Schedule of Assets (Held at End of Year) (Details) - Community Financial System, Inc. 401(k) Employee Stock Ownership Plan
|
12 Months Ended |
|
Dec. 31, 2025
USD ($)
shares
|
|---|
| Schedule of Assets (Held at End of Year) |
|
| Participant loans |
$ 4,909,378
|
| Total |
509,337,923
|
| Mutual funds |
|
| Schedule of Assets (Held at End of Year) |
|
| Current Value |
$ 368,463,156
|
| Investment, Identifier [Axis]: Amercent Small Cap Value, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:AmercentSmallCapValueMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
386,954
|
| Current Value |
$ 3,474,848
|
| Investment, Identifier [Axis]: American Funds EuroPacific Growth Fund, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:AmericanFundsEuropacificGrowthFundMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
288,156
|
| Current Value |
$ 17,456,519
|
| Investment, Identifier [Axis]: Charles Schwab IDA Account, Self-Directed Brokerage |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:CharlesSchwabIdaAccountMember
|
| Investment type |
Self-Directed Brokerage
|
| Current Value |
$ 8,046,915
|
| Investment, Identifier [Axis]: Community Financial System, Inc, Common Stock |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:CommunityFinancialSystemIncCommonStockMember
|
| Investment type |
Common stock of plan sponsor
|
| Number of shares | shares |
1,451,117
|
| Current Value |
$ 83,352,180
|
| Investment party in interest |
true
|
| Investment, Identifier [Axis]: DFA Emerging Markets Core Equity, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:DfaEmergingMarketsCoreEquityMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
189,101
|
| Current Value |
$ 5,499,046
|
| Investment, Identifier [Axis]: DFA Real Estate Securities I, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:DfaRealEstateSecuritiesIMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
41,773
|
| Current Value |
$ 1,658,387
|
| Investment, Identifier [Axis]: Federated Total Return Bond Fund, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:FederatedTotalReturnBondFundMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
1,338,590
|
| Current Value |
$ 12,837,082
|
| Investment, Identifier [Axis]: Guggenheim Macro Opportunities Fund, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:GuggenheimMacroOpportunitiesFundMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
165,024
|
| Current Value |
$ 4,130,548
|
| Investment, Identifier [Axis]: HB&T Metlife Stable Value Fund R0, Stable Value Fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:HbTMetlifeStableValueFundR0Member
|
| Investment type |
Stable Value Fund
|
| Number of shares | shares |
2,150,753
|
| Current Value |
$ 30,906,317
|
| Investment party in interest |
true
|
| Investment, Identifier [Axis]: JPMorgan Large Cap Growth Fund, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:JpmorganLargeCapGrowthFundMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
593,728
|
| Current Value |
$ 51,321,820
|
| Investment, Identifier [Axis]: Neuberger Berman Small Cap Growth Trust Fund, Mutual Fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:NeubergerBermanSmallCapGrowthTrustFundMember
|
| Investment type |
us-gaap:DefinedBenefitPlanCommonCollectiveTrustMember
|
| Number of shares | shares |
1,244,962
|
| Current Value |
$ 13,659,977
|
| Investment, Identifier [Axis]: T. Rowe Price Div Mid-Cap Growth Fund I, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:T.RowePriceDivMidCapGrowthFundIMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
239,226
|
| Current Value |
$ 11,262,779
|
| Investment, Identifier [Axis]: T. Rowe Price Mid-Cap Value Fund I, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:T.RowePriceMidCapValueFundIMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
293,027
|
| Current Value |
$ 9,397,387
|
| Investment, Identifier [Axis]: T. Rowe Price Spectrum Conserv Alloc Fund I, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:T.RowePriceSpectrumConservAllocFundIMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
169,494
|
| Current Value |
$ 3,467,840
|
| Investment, Identifier [Axis]: T. Rowe Price Spectrum Mod Alloc Fund I, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:T.RowePriceSpectrumModAllocFundIMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
181,568
|
| Current Value |
$ 4,544,658
|
| Investment, Identifier [Axis]: T. Rowe Price Spectrum Mod Growth Alloc Fund I, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:T.RowePriceSpectrumModGrowthAllocFundIMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
70,434
|
| Current Value |
$ 2,998,360
|
| Investment, Identifier [Axis]: Vanguard Equity Income Admiral, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardEquityIncomeAdmiralMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
260,558
|
| Current Value |
$ 24,208,436
|
| Investment, Identifier [Axis]: Vanguard Institutional Index I, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardInstitutionalIndexIMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
69,878
|
| Current Value |
$ 38,578,660
|
| Investment, Identifier [Axis]: Vanguard Mid-Cap Index I, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardMidCapIndexIMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
158,070
|
| Current Value |
$ 12,547,591
|
| Investment, Identifier [Axis]: Vanguard Small-Cap Index Fund I, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardSmallCapIndexFundIMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
92,335
|
| Current Value |
$ 11,410,799
|
| Investment, Identifier [Axis]: Vanguard Target Retirement 2020, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardTargetRetirement2020Member
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
273,543
|
| Current Value |
$ 7,508,742
|
| Investment, Identifier [Axis]: Vanguard Target Retirement 2025, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardTargetRetirement2025Member
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
783,096
|
| Current Value |
$ 15,622,770
|
| Investment, Identifier [Axis]: Vanguard Target Retirement 2030, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardTargetRetirement2030Member
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
837,935
|
| Current Value |
$ 35,469,781
|
| Investment, Identifier [Axis]: Vanguard Target Retirement 2035, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardTargetRetirement2035Member
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
835,932
|
| Current Value |
$ 22,887,816
|
| Investment, Identifier [Axis]: Vanguard Target Retirement 2040, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardTargetRetirement2040Member
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
361,512
|
| Current Value |
$ 18,057,531
|
| Investment, Identifier [Axis]: Vanguard Target Retirement 2045, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardTargetRetirement2045Member
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
296,465
|
| Current Value |
$ 10,299,196
|
| Investment, Identifier [Axis]: Vanguard Target Retirement 2050, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardTargetRetirement2050Member
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
260,735
|
| Current Value |
$ 15,456,356
|
| Investment, Identifier [Axis]: Vanguard Target Retirement 2055, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardTargetRetirement2055Member
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
96,019
|
| Current Value |
$ 6,352,631
|
| Investment, Identifier [Axis]: Vanguard Target Retirement 2060, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardTargetRetirement2060Member
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
90,858
|
| Current Value |
$ 5,540,507
|
| Investment, Identifier [Axis]: Vanguard Target Retirement 2065, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardTargetRetirement2065Member
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
8,203
|
| Current Value |
$ 328,378
|
| Investment, Identifier [Axis]: Vanguard Target Retirement 2070, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardTargetRetirement2070Member
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
7,852
|
| Current Value |
$ 249,846
|
| Investment, Identifier [Axis]: Vanguard Target Retirement Income, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardTargetRetirementIncomeMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
687,431
|
| Current Value |
$ 9,534,674
|
| Investment, Identifier [Axis]: Vanguard Total Bond Index Admiral, Mutual fund |
|
| Schedule of Assets (Held at End of Year) |
|
| Investment issuer name |
cbu:VanguardTotalBondIndexAdmiralMember
|
| Investment type |
Mutual funds
|
| Number of shares | shares |
650,990
|
| Current Value |
$ 6,360,168
|
| Minimum |
|
| Schedule of Assets (Held at End of Year) |
|
| Participant loans, interest rate |
3.25%
|
| Maximum |
|
| Schedule of Assets (Held at End of Year) |
|
| Participant loans, interest rate |
9.25%
|