Cover - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Mar. 05, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Document Transition Report	false
Entity File Number	0-18415
Entity Registrant Name	Isabella Bank Corp
Entity Incorporation, State or Country Code	MI
Entity Tax Identification Number	38-2830092
Entity Address, Address Line One	401 North Main Street
Entity Address, City or Town	Mount Pleasant
Entity Address, State or Province	MI
Entity Address, Postal Zip Code	48858
City Area Code	(989)
Local Phone Number	772-9471
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 142,188
Entity Common Stock, Shares Outstanding		7,502,990
Current Fiscal Year End Date	--12-31