XML 36 R40.htm IDEA: XBRL DOCUMENT v2.4.1.9
LOANS, Amount of Business Lending Loans by Credit Quality Category (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]    
Loans $ 4,163,911us-gaap_LoansAndLeasesReceivableGrossCarryingAmount $ 4,236,206us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 3,901,256us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember		 3,963,398us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 262,655us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember		 272,808us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
Business Lending [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 1,239,529us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember		 1,262,484us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
Business Lending [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 1,106,728us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember		 1,124,594us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
Business Lending [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 132,801us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember		 137,890us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
Business Lending [Member] | Pass [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 1,026,896us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 1,043,470us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Business Lending [Member] | Pass [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 936,556us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 949,960us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Business Lending [Member] | Pass [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 90,340us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 93,510us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Business Lending [Member] | Special Mention [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 117,292us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 121,214us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Business Lending [Member] | Special Mention [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 100,507us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 103,176us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Business Lending [Member] | Special Mention [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 16,785us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 18,038us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Business Lending [Member] | Classified [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 90,061us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 92,488us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Business Lending [Member] | Classified [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 69,665us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 71,458us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Business Lending [Member] | Classified [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 20,396us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 21,030us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Business Lending [Member] | Doubtful [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember		 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember
Business Lending [Member] | Doubtful [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember		 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember
Business Lending [Member] | Doubtful [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember		 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember
Business Lending [Member] | Acquired Impaired [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 5,280us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= cbu_PurchasedImpairedMember		 5,312us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= cbu_PurchasedImpairedMember
Business Lending [Member] | Acquired Impaired [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= cbu_PurchasedImpairedMember		 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= cbu_PurchasedImpairedMember
Business Lending [Member] | Acquired Impaired [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 5,280us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= cbu_PurchasedImpairedMember		 5,312us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_InternalCreditAssessmentAxis
= cbu_PurchasedImpairedMember
All Other Loans [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 2,794,528us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbu_AllOtherLoansMember		 2,838,804us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbu_AllOtherLoansMember
All Other Loans [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 129,854us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbu_AllOtherLoansMember		 134,918us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbu_AllOtherLoansMember
All Other Loans [Member] | Performing [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 2,777,746us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbu_AllOtherLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PerformingFinancingReceivableMember		 2,820,941us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbu_AllOtherLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PerformingFinancingReceivableMember
All Other Loans [Member] | Performing [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 127,074us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbu_AllOtherLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PerformingFinancingReceivableMember		 132,074us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbu_AllOtherLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PerformingFinancingReceivableMember
All Other Loans [Member] | Nonperforming [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 16,782us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbu_AllOtherLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember		 17,863us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbu_AllOtherLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember
All Other Loans [Member] | Nonperforming [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 2,780us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbu_AllOtherLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember		 2,844us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cbu_AllOtherLoansMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember
Consumer Mortgage [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 1,605,019us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember		 1,613,384us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
Consumer Mortgage [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 1,538,541us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember		 1,544,401us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
Consumer Mortgage [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 66,478us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember		 68,983us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
Consumer Mortgage [Member] | Performing [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 1,523,969us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PerformingFinancingReceivableMember		 1,529,035us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PerformingFinancingReceivableMember
Consumer Mortgage [Member] | Performing [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 64,294us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PerformingFinancingReceivableMember		 66,629us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PerformingFinancingReceivableMember
Consumer Mortgage [Member] | Nonperforming [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 14,572us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember		 15,366us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= cbu_LegacyLoanMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember
Consumer Mortgage [Member] | Nonperforming [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 2,184us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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Consumer Indirect [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 804,300us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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Consumer Indirect [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 803,362us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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Consumer Indirect [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 938us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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Consumer Indirect [Member] | Performing [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 803,311us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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Consumer Indirect [Member] | Performing [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 938us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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Consumer Indirect [Member] | Nonperforming [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 51us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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Consumer Indirect [Member] | Nonperforming [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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Consumer Direct [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 176,084us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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Consumer Direct [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
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Consumer Direct [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 4,914us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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Consumer Direct [Member] | Performing [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 171,139us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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Consumer Direct [Member] | Performing [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 4,896us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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Consumer Direct [Member] | Nonperforming [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 31us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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Consumer Direct [Member] | Nonperforming [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
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Home Equity [Member]    
Financing Receivable, Recorded Investment [Line Items]    
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Home Equity [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
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Home Equity [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
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Home Equity [Member] | Performing [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
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Home Equity [Member] | Performing [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 56,946us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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Home Equity [Member] | Nonperforming [Member] | Legacy Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans 2,128us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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Home Equity [Member] | Nonperforming [Member] | Acquired Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Loans $ 578us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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