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EMPLOYEE BENEFITS - Schedule of Pension Benefit Obligations (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Pension and SERP |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | $ (5,220.1) | $ (6,729.7) |
Service Cost | (43.1) | (70.1) | $ (85.8)
Interest Cost | (254.0) | (154.5) | (130.0)
Actuarial Gain/(Loss) | (110.4) | 1,385.8 |
Benefits Paid | 317.3 | 302.5 |
Benefits Paid - Lump Sum | 28.9 | 33.0 |
Benefits Paid - SERP | 43.0 | 12.9 |
Employee Transfers | 0.0 | 0.0 |
Benefit Obligation as of End of Year | (5,238.4) | (5,220.1) | (6,729.7)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 5,806.4 | 6,495.5 |
Employer Contributions | 5.0 | 80.0 |
Actual Return on Plan Assets | 309.8 | (433.6) |
Benefits Paid - Pension | (317.3) | (302.5) |
Benefits Paid - Lump Sum | (28.9) | (33.0) |
Employee Transfers | 0.0 | 0.0 |
Fair Value of Plan Assets as of End of Year | 5,775.0 | 5,806.4 | 6,495.5
Funded Status as of December 31st | 536.6 | 586.3 |
PBOP |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | (693.7) | (884.3) |
Service Cost | (7.6) | (11.6) | (13.5)
Interest Cost | (33.8) | (20.2) | (17.4)
Actuarial Gain/(Loss) | 5.0 | 173.6 |
Benefits Paid | 52.7 | 52.1 |
Employee Transfers | 0.0 | 0.0 |
Plan Amendment | 1.4 | 0.0 |
Impact of Acquisitions | 0.0 | (3.3) |
Benefit Obligation as of End of Year | (676.0) | (693.7) | (884.3)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 970.1 | 1,138.3 |
Employer Contributions | 1.9 | 3.1 |
Actual Return on Plan Assets | 104.7 | (119.6) |
Benefits Paid - Pension | (52.3) | (51.7) |
Employee Transfers | 0.0 | 0.0 |
Fair Value of Plan Assets as of End of Year | 1,024.4 | 970.1 | 1,138.3
Funded Status as of December 31st | 348.4 | 276.4 |
CL&P | Pension and SERP |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | (1,030.0) | (1,330.9) |
Service Cost | (12.3) | (18.7) | (23.0)
Interest Cost | (50.5) | (31.3) | (27.3)
Actuarial Gain/(Loss) | (19.7) | 284.1 |
Benefits Paid | 66.1 | 63.3 |
Benefits Paid - Lump Sum | 0.0 | 0.0 |
Benefits Paid - SERP | 0.3 | 0.3 |
Employee Transfers | (2.4) | 3.2 |
Benefit Obligation as of End of Year | (1,048.5) | (1,030.0) | (1,330.9)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 1,172.0 | 1,323.8 |
Employer Contributions | 0.0 | 0.0 |
Actual Return on Plan Assets | 61.7 | (85.3) |
Benefits Paid - Pension | (66.1) | (63.3) |
Benefits Paid - Lump Sum | 0.0 | 0.0 |
Employee Transfers | 2.4 | (3.2) |
Fair Value of Plan Assets as of End of Year | 1,170.0 | 1,172.0 | 1,323.8
Funded Status as of December 31st | 121.5 | 142.0 |
CL&P | PBOP |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | (127.9) | (165.5) |
Service Cost | (1.3) | (2.0) | (2.3)
Interest Cost | (6.2) | (3.7) | (3.2)
Actuarial Gain/(Loss) | 4.4 | 33.0 |
Benefits Paid | 10.0 | 10.4 |
Employee Transfers | 0.0 | (0.1) |
Plan Amendment | 0.4 | 0.0 |
Impact of Acquisitions | 0.0 | 0.0 |
Benefit Obligation as of End of Year | (120.6) | (127.9) | (165.5)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 120.6 | 145.7 |
Employer Contributions | 0.0 | 0.0 |
Actual Return on Plan Assets | 12.6 | (15.0) |
Benefits Paid - Pension | (10.0) | (10.4) |
Employee Transfers | (0.2) | 0.3 |
Fair Value of Plan Assets as of End of Year | 123.0 | 120.6 | 145.7
