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PENSION AND OTHER BENEFIT PLANS (Tables) | 12 Months Ended
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Dec. 31, 2023
PENSION AND OTHER BENEFIT PLANS |
Schedule of funded status of the company's plans reconciled with amounts reported | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Pension Benefits | ​ | Post-retirement Benefits
(000’s omitted) |  | 2023 |  | 2022 |  | 2023 |  | 2022
Change in benefit obligation: |  | ​ |  |  | ​ |  |  | ​ | ​ |  | ​ |
Benefit obligation at the beginning of year | ​ | $ | 151,361 | ​ | $ | 183,270 | ​ | $ | 1,656 | ​ | $ | 1,529
Service cost | ​ |  | 4,433 | ​ |  | 4,959 | ​ |  | 0 | ​ |  | 0
Interest cost | ​ |  | 7,561 | ​ |  | 5,334 | ​ |  | 92 | ​ |  | 68
Plan amendment / acquisition | ​ |  | 0 | ​ |  | 1,851 | ​ |  | 0 | ​ |  | 536
Participant contributions | ​ |  | 0 | ​ |  | 0 | ​ |  | 0 | ​ |  | 0
Deferred actuarial loss/(gain) | ​ |  | 5,530 | ​ |  | (31,759) | ​ |  | 165 | ​ |  | (306)
Benefits paid | ​ |  | (10,605) | ​ |  | (12,294) | ​ |  | (199) | ​ |  | (171)
Benefit obligation at end of year | ​ |  | 158,280 | ​ |  | 151,361 | ​ |  | 1,714 | ​ |  | 1,656
Change in plan assets: | ​ |  | ​ | ​ |  | ​ | ​ |  | ​ | ​ |  | ​
Fair value of plan assets at beginning of year | ​ |  | 244,332 | ​ |  | 290,687 | ​ |  | 0 | ​ |  | 0
Actual return of plan assets | ​ |  | 28,746 | ​ |  | (34,967) | ​ |  | 0 | ​ |  | 0
Participant contributions | ​ |  | 0 | ​ |  | 0 | ​ |  | 0 | ​ |  | 0
Employer contributions | ​ |  | 4,989 | ​ |  | 906 | ​ |  | 199 | ​ |  | 171
Plan acquisition | ​ |  | 0 | ​ |  | 0 | ​ |  | 0 | ​ |  | 0
Benefits paid | ​ |  | (10,605) | ​ |  | (12,294) | ​ |  | (199) | ​ |  | (171)
Fair value of plan assets at end of year | ​ |  | 267,462 | ​ |  | 244,332 | ​ |  | 0 | ​ |  | 0
Over/(Under) funded status at year end | ​ | $ | 109,182 | ​ | $ | 92,971 | ​ | $ | (1,714) | ​ | $ | (1,656)
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Amounts recognized in the consolidated statement of condition were: | ​ |  |  | ​ |  |  | ​ |  |  | ​ |  |
Other assets | ​ | $ | 123,263 | ​ | $ | 106,986 | ​ | $ | 0 | ​ | $ | 0
Other liabilities | ​ |  | (14,081) | ​ |  | (14,015) | ​ |  | (1,714) | ​ |  | (1,656)
Amounts recognized in accumulated other comprehensive loss/(income) (“AOCI”) were: | ​ |  |  | ​ |  |  | ​ |  |  | ​ |  |
Net loss | ​ | $ | 33,977 | ​ | $ | 38,894 | ​ | $ | 398 | ​ | $ | 255
Net prior service cost (credit) | ​ |  | 2,292 | ​ |  | 3,112 | ​ |  | (549) | ​ |  | (728)
Pre-tax AOCI | ​ |  | 36,269 | ​ |  | 42,006 | ​ |  | (151) | ​ |  | (473)
Taxes | ​ |  | (8,955) | ​ |  | (10,351) | ​ |  | 41 | ​ |  | 119
AOCI at year end | ​ | $ | 27,314 | ​ | $ | 31,655 | ​ | $ | (110) | ​ | $ | (354)
Schedule of amounts recognized in accumulated other comprehensive income, net of tax | Amounts recognized in accumulated other comprehensive income, net of tax, for the year ended December 31, are as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Pension Benefits | ​ | Post-retirement Benefits
(000’s omitted) |  | 2023 |  | 2022 |  | 2023 |  | 2022
Prior service (credit)/cost | ​ | $ | (620) | ​ | $ | (648) | ​ | $ | 135 | ​ | $ | 135
Net (gain) loss | ​ |  | (3,720) | ​ |  | 16,593 | ​ |  | 108 | ​ |  | (249)
Total | ​ | $ | (4,340) | ​ | $ | 15,945 | ​ | $ | 243 | ​ | $ | (114)
​
