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EMPLOYEE BENEFITS - Pension Plan Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Defined Contribution Plan Disclosure [Line Items] |  |  |
Liability | $ 242,463 | $ 1,653,788 |
Expected long-term rate of return | 7.00% | 7.00% |
The Connecticut Light and Power Company |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Liability | $ 26,820 | $ 478,325 |
Public Service Company of New Hampshire |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Liability | 30,184 | 184,715 |
Pension Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Increase in liability due to amendment in pension plan | 286,800 | 603,000 |
Funded status of plan | $ (234,200) | $ (1,636,100) |
Expected long-term rate of return | 8.25% | 8.25% | 8.25%
Pension Plan | The Connecticut Light and Power Company |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Funded status of plan | $ (7,100) | $ (434,200) |
Pension Plan | Public Service Company of New Hampshire |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Funded status of plan | (26,400) | (155,000) |
Other Postretirement Benefits Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Increase in liability due to amendment in pension plan | 29,800 | 68,300 |
Funded status of plan | $ 254,000 | $ 10,200 |
Expected long-term rate of return | 8.25% | 8.25% | 8.25%
Estimated future employer contributions in next fiscal year | $ 2,400 |  |
Other Postretirement Benefits Plan | The Connecticut Light and Power Company |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Funded status of plan | (19,800) | $ (44,500) |
Other Postretirement Benefits Plan | Public Service Company of New Hampshire |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Funded status of plan | (4,300) | (30,100) |
Other Current Liabilities |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Funded status of plan | 9,700 | 6,800 |
Other Long-Term Assets | Other Postretirement Benefits Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Prepaid asset | 272,000 | 34,700 |
Accrued Pension, SERP and PBOP | Other Postretirement Benefits Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Liability | 18,000 | $ 24,500 |
Minimum | Pension Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Estimated future employer contributions in next fiscal year | 100,000 |  |
Maximum | Pension Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Estimated future employer contributions in next fiscal year | $ 175,000 |  |
Pre-65 Plan | Other Postretirement Benefits Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Health care trend rate | 6.50% |  |
Ultimate rate | 5.00% |  |
Pre-65 Plan | Minimum | Other Postretirement Benefits Plan | Aquarion |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Health care trend rate | 3.50% | 3.50% |
Pre-65 Plan | Maximum | Other Postretirement Benefits Plan | Aquarion |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Health care trend rate | 6.20% | 6.50% |
Post-65 Plan | Other Postretirement Benefits Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Ultimate rate | 3.50% |  |
Eversource Service Pension and PBOP Plans |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Assumed rate of return | 8.25% |  |
Aquarion Plans |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Assumed rate of return | 7.00% |  |

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