Name:	onb_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetAccretionAmortizationOfDiscountOrPremium
Namespace Prefix:	onb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Credit Loss Write Downs

No definition available.

Name:	onb_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetCreditLossWriteDowns
Namespace Prefix:	onb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Fair value measurement with unobservable inputs reconciliation recurring basis asset matured securities.

No definition available.

Name:	onb_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetMaturedSecurities
Namespace Prefix:	onb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Payments Received

No definition available.

Name:	onb_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPaymentsReceived
Namespace Prefix:	onb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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

Amount of increase (decrease) of assets measured at fair value on a recurring basis using unobservable inputs (level 3). Such increase (decrease) may be comprised of changes in fair value (gains or losses) whether realized or unrealized that have been included in earnings, changed net asset value, or other comprehensive income (a separate component of shareholders' equity); purchases, sales, issues, or settlements of assets; and net transfers in to or out of this category within the fair value hierarchy.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c(1), c(2), c(3)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.