Finance Receivables And Allowance For Credit Losses (Schedule Of Activity In The Allowance For Loan Losses) (Details) (USD $) In Thousands				3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended
Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010	Jun. 30, 2011 Commercial [Member]	Jun. 30, 2010 Commercial [Member]	Jun. 30, 2011 Commercial [Member]	Jun. 30, 2010 Commercial [Member]	Jun. 30, 2011 Commercial Real Estate [Member]	Jun. 30, 2010 Commercial Real Estate [Member]	Jun. 30, 2011 Commercial Real Estate [Member]	Jun. 30, 2010 Commercial Real Estate [Member]	Jun. 30, 2011 Consumer [Member]	Jun. 30, 2010 Consumer [Member]	Jun. 30, 2011 Consumer [Member]	Jun. 30, 2010 Consumer [Member]	Jun. 30, 2011 Residential [Member]	Jun. 30, 2010 Residential [Member]	Jun. 30, 2011 Residential [Member]	Jun. 30, 2010 Residential [Member]	Jun. 30, 2011 Unallocated [Member]	Jun. 30, 2010 Unallocated [Member]	Jun. 30, 2011 Unallocated [Member]	Jun. 30, 2010 Unallocated [Member]	Jun. 30, 2011 Total Loans And Leases Receivable Allowance [Member]	Jun. 30, 2010 Total Loans And Leases Receivable Allowance [Member]	Jun. 30, 2011 Total Loans And Leases Receivable Allowance [Member]	Jun. 30, 2010 Total Loans And Leases Receivable Allowance [Member]
Beginning balance	$ 70,189	$ 72,309	$ 71,863	$ 27,190	$ 27,764	$ 26,204	$ 26,869	$ 32,550	$ 28,716	$ 32,654	$ 27,138	$ 10,280	$ 13,967	$ 11,142	$ 13,853	$ 2,729	$ 1,651	$ 2,309	$ 1,688	$ 0	$ 0	$ 0	$ 0	$ 72,749	$ 72,098	$ 72,309	$ 69,548
Charge-offs				(3,838)	(4,498)	(5,169)	(7,991)	(2,274)	(3,105)	(2,981)	(4,841)	(2,465)	(3,456)	(5,853)	(8,211)	(325)	(748)	(1,173)	(1,676)	0	0	0	0	(8,902)	(11,807)	(15,176)	(22,719)
Recoveries				1,302	1,208	2,135	3,458	316	853	984	1,145	1,468	1,473	3,326	3,093	49	38	92	57	0	0	0	0	3,135	3,572	6,537	7,753
Provision				1,375	4,085	2,859	6,223	1,898	803	1,833	3,825	(725)	893	(57)	4,142	659	2,219	1,884	3,091	0	0	0	0	3,207	8,000	6,519	17,281
Ending Balance	$ 70,189	$ 72,309	$ 71,863	$ 26,029	$ 28,559	$ 26,029	$ 28,559	$ 32,490	$ 27,267	$ 32,490	$ 27,267	$ 8,558	$ 12,877	$ 8,558	$ 12,877	$ 3,112	$ 3,160	$ 3,112	$ 3,160	$ 0	$ 0	$ 0	$ 0	$ 70,189	$ 71,863	$ 70,189	$ 71,863

Reduction to the allowance for credit losses related to financing receivables deemed uncollectible.

Name:	onb_FinancingReceivableAllowanceForCreditLossesChargeOffs
Namespace Prefix:	onb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reflects the gross amount charged against earnings during the period as credit losses (bad debt expense) based on review of the loan and lease portfolio and application of the methodology for estimating credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 114
-Paragraph 20

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 7
-Subparagraph d
-Article 9

+ Details

Name:	us-gaap_AllowanceForLoanAndLeaseLossesProvisionForLossGross
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Reflects a reduction in bad debt expense attributable to collections of loans and lease receivables which had previously been fully or partially charged off as bad debts.

+ References

+ Details

Name:	us-gaap_AllowanceForLoanAndLeaseLossesRecoveriesOfBadDebts
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The allowance for loan and lease losses represents the reserve to cover probable credit losses related to specifically identified loans and leases, as well as probable credit losses inherent in the remainder of the loan portfolio as of the balance sheet date. For banks, include currently required allocated transfer risk reserves. Include carryover of or adjustments to the allowance for loan losses in connection with business combinations determined to be appropriate.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher OTS
-Name Federal Regulation (FR)
-Number Title 12
-Chapter V
-Section 563c.102
-Paragraph 8
-Subparagraph a(ii)
-Subsection I

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 6
-Section L
-Subsection 1

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 114
-Paragraph 20

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 7
-Subparagraph d
-Article 9

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 5
-Paragraph 8, 9

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant