XML 47 R51.htm IDEA: XBRL DOCUMENT
v3.20.1

LOANS, Allowance for Credit Losses (Details) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2020 USD ($) | Mar. 31, 2019 USD ($) | Mar. 31, 2021 USD ($)
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | $ 49,911 | $ 49,284 | $ 55,652
Charge-offs |  | (3,901) |
Recoveries |  | 1,302 |
Provision |  | 2,422 |
Ending balance | 55,652 | 49,107 |
Liabilities for off-balance-sheet credit exposures [Roll Forward] |  |  |
Beginning balance | 0 |  |
Total allowance for credit losses [Roll Forward] |  |  |
Beginning balance | 49,911 |  |
Provision | $ 5,594 | 2,422 |
Allowance for Credit Losses [Abstract] |  |  |
Allowance for credit losses to total loans ratio | 0.0081 |  |
Increase in allowance for credit losses to total loans ratio over the same quarter in prior year | 300.00% |  |
Increase in allowance for credit losses to total loans ratio over the prior year end | 900.00% |  |
Forecast [Member] | Minimum [Member] | COVID-19 [Member] |  |  |
Allowance for Credit Losses [Abstract] |  |  |
Percentage of peak unemployment |  |  | 8.00%
Forecast [Member] | Maximum [Member] | COVID-19 [Member] |  |  |
Allowance for Credit Losses [Abstract] |  |  |
Percentage of peak unemployment |  |  | 13.00%
ASU 2016-13 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | $ 51,268 |  | $ 55,652
Charge-offs | (3,047) |  |
Recoveries | 1,497 |  |
Provision | 5,934 |  |
Ending balance | 55,652 |  |
Liabilities for off-balance-sheet credit exposures [Roll Forward] |  |  |
Beginning balance | 1,185 |  | 845
Charge-offs | 0 |  |
Recoveries | 0 |  |
Provision | (340) |  |
Ending balance | 845 |  |
Total allowance for credit losses [Roll Forward] |  |  |
Beginning balance | 52,453 |  | 56,497
Charge-offs | (3,047) |  |
Recoveries | 1,497 |  |
Provision | 5,594 |  |
Ending balance | 56,497 |  |
ASU 2016-13 [Member] | Impact of ASC 326 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 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 |  |
Purchased Credit Impaired [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 163 | 33 |
Charge-offs |  | 0 |
Recoveries |  | 0 |
Provision |  | 122 |
Ending balance |  | 155 |
Purchased Credit Impaired [Member] | ASU 2016-13 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 0 |  | 0
Charge-offs | 0 |  |
Recoveries | 0 |  |
Provision | 0 |  |
Ending balance | 0 |  |
Purchased Credit Impaired [Member] | ASU 2016-13 [Member] | Impact of ASC 326 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | (163) |  |
Purchased Credit Deteriorated [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 0 |  |
Purchased Credit Deteriorated [Member] | ASU 2016-13 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 3,072 |  | 3,046
Charge-offs | 0 |  |
Recoveries | 0 |  |
Provision | (26) |  |
Ending balance | 3,046 |  |
Purchased Credit Deteriorated [Member] | ASU 2016-13 [Member] | Impact of ASC 326 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 3,072 |  |
Commercial Portfolio Segment [Member] | Business Lending [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 19,426 | 18,522 |
Charge-offs |  | (1,216) |
Recoveries |  | 134 |
Provision |  | 831 |
Ending balance |  | 18,271 |
Commercial Portfolio Segment [Member] | Business Lending [Member] | ASU 2016-13 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 19,714 |  | 19,489
Charge-offs | (176) |  |
Recoveries | 138 |  |
Provision | (187) |  |
Ending balance | 19,489 |  |
Commercial Portfolio Segment [Member] | Business Lending [Member] | ASU 2016-13 [Member] | Impact of ASC 326 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 288 |  |
Residential Portfolio Segment [Member] | Consumer Mortgage [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 10,269 | 10,124 |
Charge-offs |  | (253) |
Recoveries |  | 22 |
Provision |  | 424 |
Ending balance |  | 10,317 |
Residential Portfolio Segment [Member] | Consumer Mortgage [Member] | ASU 2016-13 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 9,218 |  | 12,430
Charge-offs | (186) |  |
Recoveries | 8 |  |
Provision | 3,390 |  |
Ending balance | 12,430 |  |
Residential Portfolio Segment [Member] | Consumer Mortgage [Member] | ASU 2016-13 [Member] | Impact of ASC 326 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | (1,051) |  |
Consumer Portfolio Segment [Member] | Consumer Indirect [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 13,712 | 14,366 |
Charge-offs |  | (1,823) |
Recoveries |  | 962 |
Provision |  | 746 |
Ending balance |  | 14,251 |
Consumer Portfolio Segment [Member] | Consumer Indirect [Member] | ASU 2016-13 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 12,715 |  | 13,694
Charge-offs | (2,079) |  |
Recoveries | 1,163 |  |
Provision | 1,895 |  |
Ending balance | 13,694 |  |
Consumer Portfolio Segment [Member] | Consumer Indirect [Member] | ASU 2016-13 [Member] | Impact of ASC 326 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | (997) |  |
Consumer Portfolio Segment [Member] | Consumer Direct [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 3,255 | 3,095 |
Charge-offs |  | (535) |
Recoveries |  | 179 |
Provision |  | 317 |
Ending balance |  | 3,056 |
Consumer Portfolio Segment [Member] | Consumer Direct [Member] | ASU 2016-13 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 2,612 |  | 3,737
Charge-offs | (533) |  |
Recoveries | 182 |  |
Provision | 1,476 |  |
Ending balance | 3,737 |  |
Consumer Portfolio Segment [Member] | Consumer Direct [Member] | ASU 2016-13 [Member] | Impact of ASC 326 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | (643) |  |
Consumer Portfolio Segment [Member] | Home Equity [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 2,129 | 2,144 |
Charge-offs |  | (74) |
Recoveries |  | 5 |
Provision |  | (8) |
Ending balance |  | 2,067 |
Consumer Portfolio Segment [Member] | Home Equity [Member] | ASU 2016-13 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 2,937 |  | 2,484
Charge-offs | (73) |  |
Recoveries | 6 |  |
Provision | (386) |  |
Ending balance | 2,484 |  |
Consumer Portfolio Segment [Member] | Home Equity [Member] | ASU 2016-13 [Member] | Impact of ASC 326 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 808 |  |
Unallocated Financing Receivables [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 957 | 1,000 |
Charge-offs |  | 0 |
Recoveries |  | 0 |
Provision |  | (10) |
Ending balance |  | $ 990 |
Unallocated Financing Receivables [Member] | ASU 2016-13 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | 1,000 |  | $ 772
Charge-offs | 0 |  |
Recoveries | 0 |  |
Provision | (228) |  |
Ending balance | 772 |  |
Unallocated Financing Receivables [Member] | ASU 2016-13 [Member] | Impact of ASC 326 [Member] |  |  |
Allowance for credit losses - loans [Roll Forward] |  |  |
Beginning balance | $ 43 |  |

