SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES -Premises and Equipment and Wealth Management and Group Fee Income (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Property, Plant and Equipment [Line Items]
Assets under management	$ 2,338.0	$ 2,212.0
Chemung Financial Corporation
Property, Plant and Equipment [Line Items]
Assets under management	$ 301.8	$ 301.9
Buildings | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	15 years
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	50 years
Equipment and Furniture | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	3 years
Equipment and Furniture | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives (years)	10 years