Name:	cbu_AssumedHealthCareCostTrendRateForParticipantsOlderThan65
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The assumed health care cost trend rate for participants younger than 65 used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

No definition available.

Name:	cbu_AssumedHealthCareCostTrendRateForParticipantsYoungerThan65
Namespace Prefix:	cbu_
Data Type:	num:percentItemType
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The assumed health care cost trend rate for prescription drugs used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

No definition available.

Name:	cbu_AssumedHealthCareCostTrendRateForPrescriptionDrugs
Namespace Prefix:	cbu_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

Name:	us-gaap_DefinedBenefitPlanAssumedHealthCareCostTrendRatesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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The ultimate trend rate for health care costs.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (l)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

Name:	us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
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Year the ultimate health care cost trend rate is expected to be reached, in CCYY format.