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v2.4.1.9

BORROWINGS (Details) (USD $) | 12 Months Ended | 1 Months Ended | 6 Months Ended
--- | --- | --- | ---
Dec. 31, 2014 Subsidiary | Dec. 31, 2013 | Dec. 31, 2013 | Jun. 30, 2013
Total outstanding borrowings [Abstract] |  |  |  |
Carrying value | $ 440,122,000 us-gaap_BorrowedFunds | $ 244,010,000 us-gaap_BorrowedFunds | $ 244,010,000 us-gaap_BorrowedFunds |
Subordinated debt held by unconsolidated subsidiary trust, discount | 405,000 us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet | 430,000 us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet | 430,000 us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet |
Weighted-average interest rate on borrowings (in hundredths) | 0.89%us-gaap_DebtInstrumentInterestRateDuringPeriod | 2.70%us-gaap_DebtInstrumentInterestRateDuringPeriod |  |
Borrowings by contractual maturity date [Abstract] |  |  |  |
Carrying value | 440,122,000 us-gaap_BorrowedFunds | 244,010,000 us-gaap_BorrowedFunds | 244,010,000 us-gaap_BorrowedFunds |
Weighted Average Interest Rate (in hundredths) | 0.79%us-gaap_LongtermDebtWeightedAverageInterestRate |  |  |
Number of wholly owned, unconsolidated subsidiary trusts | 2 cbu_NumberOfWhollyOwnedUnconsolidatedSubsidiaryTrusts |  |  |
Percent ownership of unconsolidated subsidiary trusts (in hundredths) | 100.00%us-gaap_EquityMethodInvestmentOwnershipPercentage |  |  |
Federal Home Loan Bank Overnight Advance [Member] |  |  |  |
Total outstanding borrowings [Abstract] |  |  |  |
Carrying value | 338,000,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = cbu_FederalHomeLoanBankOvernightAdvanceMember | 141,900,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = cbu_FederalHomeLoanBankOvernightAdvanceMember | 141,900,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = cbu_FederalHomeLoanBankOvernightAdvanceMember |
Borrowings by contractual maturity date [Abstract] |  |  |  |
Carrying value | 338,000,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = cbu_FederalHomeLoanBankOvernightAdvanceMember | 141,900,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = cbu_FederalHomeLoanBankOvernightAdvanceMember | 141,900,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = cbu_FederalHomeLoanBankOvernightAdvanceMember |
Federal Home Loan Bank Term Advances [Member] |  |  |  |
Total outstanding borrowings [Abstract] |  |  |  |
Debt retirement |  |  | 226,400,000 us-gaap_ExtinguishmentOfDebtAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_FederalHomeLoanBankAdvancesMember | 501,600,000 us-gaap_ExtinguishmentOfDebtAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_FederalHomeLoanBankAdvancesMember
Early extinguishments costs |  |  | 23,800,000 us-gaap_PaymentsOfDebtExtinguishmentCosts / us-gaap_LongtermDebtTypeAxis = us-gaap_FederalHomeLoanBankAdvancesMember | 63,500,000 us-gaap_PaymentsOfDebtExtinguishmentCosts / us-gaap_LongtermDebtTypeAxis = us-gaap_FederalHomeLoanBankAdvancesMember
Community Statutory Trust III [Member] |  |  |  |
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust [Abstract] |  |  |  |
Issuance Date | Jul. 31, 2001 |  |  |
Par Amount | 24,500,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_LongtermDebtTypeAxis = cbu_CommunityStatutoryTrustIiiMember |  |  |
Variable Interest Rate Basis | 3 month LIBOR |  |  |
Variable Interest Rate, Basis Spread (in hundredths) | 3.58%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / us-gaap_LongtermDebtTypeAxis = cbu_CommunityStatutoryTrustIiiMember |  |  |
Effective Interest Rate (in hundredths) | 3.81%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_LongtermDebtTypeAxis = cbu_CommunityStatutoryTrustIiiMember |  |  |
Maturity Date | Jul. 31, 2031 |  |  |
Call Price | Par |  |  |
Community Capital Trust IV [Member] |  |  |  |
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust [Abstract] |  |  |  |
Issuance Date | Dec. 08, 2006 |  |  |
Par Amount | 75,000,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_LongtermDebtTypeAxis = cbu_CommunityCapitalTrustIvMember |  |  |
Variable Interest Rate Basis | 3 month LIBOR |  |  |
Variable Interest Rate, Basis Spread (in hundredths) | 1.65%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / us-gaap_LongtermDebtTypeAxis = cbu_CommunityCapitalTrustIvMember |  |  |
Effective Interest Rate (in hundredths) | 1.89%us-gaap_DebtInstrumentInterestRateEffectivePercentage / us-gaap_LongtermDebtTypeAxis = cbu_CommunityCapitalTrustIvMember |  |  |
Maturity Date | Dec. 15, 2036 |  |  |
Call Price | Par |  |  |
Capital Lease Obligations [Member] |  |  |  |
Total outstanding borrowings [Abstract] |  |  |  |
