XML 86 R71.htm IDEA: XBRL DOCUMENT
v3.22.0.1

LOANS - Allowance for Credit Losses (Details) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($)
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | $ 60,869 | $ 49,911
Charge-offs | (8,965) |
Recoveries | 6,118 |
Provision | (8,153) |
Balance, end of period | 49,869 | 60,869
Liabilities for off-balance-sheet credit exposures [Roll Forward] |  |
Beginning balance | 1,489 | 0
Charge-offs | 0 |
Recoveries | 0 |
Provision | (686) |
Ending balance | 803 | 1,489
Total allowance for credit losses [Roll Forward] |  |
Beginning balance | 62,358 | 49,911
Charge-offs | (8,965) |
Recoveries | 6,118 |
Provision | (8,839) |
Ending balance | $ 50,672 | $ 62,358
Allowance for Credit Losses |  |
Allowance for credit losses to total loans ratio | 0.68 |
Basis points lower level |  | 0.14
Accrued interest and fees receivable | $ 16,700 | $ 22,200
Topic ASC 326 [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | 60,869 | 51,268
Charge-offs |  | (10,664)
Recoveries |  | 5,689
Steuben acquisition |  | 3,662
Provision |  | 10,914
Balance, end of period |  | 60,869
Liabilities for off-balance-sheet credit exposures [Roll Forward] |  |
Beginning balance | 1,489 | 1,185
Charge-offs |  | 0
Recoveries |  | 0
Steuben acquisition |  | 67
Provision |  | 237
Ending balance |  | 1,489
Total allowance for credit losses [Roll Forward] |  |
Beginning balance | 62,358 | 52,453
Charge-offs |  | (10,664)
Recoveries |  | 5,689
Steuben acquisition |  | 3,729
Provision |  | 11,151
Ending balance |  | 62,358
Topic ASC 326 [Member] | Cumulative Effect Adjustment [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period |  | (1,357)
Liabilities for off-balance-sheet credit exposures [Roll Forward] |  |
Beginning balance |  | 1,185
Total allowance for credit losses [Roll Forward] |  |
Beginning balance |  | 2,542
Acquired Impaired Loans [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | 1,882 | 163
Charge-offs | (304) |
Recoveries | 107 |
Provision | 289 |
Balance, end of period | 1,974 | 1,882
Acquired Impaired Loans [Member] | Topic ASC 326 [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | 0 | 0
Charge-offs |  | 0
Recoveries |  | 0
Steuben acquisition |  | 0
Provision |  | 0
Balance, end of period |  | 0
Acquired Impaired Loans [Member] | Topic ASC 326 [Member] | Cumulative Effect Adjustment [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period |  | 163
PCD Loans [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period |  | 0
PCD Loans [Member] | Topic ASC 326 [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | 1,882 | 3,072
Charge-offs |  | (91)
Recoveries |  | 440
Steuben acquisition |  | 668
Provision |  | (2,207)
Balance, end of period |  | 1,882
PCD Loans [Member] | Topic ASC 326 [Member] | Cumulative Effect Adjustment [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period |  | (3,072)
Commercial Portfolio Segment | Business Lending |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period |  | 19,426
Commercial Portfolio Segment | Business Lending | Topic ASC 326 [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | 28,190 | 19,714
Charge-offs |  | (1,497)
Recoveries |  | 356
Steuben acquisition |  | 2,343
Balance, end of period |  | 28,190
Commercial Portfolio Segment | Business Lending | Topic ASC 326 [Member] | Cumulative Effect Adjustment [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period |  | 288
Commercial Portfolio Segment | Consumer Mortgage |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period |  | 10,269
Commercial Portfolio Segment | Consumer Mortgage | Topic ASC 326 [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | 10,672 | 9,218
Charge-offs |  | (862)
Recoveries |  | 130
Steuben acquisition |  | 146
Provision |  | 2,040
Balance, end of period |  | 10,672
Commercial Portfolio Segment | Consumer Mortgage | Topic ASC 326 [Member] | Cumulative Effect Adjustment [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period |  | 1,051
Consumer Portfolio Segment | Business Lending |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | 28,190 |
Charge-offs | (1,618) |
Recoveries | 689 |
Provision | (6,240) |
Balance, end of period | 21,021 | 28,190
Consumer Portfolio Segment | Consumer Mortgage |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | 10,672 |
Charge-offs | (426) |
Recoveries | 91 |
Provision | (320) |
Balance, end of period | 10,017 | 10,672
Consumer Portfolio Segment | Consumer Indirect |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | 13,696 | 13,712
Charge-offs | (5,160) |
Recoveries | 4,346 |
Provision | (1,145) |
Balance, end of period | 11,737 | 13,696
Consumer Portfolio Segment | Consumer Indirect | Topic ASC 326 [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | 13,696 | 12,715
Charge-offs |  | (6,382)
Recoveries |  | 3,992
Steuben acquisition |  | 183
Provision |  | 3,188
Balance, end of period |  | 13,696
Consumer Portfolio Segment | Consumer Indirect | Topic ASC 326 [Member] | Cumulative Effect Adjustment [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period |  | 997
Consumer Portfolio Segment | Consumer Direct |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | 3,207 | 3,255
Charge-offs | (1,232) |
Recoveries | 793 |
Provision | (462) |
Balance, end of period | 2,306 | 3,207
Consumer Portfolio Segment | Consumer Direct | Topic ASC 326 [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | 3,207 | 2,612
Charge-offs |  | (1,633)
Recoveries |  | 743
Steuben acquisition |  | 87
Provision |  | 1,398
Balance, end of period |  | 3,207
Consumer Portfolio Segment | Consumer Direct | Topic ASC 326 [Member] | Cumulative Effect Adjustment [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period |  | 643
Consumer Portfolio Segment | Home Equity |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | 2,222 | 2,129
Charge-offs | (225) |
Recoveries | 92 |
Provision | (275) |
Balance, end of period | 1,814 | 2,222
Consumer Portfolio Segment | Home Equity | Topic ASC 326 [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | 2,222 | 2,937
Charge-offs |  | (199)
Recoveries |  | 28
Steuben acquisition |  | 235
Provision |  | (779)
Balance, end of period |  | 2,222
Consumer Portfolio Segment | Home Equity | Topic ASC 326 [Member] | Cumulative Effect Adjustment [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period |  | (808)
Unallocated Financing Receivables [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | 1,000 | 957
Charge-offs | 0 |
Recoveries | 0 |
Provision | 0 |
Balance, end of period | 1,000 | 1,000
Unallocated Financing Receivables [Member] | Topic ASC 326 [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period | $ 1,000 | 1,000