Funded Status as of December 31st | 2.4 | (7.3) |
NSTAR Electric | Pension and SERP |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | (1,110.4) | (1,448.4) |
Service Cost | (7.8) | (13.8) | (15.8)
Interest Cost | (53.9) | (32.8) | (26.8)
Actuarial Gain/(Loss) | (17.6) | 295.5 |
Benefits Paid | 76.7 | 68.4 |
Benefits Paid - Lump Sum | 5.3 | 14.8 |
Benefits Paid - SERP | 0.2 | 0.2 |
Employee Transfers | 0.5 | 5.7 |
Benefit Obligation as of End of Year | (1,107.0) | (1,110.4) | (1,448.4)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 1,418.8 | 1,596.0 |
Employer Contributions | 0.0 | 15.0 |
Actual Return on Plan Assets | 75.3 | (103.3) |
Benefits Paid - Pension | (76.7) | (68.4) |
Benefits Paid - Lump Sum | (5.3) | (14.8) |
Employee Transfers | (0.5) | (5.7) |
Fair Value of Plan Assets as of End of Year | 1,411.6 | 1,418.8 | 1,596.0
Funded Status as of December 31st | 304.6 | 308.4 |
NSTAR Electric | PBOP |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | (189.5) | (238.4) |
Service Cost | (1.2) | (2.0) | (2.4)
Interest Cost | (9.2) | (5.3) | (4.4)
Actuarial Gain/(Loss) | (5.8) | 39.4 |
Benefits Paid | 16.7 | 16.6 |
Employee Transfers | 0.5 | 0.2 |
Plan Amendment | 0.2 | 0.0 |
Impact of Acquisitions | 0.0 | 0.0 |
Benefit Obligation as of End of Year | (188.3) | (189.5) | (238.4)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 456.1 | 530.0 |
Employer Contributions | 0.0 | 0.0 |
Actual Return on Plan Assets | 52.3 | (57.0) |
Benefits Paid - Pension | (16.7) | (16.6) |
Employee Transfers | (1.3) | (0.3) |
Fair Value of Plan Assets as of End of Year | 490.4 | 456.1 | 530.0
Funded Status as of December 31st | 302.1 | 266.6 |
PSNH | Pension and SERP |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | (556.2) | (721.0) |
Service Cost | (4.3) | (6.9) | (8.9)
Interest Cost | (27.3) | (16.9) | (14.5)
Actuarial Gain/(Loss) | (11.6) | 156.7 |
Benefits Paid | 35.7 | 33.9 |
Benefits Paid - Lump Sum | 1.0 | 1.0 |
Benefits Paid - SERP | 0.4 | 0.4 |
Employee Transfers | 0.0 | (3.4) |
Benefit Obligation as of End of Year | (562.3) | (556.2) | (721.0)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 618.0 | 694.6 |
Employer Contributions | 0.0 | 0.0 |
Actual Return on Plan Assets | 32.7 | (45.1) |
Benefits Paid - Pension | (35.7) | (33.9) |
Benefits Paid - Lump Sum | (1.0) | (1.0) |
Employee Transfers | 0.0 | 3.4 |
Fair Value of Plan Assets as of End of Year | 614.0 | 618.0 | 694.6
Funded Status as of December 31st | 51.7 | 61.8 |
PSNH | PBOP |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | (74.6) | (92.3) |
Service Cost | (0.7) | (1.1) | (1.2)
Interest Cost | (3.7) | (2.2) | (1.8)
Actuarial Gain/(Loss) | 0.8 | 15.2 |
Benefits Paid | 6.1 | 6.0 |
Employee Transfers | (0.1) | (0.2) |
Plan Amendment | 0.2 | 0.0 |
Impact of Acquisitions | 0.0 | 0.0 |
Benefit Obligation as of End of Year | (72.0) | (74.6) | (92.3)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 72.3 | 88.0 |
Employer Contributions | 0.0 | 0.0 |
Actual Return on Plan Assets | 8.3 | (9.8) |
Benefits Paid - Pension | (6.1) | (6.0) |
Employee Transfers | 0.2 | 0.1 |
Fair Value of Plan Assets as of End of Year | 74.7 | 72.3 | $ 88.0
Funded Status as of December 31st | $ 2.7 | $ (2.3) |

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