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EMPLOYEE BENEFITS - Schedule of Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Pension and SERP |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service Cost | $ 44.3 | $ 43.1 | $ 70.1
Interest Cost | 250.0 | 254.0 | 154.5
Expected Return on Plan Assets | (462.6) | (465.0) | (523.6)
Actuarial Loss/(Gain) | 85.9 | 45.8 | 116.0
Prior Service Cost/(Credit) | 1.3 | 1.3 | 1.4
Settlement Loss | 4.3 | 12.4 |
Total Net Periodic Benefit Plan Income | (76.8) | $ (108.4) | $ (181.6)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] |  | Other Income, Net | Other Income, Net
PBOP |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service Cost | 7.0 | $ 7.6 | $ 11.6
Interest Cost | 31.9 | 33.8 | 20.2
Expected Return on Plan Assets | (81.2) | (77.1) | (89.9)
Actuarial Loss/(Gain) | (0.4) | 0.0 | 0.0
Prior Service Cost/(Credit) | (21.6) | (21.6) | (21.7)
Settlement Loss | 0.0 | 0.0 |
Total Net Periodic Benefit Plan Income | $ (64.3) | $ (57.3) | $ (79.8)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] | Other Income, Net | Other Income, Net | Other Income, Net
CL&P | Pension and SERP |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service Cost | $ 12.7 | $ 12.3 | $ 18.7
Interest Cost | 50.3 | 50.5 | 31.3
Expected Return on Plan Assets | (93.5) | (94.2) | (106.3)
Actuarial Loss/(Gain) | 12.1 | 2.5 | 16.2
Prior Service Cost/(Credit) | 0.0 | 0.0 | 0.0
Settlement Loss | 0.0 | 0.0 |
Total Net Periodic Benefit Plan Income | (18.4) | (28.9) | (40.1)
Intercompany Income Allocations | (1.6) | (4.0) | (16.0)
CL&P | PBOP |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service Cost | 1.2 | 1.3 | 2.0
Interest Cost | 5.6 | 6.2 | 3.7
Expected Return on Plan Assets | (9.5) | (9.4) | (11.4)
Actuarial Loss/(Gain) | 0.0 | 0.0 | 0.0
Prior Service Cost/(Credit) | 1.1 | 1.1 | 1.1
Settlement Loss | 0.0 | 0.0 |
Total Net Periodic Benefit Plan Income | (1.6) | (0.8) | (4.6)
Intercompany Income Allocations | (2.2) | (1.9) | (3.7)
NSTAR Electric | Pension and SERP |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service Cost | 7.7 | 7.8 | 13.8
Interest Cost | 51.6 | 53.9 | 32.8
Expected Return on Plan Assets | (112.4) | (113.8) | (128.4)
Actuarial Loss/(Gain) | 25.6 | 17.1 | 32.8
Prior Service Cost/(Credit) | 0.3 | 0.3 | 0.3
Settlement Loss | 0.0 | 0.0 |
Total Net Periodic Benefit Plan Income | (27.2) | (34.7) | (48.7)
Intercompany Income Allocations | (1.3) | (3.0) | (12.4)
NSTAR Electric | PBOP |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service Cost | 1.2 | 1.2 | 2.0
Interest Cost | 8.8 | 9.2 | 5.3
Expected Return on Plan Assets | (39.5) | (36.9) | (42.4)
Actuarial Loss/(Gain) | 0.0 | 0.0 | 0.0
Prior Service Cost/(Credit) | (17.0) | (17.0) | (17.0)
Settlement Loss | 0.0 | 0.0 |
Total Net Periodic Benefit Plan Income | (46.5) | (43.5) | (52.1)
Intercompany Income Allocations | (2.6) | (2.1) | (3.6)
PSNH | Pension and SERP |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service Cost | 4.3 | 4.3 | 6.9
Interest Cost | 26.8 | 27.3 | 16.9
Expected Return on Plan Assets | (48.9) | (49.5) | (56.1)
Actuarial Loss/(Gain) | 5.0 | 1.5 | 7.9
Prior Service Cost/(Credit) | 0.0 | 0.0 | 0.0
Settlement Loss | 0.0 | 0.0 |
Total Net Periodic Benefit Plan Income | (12.8) | (16.4) | (24.4)
Intercompany Income Allocations | (0.4) | (0.8) | (3.6)
PSNH | PBOP |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Service Cost | 0.6 | 0.7 | 1.1
Interest Cost | 3.4 | 3.7 | 2.2
Expected Return on Plan Assets | (5.6) | (5.5) | (6.7)
Actuarial Loss/(Gain) | 0.0 | 0.0 | 0.0
Prior Service Cost/(Credit) | 0.4 | 0.4 | 0.4
Settlement Loss | 0.0 | 0.0 |
Total Net Periodic Benefit Plan Income | (1.2) | (0.7) | (3.0)
Intercompany Income Allocations | $ (0.9) | $ (0.7) | $ (1.2)

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