Schedule of weighted-average assumptions used to determine the benefit obligations | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Pension Benefits | ​ | Post-retirement Benefits |
​ |  | 2023 |  | 2022 |  | 2023 |  | 2022 |
Discount rate |  | 5.20 | % | 5.40 | % | 5.20 | % | 5.40 | %
Expected return on plan assets |  | 7.00 | % | 6.70 | % | N/A |  | N/A | ​
Rate of compensation increase | ​ | 3.50% for 2024 | + | 3.50% for 2024 | + | N/A | ​ | N/A | ​
Interest crediting rates | ​ | 6.00% while employed, | ​ | 6.00% while employed, | ​ | N/A | ​ | N/A | ​
​ | ​ | 4.47% after termination | ​ | 3.55% after termination | ​ | ​ | ​ | ​ | ​
​
Schedule of net periodic benefit cost | The net periodic benefit cost as of December 31 is as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Pension Benefits | ​ | Post-retirement Benefits
(000’s omitted) |  | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Service cost | ​ | $ | 4,433 | ​ | $ | 4,959 | ​ | $ | 5,920 | ​ | $ | 0 | ​ | $ | 0 | ​ | $ | 0
Interest cost | ​ |  | 7,561 | ​ |  | 5,334 | ​ |  | 5,036 | ​ |  | 92 | ​ |  | 68 | ​ |  | 44
Expected return on plan assets | ​ |  | (16,079) | ​ |  | (19,025) | ​ |  | (18,783) | ​ |  | 0 | ​ |  | 0 | ​ |  | 0
Plan amendment | ​ |  | 0 | ​ |  | (556) | ​ |  | 0 | ​ |  | 0 | ​ |  | 0 | ​ |  | 0
Amortization of unrecognized net loss | ​ |  | (2,220) | ​ |  | 842 | ​ |  | 3,600 | ​ |  | 22 | ​ |  | 23 | ​ |  | 45
Amortization of prior service cost | ​ |  | 820 | ​ |  | 615 | ​ |  | 379 | ​ |  | (179) | ​ |  | (179) | ​ |  | (179)
Net periodic benefit | ​ | $ | (5,485) | ​ | $ | (7,831) | ​ | $ | (3,848) | ​ | $ | (65) | ​ | $ | (88) | ​ | $ | (90)
​
Schedule of weighted-average assumptions used to determine the net periodic pension cost | The weighted-average assumptions used to determine the net periodic pension cost for the years ended December 31 are as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Pension Benefits | ​ | Post-retirement Benefits |
​ |  | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021 |
Discount rate |  | 5.40 | % | 3.10 | % | 2.80 | % | 5.40 | % | 3.10 | % | 2.80 | %
Expected return on plan assets |  | 6.70 | % | 6.70 | % | 7.00 | % | N/A |  | N/A |  | N/A | ​
Rate of compensation increase |  | 4.50% for 2023, | ​ | 4.00% for 2022, | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | 3.50% for 2024 | + | 3.50% for 2023 | + | 3.50 | % | N/A | ​ | N/A | ​ | N/A | ​
Interest crediting rates | ​ | 6.00% while employed, | ​ | 6.00% while employed, | ​ | 6.00% while employed, | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | 3.55% after termination | ​ | 1.94% after termination | ​ | 1.42% after termination | ​ | N/A | ​ | N/A | ​ | N/A | ​
Schedule of amount of benefit payments | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | Pension | ​ | ​ | Post-retirement
(000’s omitted) |  | ​ | Benefits |  | ​ | Benefits
2024 | ​ | $ | 13,680 | ​ | $ | 182
2025 | ​ |  | 11,811 | ​ |  | 161
2026 | ​ |  | 13,040 | ​ |  | 158
2027 | ​ |  | 13,065 | ​ |  | 156
2028 | ​ |  | 12,625 | ​ |  | 152
2029-2033 | ​ |  | 66,724 | ​ |  | 690
​
Schedule of fair values of the company's defined benefit pension plan assets | The fair values of the Company’s defined benefit pension plan assets at December 31, 2023 by asset category are as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Quoted Prices | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | in Active | ​ | Significant | ​ | Significant | ​ |  | ​
​ | ​ | Markets for | ​ | Observable | ​ | Unobservable | ​ |  | ​
