v3.26.1
Statements of Net Assets Available for Benefits - Community Financial System, Inc. 401(k) Employee Stock Ownership Plan - USD ($)
Dec. 31, 2025
Dec. 31, 2024
Investments, at fair value/ at net asset value:    
Total investments at fair value/ at NAV $ 473,522,228 $ 437,038,226
Investments, at contract value:    
Stable value fund 30,906,317 32,408,933
Total investments 504,428,545 469,447,159
Receivables:    
Contributions receivable - employer   16,281
Notes receivable from participants, net 4,443,378 4,308,643
Total receivables 4,443,378 4,324,924
Net assets available for benefits 508,871,923 473,772,083
Fair value    
Investments, at fair value/ at net asset value:    
Total investments at fair value/ at NAV 459,862,251 422,168,990
Fair value | Mutual funds    
Investments, at fair value/ at net asset value:    
Total investments at fair value/ at NAV 368,463,156 327,318,655
Fair value | Community Financial System, Inc. common stock    
Investments, at fair value/ at net asset value:    
Total investments at fair value/ at NAV 83,352,180 87,776,467
Fair value | Self-directed brokerage    
Investments, at fair value/ at net asset value:    
Total investments at fair value/ at NAV 8,046,915 7,073,868
NAV    
Investments, at fair value/ at net asset value:    
Total investments at fair value/ at NAV $ 13,659,977 $ 14,869,236
EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value, Type [Extensible Enumeration] us-gaap:DefinedBenefitPlanCommonCollectiveTrustMember us-gaap:DefinedBenefitPlanCommonCollectiveTrustMember