

+ Details

Name:	onb_FinancingReceivableNumberOfLoanSegments
Namespace Prefix:	onb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of loan participations with other financial institutions.

+ References

No definition available.

+ Details

Name:	onb_LoanParticipations
Namespace Prefix:	onb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of loan participations retained.

+ References

No definition available.

+ Details

Name:	onb_LoanParticipationsRetained
Namespace Prefix:	onb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of loan participations sold to other financial institutions.

+ References

No definition available.

+ Details

Name:	onb_LoanParticipationsSold
Namespace Prefix:	onb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, before allowance for credit loss, of accrued interest on financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 3B
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447

+ Details

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

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

+ Details

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

No definition available.

+ Details

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

- Definition

Amount of unfunded portion of contractual agreement to lend funds to borrower for financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=121585226&loc=d3e18794-111554

+ Details

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

- Definition

Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(2)
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI https://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585

+ Details

Name:	us-gaap_ProvisionForLoanLeaseAndOtherLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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

Loans and Allowance for Credit Losses - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($) portfolio segment	Mar. 31, 2022 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of loan portfolios \| portfolio	4
Number of loan segments \| segment	7
Accrued interest receivable on loans	$ 144,100		$ 137,700
Provision for loan losses	0	$ 78,531
Allowance for credit losses	$ 298,711	280,507	303,671	$ 107,341
Loan placed on nonaccrual when past due, number of days	90 days
Loan participations	$ 2,600,000
Loan participations sold	1,200,000
Loan participations retained	1,400,000
Unfunded commitments on TDRs	$ 0
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Percentage of risk-based capital	234.00%
Regulatory guideline limit	300.00%
Provision for loan losses	$ 0	42,601
Allowance for credit losses	$ 135,348	$ 140,490	$ 138,244	$ 64,004