​ | ​ | Identical Assets | ​ | Inputs | ​ | Inputs | ​ |  | ​
Asset category (000’s omitted) |  | Level 1 |  | Level 2 |  | Level 3 |  | Total
Cash equivalents | ​ | $ | 13,441 | ​ | $ | 0 | ​ | $ | 0 | ​ | $ | 13,441
Equity securities: | ​ |  | ​ | ​ |  | ​ | ​ |  |  | ​ |  | ​
U.S. large-cap | ​ |  | 66,709 | ​ |  | 0 | ​ |  | 0 | ​ |  | 66,709
U.S. mid/small cap | ​ |  | 23,127 | ​ |  | 0 | ​ |  | 0 | ​ |  | 23,127
CBU common stock | ​ |  | 5,691 | ​ |  | 0 | ​ |  | 0 | ​ |  | 5,691
International | ​ |  | 50,270 | ​ |  | 0 | ​ |  | 0 | ​ |  | 50,270
Other | ​ |  | 1,966 | ​ |  | 0 | ​ |  | 0 | ​ |  | 1,966
​ | ​ |  | 147,763 | ​ |  | 0 | ​ |  | 0 | ​ |  | 147,763
​ | ​ |  | ​ | ​ |  | ​ | ​ |  |  | ​ |  | ​
Fixed income securities: | ​ |  | ​ | ​ |  | ​ | ​ |  |  | ​ |  | ​
Government securities | ​ |  | 59,107 | ​ |  | 15,491 | ​ |  | 0 | ​ |  | 74,598
Investment grade bonds | ​ |  | 0 | ​ |  | 17,968 | ​ |  | 0 | ​ |  | 17,968
​ | ​ |  | 59,107 | ​ |  | 33,459 | ​ |  | 0 | ​ |  | 92,566
​ | ​ |  | ​ | ​ |  | ​ | ​ |  |  | ​ |  | ​
Other investments (b) | ​ |  | 12,759 | ​ |  | 0 | ​ |  | 0 | ​ |  | 12,759
​ | ​ |  | ​ | ​ |  | ​ | ​ |  |  | ​ |  | ​
Total (c) | ​ | $ | 233,070 | ​ | $ | 33,459 | ​ | $ | 0 | ​ | $ | 266,529
​ The fair values of the Company’s defined benefit pension plan assets at December 31, 2022 by asset category are as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Quoted Prices | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | in Active | ​ | Significant | ​ | Significant | ​ | ​ | ​
​ | ​ | Markets for | ​ | Observable | ​ | Unobservable | ​ | ​ | ​
​ | ​ | Identical Assets | ​ | Inputs | ​ | Inputs | ​ | ​ | ​
Asset category (000’s omitted) |  | Level 1 |  | Level 2 |  | Level 3 |  | Total
Cash equivalents | ​ | $ | 18,625 | ​ | $ | 0 | ​ | $ | 0 | ​ | $ | 18,625
Equity securities: | ​ |  | ​ | ​ |  | ​ | ​ |  |  | ​ |  | ​
U.S. large-cap | ​ |  | 52,682 | ​ |  | 0 | ​ |  | 0 | ​ |  | 52,682
U.S. mid/small cap | ​ |  | 16,432 | ​ |  | 0 | ​ |  | 0 | ​ |  | 16,432
CBU common stock | ​ |  | 6,427 | ​ |  | 0 | ​ |  | 0 | ​ |  | 6,427
International | ​ |  | 51,725 | ​ |  | 0 | ​ |  | 0 | ​ |  | 51,725
Other | ​ | ​ | 1,273 | ​ | ​ | 0 | ​ | ​ | 0 | ​ | ​ | 1,273
​ | ​ |  | 128,539 | ​ |  | 0 | ​ |  | 0 | ​ |  | 128,539
​ | ​ |  | ​ | ​ |  | ​ | ​ |  |  | ​ |  | ​
Fixed income securities: | ​ |  | ​ | ​ |  | ​ | ​ |  |  | ​ |  | ​
Government securities | ​ |  | 49,665 | ​ |  | 6,897 | ​ |  | 0 | ​ |  | 56,562
Investment grade bonds | ​ |  | 3,648 | ​ |  | 14,854 | ​ |  | 0 | ​ |  | 18,502
High yield(a) | ​ |  | 7,134 | ​ |  | 0 | ​ |  | 0 | ​ |  | 7,134
​ | ​ |  | 60,447 | ​ |  | 21,751 | ​ |  | 0 | ​ |  | 82,198
​ | ​ |  | ​ | ​ |  | ​ | ​ |  |  | ​ |  | ​
Other investments (b) | ​ |  | 14,342 | ​ |  | 0 | ​ |  | 0 | ​ |  | 14,342
​ | ​ |  | ​ | ​ |  | ​ | ​ |  |  | ​ |  | ​
Total (c) | ​ | $ | 221,953 | ​ | $ | 21,751 | ​ | $ | 0 | ​ | $ | 243,704
(a) | This category is exchange-traded funds representing a diversified index of high yield corporate bonds.
(b) | This category is comprised of exchange-traded funds and mutual funds holding non-traditional investment classes including private equity funds and alternative exchange funds.
(c) | Excludes dividends and interest receivable totaling $0.9 million and $0.6 million at December 31, 2023 and 2022, respectively.
​

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