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

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 Increase (Decrease) in allowance for credit losses to total loans ratio over prior year end. + References No definition available. + Details
Name: | cbu_IncreaseDecreaseInAllowanceForCreditLossesToTotalLoansRatioOverPriorYearEnd
Namespace Prefix: | cbu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Increase (Decrease) in allowance for credit losses to total loans ratio over the same quarter in prior year. + References No definition available. + Details
Name: | cbu_IncreaseDecreaseInAllowanceForCreditLossesToTotalLoansRatioOverTheSameQuarterInPriorYear
Namespace Prefix: | cbu_
Data Type: | num:percentItemType
Balance Type: | na
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 Percentage of peak unemployment due to decrease in economic activity. + References No definition available. + Details
Name: | cbu_PercentageOfUnemployment
Namespace Prefix: | cbu_
Data Type: | num:percentItemType
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=118936363&loc=SL6953423-111524 + Details
Name: | us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
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=118936363&loc=SL6953423-111524 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + 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=118936363&loc=SL6953423-111524 Reference 2: 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=118955202&loc=SL82895884-210446 Reference 3: 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=119407570&loc=SL82919249-210447 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(7)(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 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=119407570&loc=SL82919249-210447 + Details
Name: | us-gaap_FinancingReceivableAllowanceForCreditLosses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of recovery of financing receivables doubtful of collection that were previously charged off. + 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=118955255&loc=SL82922352-210448 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(7)(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: 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=119407570&loc=SL82919249-210447 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)(4) -URI http://asc.fasb.org/extlink&oid=118936363&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=119407570&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=118936363&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=118955255&loc=SL82922352-210448 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(7)(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 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=118936363&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=118939070&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=118936363&loc=SL6953423-111524 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -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=27010918&loc=d3e74567-122707 + 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=118956080&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=118955202&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=119407570&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
- Definition Amount of expense related to estimated loss from loan and lease transactions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.11) -URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260 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)(2) -URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524 + Details
Name: | us-gaap_ProvisionForLoanAndLeaseLosses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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 based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value. + 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)(2) -URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.11) -URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585 + Details
Name: | us-gaap_ProvisionForLoanLeaseAndOtherLosses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_UnusualOrInfrequentItemAxis=us-gaap_NaturalDisastersAndOtherCasualtyEventsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | srt_RestatementAxis=srt_RestatementAdjustmentMember
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_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
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: |