Description of the Plan - General (Details) - Community Financial System, Inc. 401(k) Employee Stock Ownership Plan	12 Months Ended
Dec. 31, 2025 age
Description of the Plan
Minimum age for Plan eligibility	18
Minimum service period for Plan eligibility	90 days
Elective contributions on automatic enrollment	4.00%
Maximum
Description of the Plan
Elective contributions on automatic enrollment	8.00%
After 2 years
Description of the Plan
Increase in deferral percentage	2.00%
Thereafter
Description of the Plan
Increase in deferral percentage	2.00%

Represents the minimum age criteria for plan eligibility under (employee benefit plan (EBP)).

No definition available.

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- Definition

Represents the minimum service period for plan eligibility under (employee benefit plan (EBP)).

+ References

No definition available.

+ Details

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- Definition

Percentage of increase in eligible compensation contributed for participant automatically enrolled until changed by employee in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

+ Details

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- Definition

Percentage of eligible compensation contributed for participant automatically enrolled in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478873/962-325-55-17

+ Details

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