Charge-offs |  | 0
Recoveries |  | 0
Steuben acquisition |  | 0
Provision |  | 0
Balance, end of period |  | 1,000
Unallocated Financing Receivables [Member] | Topic ASC 326 [Member] | Cumulative Effect Adjustment [Member] |  |
Allowance for credit losses - loans [Roll Forward] |  |
Balance, beginning of period |  | $ (43)

X
- Definition Ratio of allowance for credit losses to total loans. + References No definition available. + Details
Name: | cbu_AllowanceForCreditLossesToTotalLoansRatio
Namespace Prefix: | cbu_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the basis points of total loans ratio that are lower than level. + References No definition available. + Details
Name: | cbu_AllowanceForCreditLossesToTotalLoansRatioBasisSpreadLowerThanLevel
Namespace Prefix: | cbu_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of increase in allowance for credit loss on financing receivable from acquisition. + References No definition available. + Details
Name: | cbu_FinancingReceivableAllowanceForCreditLossAcquisition
Namespace Prefix: | cbu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of acquisition of off-balance sheet credit exposure which had previously been fully or partially written-off. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging. + References No definition available. + Details
Name: | cbu_OffBalanceSheetCreditLossLiabilityAcquisition
Namespace Prefix: | cbu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount that has been written off for expected credit loss for off-balance sheet credit exposure. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging. + References No definition available. + Details
Name: | cbu_OffBalanceSheetCreditLossLiabilityChargeOffs
Namespace Prefix: | cbu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of recovery of off-balance sheet credit exposure which had previously been fully or partially written-off. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging. + References No definition available. + Details
Name: | cbu_OffBalanceSheetCreditLossLiabilityRecovery
Namespace Prefix: | cbu_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss, excluding acquisition-related provision for credit losses based on assessment of uncollectible from the counterparty to reduce the account to their net realizable value. + References No definition available. + Details
Name: | cbu_ProvisionForLoanLeaseAndOtherLossesExcludingAcquisitionRelatedProvisionForCreditLosses
Namespace Prefix: | cbu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of expense related to estimated provision for losses before adjustment. + References No definition available. + Details
Name: | cbu_ProvisionForLossesBeforeAdjustment
Namespace Prefix: | cbu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition For an unclassified balance sheet, the amount of fees and other revenue, excluding investment income receivable, earned but not yet received, which were recognized in conformity with revenue recognition criteria based on estimates or specific contractual terms. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.3) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_AccruedFeesAndOtherRevenueReceivable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_AllowanceForCreditLossAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(4) -URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524 + Details
Name: | us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of addition to allowance reserve for credit loss arising from purchase of loan and lease portfolios. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5212-111524 + Details
Name: | us-gaap_AllowanceForLoanAndLeaseLossesLoansAcquired
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | us-gaap_AllowanceForLoanAndLeaseLossesRollForward
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524 + Details
Name: | us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(7)(2)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Regulation S-K (SK) -Number 229 -Section 1405 -Paragraph (a) -Subparagraph (3) Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Regulation S-K (SK) -Number 229 -Section 1405 -Paragraph (c) Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Regulation S-K (SK) -Number 229 -Section 1405 -Paragraph (a) -Subparagraph (1) + Details
Name: | us-gaap_FinancingReceivableAllowanceForCreditLosses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of increase in allowance for credit loss on financing receivable from recovery. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(4) -URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524 + Details
Name: | us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of writeoff of financing receivable, charged against allowance for credit loss. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448 + Details
Name: | us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SAB Topic 6.L.1) -URI http://asc.fasb.org/extlink&oid=122038336&loc=d3e74567-122707 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (b)(1)(ii) -URI http://asc.fasb.org/extlink&oid=121614798&loc=d3e15032-111544 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524 + Details
Name: | us-gaap_LoansAndLeasesReceivableAllowance
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121611286&loc=d3e11927-110247 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82919202-210446 + Details
Name: | us-gaap_OffBalanceSheetCreditLossLiability
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of expense (reversal of expense) for expected credit loss for off-balance sheet credit exposure. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 + Details
Name: | us-gaap_OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversal
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_OffBalanceSheetCreditLossLiabilityRollforward
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201613Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CumulativeEffectPeriodOfAdoptionAxis=srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CreditLossStatusAxis=cbu_AcquiredImpairedLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CreditLossStatusAxis=us-gaap_FinancialAssetAcquiredWithCreditDeteriorationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbu_ConsumerInstallmentIndirectMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbu_ConsumerInstallmentDirectMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbu_HomeEquityReceivablesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_UnallocatedFinancingReceivablesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |