Name:	onb_DebtSecuritiesLowestCreditRating
Namespace Prefix:	onb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The actual deferrals and defaults on pooled trust preferred securities as a percentage of original collateral.

No definition available.

Name:	onb_PooledTrustPreferredSecuritiesActualDeferralsAndDefaultsAsPercentageOfOriginalCollateral
Namespace Prefix:	onb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The class categorization on the pooled trust preferred securities.

No definition available.

Name:	onb_PooledTrustPreferredSecuritiesClass
Namespace Prefix:	onb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The excess subordination on pooled trust preferred securities as a percentage of current performing collateral.

No definition available.

Name:	onb_PooledTrustPreferredSecuritiesExcessSubordinationAsPercentageOfCurrentPerformingCollateral
Namespace Prefix:	onb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The expected defaults on pooled trust preferred securities as a percentage of remaining performing collateral.

No definition available.

Name:	onb_PooledTrustPreferredSecuritiesExpectedDefaultsAsPercentageOfRemainingPerformingCollateral
Namespace Prefix:	onb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The number of issuers of the pooled trust preferred securities that are currently performing.

No definition available.

Name:	onb_PooledTrustPreferredSecuritiesNumberOfIssuersCurrentlyPerforming
Namespace Prefix:	onb_
Data Type:	xbrli:integerItemType
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Period Type:	instant

The number of issuers of the pooled trust preferred securities that are currently remaining.

No definition available.

Name:	onb_PooledTrustPreferredSecuritiesNumberOfIssuersCurrentlyRemaining
Namespace Prefix:	onb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Schedule of available for sale and held to maturity securities.

No definition available.

Name:	onb_ScheduleOfAvailableForSaleAndHeldToMaturitySecuritiesLineItems
Namespace Prefix:	onb_
Data Type:	xbrli:stringItemType
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Period Type:	duration

Amount before tax of unrealized gain (loss) in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

No definition available.

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

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

No definition available.

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

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

No definition available.

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

Name:	us-gaap_FinancialInstrumentAxis=onb_PooledTrustPreferredSecuritiesOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	us-gaap_DebtInstrumentAxis=onb_PretslTwelveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_DebtInstrumentAxis=onb_TrapezaSerThirteenaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancialInstrumentAxis=onb_SingleIssuerTrustPreferredSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_DebtInstrumentAxis=onb_JpMorganChaseCapThirteenMember
Namespace Prefix:
Data Type:	na
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