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LOANS, Troubled Debt Restructuring (TDR) (Details) (USD $) | 12 Months Ended
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Dec. 31, 2014 Loan | Dec. 31, 2013 Loan
Financing Receivable, Modifications [Line Items] |  |
Individual commercial loan evaluated for impairment, minimum | $ 500,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment |
TDR included in general loan loss allocation and the qualitative review, maximum | 500,000 cbu_FinancingReceivableAllowanceForCreditLossesCollectivelyModifiedEvaluatedForImpairment |
Troubled debt restructurings, nonaccrual, number of loans | 68 cbu_TroubledDebtRestructuringsNonaccrual | 47 cbu_TroubledDebtRestructuringsNonaccrual
Troubled debt restructurings, nonaccrual, amount | 2,752,000 cbu_TroubledDebtRestructuringsNonaccrualAmount | 2,046,000 cbu_TroubledDebtRestructuringsNonaccrualAmount
Troubled debt restructurings, accruing, number of loans | 157 cbu_TroubledDebtRestructuringsAccruing | 213 cbu_TroubledDebtRestructuringsAccruing
Troubled debt restructurings, accruing, amount | 3,200,000 cbu_TroubledDebtRestructuringsAccruingCarryingBalance | 3,389,000 cbu_TroubledDebtRestructuringsAccruingCarryingBalance
Troubled debt restructurings, total, number of loans | 225 cbu_TroubledDebtRestructurings | 260 cbu_TroubledDebtRestructurings
Troubled debt restructurings, total, amount | 5,952,000 us-gaap_FinancingReceivableModificationsRecordedInvestment | 5,435,000 us-gaap_FinancingReceivableModificationsRecordedInvestment
Loans modified in TDR during the year, number of contracts | 82 us-gaap_FinancingReceivableModificationsNumberOfContracts2 | 106 us-gaap_FinancingReceivableModificationsNumberOfContracts2
Loans modified in TDR during the year, amount | 2,201,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 | 2,641,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Number of non-Chapter 7 bankruptcy TDRs | 3 cbu_FinancingReceivableModificationsNonChapter7BankruptcyTDRsNumberOfContracts | 2 cbu_FinancingReceivableModificationsNonChapter7BankruptcyTDRsNumberOfContracts
Consumer Mortgage [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Troubled debt restructurings, nonaccrual, number of loans | 49 cbu_TroubledDebtRestructuringsNonaccrual / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember | 31 cbu_TroubledDebtRestructuringsNonaccrual / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember
Troubled debt restructurings, nonaccrual, amount | 2,092,000 cbu_TroubledDebtRestructuringsNonaccrualAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember | 1,682,000 cbu_TroubledDebtRestructuringsNonaccrualAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember
Troubled debt restructurings, accruing, number of loans | 37 cbu_TroubledDebtRestructuringsAccruing / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember | 48 cbu_TroubledDebtRestructuringsAccruing / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember
Troubled debt restructurings, accruing, amount | 1,770,000 cbu_TroubledDebtRestructuringsAccruingCarryingBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember | 2,171,000 cbu_TroubledDebtRestructuringsAccruingCarryingBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember
Troubled debt restructurings, total, number of loans | 86 cbu_TroubledDebtRestructurings / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember | 79 cbu_TroubledDebtRestructurings / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember
Troubled debt restructurings, total, amount | 3,862,000 us-gaap_FinancingReceivableModificationsRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember | 3,853,000 us-gaap_FinancingReceivableModificationsRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember
Loans modified in TDR during the year, number of contracts | 22 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember | 31 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember
Loans modified in TDR during the year, amount | 949,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember | 1,758,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialMortgageMember
Business Lending [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Troubled debt restructurings, nonaccrual, number of loans | 6 cbu_TroubledDebtRestructuringsNonaccrual / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | 4 cbu_TroubledDebtRestructuringsNonaccrual / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember
Troubled debt restructurings, nonaccrual, amount | 442,000 cbu_TroubledDebtRestructuringsNonaccrualAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | 162,000 cbu_TroubledDebtRestructuringsNonaccrualAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember
Troubled debt restructurings, accruing, number of loans | 3 cbu_TroubledDebtRestructuringsAccruing / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | 1 cbu_TroubledDebtRestructuringsAccruing / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember
Troubled debt restructurings, accruing, amount | 468,000 cbu_TroubledDebtRestructuringsAccruingCarryingBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | 47,000 cbu_TroubledDebtRestructuringsAccruingCarryingBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember
Troubled debt restructurings, total, number of loans | 9 cbu_TroubledDebtRestructurings / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | 5 cbu_TroubledDebtRestructurings / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember
Troubled debt restructurings, total, amount | 910,000 us-gaap_FinancingReceivableModificationsRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | 209,000 us-gaap_FinancingReceivableModificationsRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember
Loans modified in TDR during the year, number of contracts | 7 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | 3 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember
Loans modified in TDR during the year, amount | 769,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | 183,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember
Number of loans restructured via granting a waiver of payments for a period of time | 2 cbu_FinancingReceivableModificationsGrantingAWaiverOfPaymentsForAPeriodOfTimeNumberOfContracts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |
Number of loans restructured by extension of terms | 1 cbu_FinancingReceivableModificationsTermExtensionNumberOfContracts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |
Consumer Indirect [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Troubled debt restructurings, nonaccrual, number of loans | 0 cbu_TroubledDebtRestructuringsNonaccrual / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember | 0 cbu_TroubledDebtRestructuringsNonaccrual / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember
