Cover	May 09, 2023
Cover [Abstract]
Document Type	8-K
Document Period End Date	May 09, 2023
Entity Registrant Name	ISABELLA BANK CORP
Entity Incorporation, State or Country Code	MI
Entity File Number	000-18415
Entity Tax Identification Number	38-2830092
Entity Address, Address Line One	401 North Main Street
Entity Address, City or Town	Mt. Pleasant
Entity Address, State or Province	MI
Entity Address, Postal Zip Code	48858-1649
City Area Code	989
Local Phone Number	772-9471
Written Communications	false
Soliciting Material	false
Pre-commencement Tender Offer	false
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Entity Emerging Growth Company	false
Entity Central Index Key	0000842517
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Cover page.

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For the EDGAR submission types of Form 8-K: the date of the report, the date of the earliest event reported; for the EDGAR submission types of Form N-1A: the filing date; for all other submission types: the end of the reporting or transition period. The format of the date is YYYY-MM-DD.

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The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word 'Other'.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Commission file number. The field allows up to 17 characters. The prefix may contain 1-3 digits, the sequence number may contain 1-8 digits, the optional suffix may contain 1-4 characters, and the fields are separated with a hyphen.

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Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act.

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Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as soliciting material pursuant to Rule 14a-12 under the Exchange Act.

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Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as written communications pursuant to Rule 425 under the Securities Act.

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