Carrying value | 0 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = us-gaap_CapitalLeaseObligationsMember | 13,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = us-gaap_CapitalLeaseObligationsMember | 13,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = us-gaap_CapitalLeaseObligationsMember |
Borrowings by contractual maturity date [Abstract] |  |  |  |
Carrying value | 0 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = us-gaap_CapitalLeaseObligationsMember | 13,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = us-gaap_CapitalLeaseObligationsMember | 13,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = us-gaap_CapitalLeaseObligationsMember |
Subordinated Debt Held By Unconsolidated Subsidiary Trust [Member] |  |  |  |
Total outstanding borrowings [Abstract] |  |  |  |
Carrying value | 102,122,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = cbu_SubordinatedDebtHeldByUnconsolidatedSubsidiaryTrustMember | 102,097,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = cbu_SubordinatedDebtHeldByUnconsolidatedSubsidiaryTrustMember | 102,097,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = cbu_SubordinatedDebtHeldByUnconsolidatedSubsidiaryTrustMember |
Borrowings by contractual maturity date [Abstract] |  |  |  |
Carrying value | 102,122,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = cbu_SubordinatedDebtHeldByUnconsolidatedSubsidiaryTrustMember | 102,097,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = cbu_SubordinatedDebtHeldByUnconsolidatedSubsidiaryTrustMember | 102,097,000 us-gaap_BorrowedFunds / us-gaap_LongtermDebtTypeAxis = cbu_SubordinatedDebtHeldByUnconsolidatedSubsidiaryTrustMember |
January 2, 2015 [Member] | Federal Home Loan Bank Overnight Advance [Member] |  |  |  |
Total outstanding borrowings [Abstract] |  |  |  |
Carrying value | 338,000,000 us-gaap_BorrowedFunds / cbu_DebtInstrumentContractualMaturityDateAxis = cbu_ContractualMaturityDateOneMember / us-gaap_LongtermDebtTypeAxis = cbu_FederalHomeLoanBankOvernightAdvanceMember |  |  |
Borrowings by contractual maturity date [Abstract] |  |  |  |
Carrying value | 338,000,000 us-gaap_BorrowedFunds / cbu_DebtInstrumentContractualMaturityDateAxis = cbu_ContractualMaturityDateOneMember / us-gaap_LongtermDebtTypeAxis = cbu_FederalHomeLoanBankOvernightAdvanceMember |  |  |
Weighted Average Interest Rate (in hundredths) | 0.32%us-gaap_LongtermDebtWeightedAverageInterestRate / cbu_DebtInstrumentContractualMaturityDateAxis = cbu_ContractualMaturityDateOneMember / us-gaap_LongtermDebtTypeAxis = cbu_FederalHomeLoanBankOvernightAdvanceMember |  |  |
July 31, 2031 [Member] | Subordinated Debt Held By Unconsolidated Subsidiary Trust [Member] |  |  |  |
Total outstanding borrowings [Abstract] |  |  |  |
Carrying value | 24,802,000 us-gaap_BorrowedFunds / cbu_DebtInstrumentContractualMaturityDateAxis = cbu_ContractualMaturityDateTwoMember / us-gaap_LongtermDebtTypeAxis = cbu_SubordinatedDebtHeldByUnconsolidatedSubsidiaryTrustMember |  |  |
Borrowings by contractual maturity date [Abstract] |  |  |  |
Carrying value | 24,802,000 us-gaap_BorrowedFunds / cbu_DebtInstrumentContractualMaturityDateAxis = cbu_ContractualMaturityDateTwoMember / us-gaap_LongtermDebtTypeAxis = cbu_SubordinatedDebtHeldByUnconsolidatedSubsidiaryTrustMember |  |  |
Weighted Average Interest Rate (in hundredths) | 3.81%us-gaap_LongtermDebtWeightedAverageInterestRate / cbu_DebtInstrumentContractualMaturityDateAxis = cbu_ContractualMaturityDateTwoMember / us-gaap_LongtermDebtTypeAxis = cbu_SubordinatedDebtHeldByUnconsolidatedSubsidiaryTrustMember |  |  |
December 15, 2036 [Member] | Subordinated Debt Held By Unconsolidated Subsidiary Trust [Member] |  |  |  |
Total outstanding borrowings [Abstract] |  |  |  |
Carrying value | 77,320,000 us-gaap_BorrowedFunds / cbu_DebtInstrumentContractualMaturityDateAxis = cbu_ContractualMaturityDateThreeMember / us-gaap_LongtermDebtTypeAxis = cbu_SubordinatedDebtHeldByUnconsolidatedSubsidiaryTrustMember |  |  |
Borrowings by contractual maturity date [Abstract] |  |  |  |
Carrying value | $ 77,320,000 us-gaap_BorrowedFunds / cbu_DebtInstrumentContractualMaturityDateAxis = cbu_ContractualMaturityDateThreeMember / us-gaap_LongtermDebtTypeAxis = cbu_SubordinatedDebtHeldByUnconsolidatedSubsidiaryTrustMember |  |  |
Weighted Average Interest Rate (in hundredths) | 1.89%us-gaap_LongtermDebtWeightedAverageInterestRate / cbu_DebtInstrumentContractualMaturityDateAxis = cbu_ContractualMaturityDateThreeMember / us-gaap_LongtermDebtTypeAxis = cbu_SubordinatedDebtHeldByUnconsolidatedSubsidiaryTrustMember |  |  |

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