Troubled debt restructurings, nonaccrual, amount | 0 cbu_TroubledDebtRestructuringsNonaccrualAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember | 0 cbu_TroubledDebtRestructuringsNonaccrualAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember
Troubled debt restructurings, accruing, number of loans | 79 cbu_TroubledDebtRestructuringsAccruing / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember | 98 cbu_TroubledDebtRestructuringsAccruing / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember
Troubled debt restructurings, accruing, amount | 615,000 cbu_TroubledDebtRestructuringsAccruingCarryingBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember | 692,000 cbu_TroubledDebtRestructuringsAccruingCarryingBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember
Troubled debt restructurings, total, number of loans | 79 cbu_TroubledDebtRestructurings / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember | 98 cbu_TroubledDebtRestructurings / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember
Troubled debt restructurings, total, amount | 615,000 us-gaap_FinancingReceivableModificationsRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember | 692,000 us-gaap_FinancingReceivableModificationsRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember
Loans modified in TDR during the year, number of contracts | 33 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember | 36 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember
Loans modified in TDR during the year, amount | 312,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember | 327,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentIndirectMember
Consumer Direct [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Troubled debt restructurings, nonaccrual, number of loans | 0 cbu_TroubledDebtRestructuringsNonaccrual / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember | 0 cbu_TroubledDebtRestructuringsNonaccrual / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember
Troubled debt restructurings, nonaccrual, amount | 0 cbu_TroubledDebtRestructuringsNonaccrualAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember | 0 cbu_TroubledDebtRestructuringsNonaccrualAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember
Troubled debt restructurings, accruing, number of loans | 25 cbu_TroubledDebtRestructuringsAccruing / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember | 46 cbu_TroubledDebtRestructuringsAccruing / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember
Troubled debt restructurings, accruing, amount | 69,000 cbu_TroubledDebtRestructuringsAccruingCarryingBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember | 116,000 cbu_TroubledDebtRestructuringsAccruingCarryingBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember
Troubled debt restructurings, total, number of loans | 25 cbu_TroubledDebtRestructurings / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember | 46 cbu_TroubledDebtRestructurings / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember
Troubled debt restructurings, total, amount | 69,000 us-gaap_FinancingReceivableModificationsRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember | 116,000 us-gaap_FinancingReceivableModificationsRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember
Loans modified in TDR during the year, number of contracts | 14 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember | 22 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember
Loans modified in TDR during the year, amount | 26,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember | 75,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_ConsumerInstallmentDirectMember
Home Equity [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Troubled debt restructurings, nonaccrual, number of loans | 13 cbu_TroubledDebtRestructuringsNonaccrual / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember | 12 cbu_TroubledDebtRestructuringsNonaccrual / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember
Troubled debt restructurings, nonaccrual, amount | 218,000 cbu_TroubledDebtRestructuringsNonaccrualAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember | 202,000 cbu_TroubledDebtRestructuringsNonaccrualAmount / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember
Troubled debt restructurings, accruing, number of loans | 13 cbu_TroubledDebtRestructuringsAccruing / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember | 20 cbu_TroubledDebtRestructuringsAccruing / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember
Troubled debt restructurings, accruing, amount | 278,000 cbu_TroubledDebtRestructuringsAccruingCarryingBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember | 363,000 cbu_TroubledDebtRestructuringsAccruingCarryingBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember
Troubled debt restructurings, total, number of loans | 26 cbu_TroubledDebtRestructurings / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember | 32 cbu_TroubledDebtRestructurings / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember
Troubled debt restructurings, total, amount | 496,000 us-gaap_FinancingReceivableModificationsRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember | 565,000 us-gaap_FinancingReceivableModificationsRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember
Loans modified in TDR during the year, number of contracts | 6 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember | 14 us-gaap_FinancingReceivableModificationsNumberOfContracts2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember
Loans modified in TDR during the year, amount | $ 145,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember | $ 298,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cbu_HomeEquityReceivablesMember

X
- Definition The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment and are a TDR. + References No definition available. + Details
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- Definition Number of financing receivables that have been modified by troubled debt restructurings via granting a waiver of payments for a period of time. + References No definition available. + Details
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- Definition Refers to the number of non-Chapter 7 bankruptcy financing receivables that have been modified by troubled debt restructurings during the period. + References No definition available. + Details
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