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EMPLOYEE BENEFITS - Schedule of Pension Benefit Obligations (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Pension Plan |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | $ (7,045.3) | $ (6,321.7) |
Service Cost | (85.8) | (76.2) | $ (67.7)
Interest Cost | (130.0) | (177.8) | (219.0)
Actuarial Gain/(Loss) | 177.1 | (658.2) |
Benefits Paid | 309.5 | 279.3 |
Benefits Paid - Lump Sum | 34.7 | 23.4 |
Benefits Paid - SERP | 10.1 | 7.3 |
Employee Transfers | 0.0 | 0.0 |
Increase due to acquisition of CMA | 0.0 | (121.4) |
Benefit Obligation as of End of Year | (6,729.7) | (7,045.3) | (6,321.7)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 5,409.2 | 4,968.6 |
Employer Contributions | 180.0 | 109.6 |
Actual Return on Plan Assets | 1,250.5 | 512.3 |
Benefits Paid - Pension | (309.5) | (279.3) |
Benefits Paid - Lump Sum | (34.7) | (23.4) |
Employee Transfers | 0.0 | 0.0 |
Increase due to acquisition of CMA | 0.0 | 121.4 |
Fair Value of Plan Assets as of End of Year | 6,495.5 | 5,409.2 | 4,968.6
Funded Status as of December 31st | (234.2) | (1,636.1) |
Other Postretirement Benefits Plan |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | (993.9) | (899.0) |
Service Cost | (13.5) | (10.2) | (7.8)
Interest Cost | (17.4) | (24.6) | (32.7)
Actuarial Gain/(Loss) | 81.4 | (82.8) |
Benefits Paid | 51.7 | 50.2 |
Employee Transfers | 0.0 | 0.0 |
Increase due to acquisition of CMA | 7.4 | (27.5) |
Benefit Obligation as of End of Year | (884.3) | (993.9) | (899.0)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 1,004.1 | 935.9 |
Employer Contributions | 2.3 | 1.9 |
Actual Return on Plan Assets | 183.2 | 116.5 |
Benefits Paid - Pension | (51.3) | (50.2) |
Employee Transfers | 0.0 | 0.0 |
Fair Value of Plan Assets as of End of Year | 1,138.3 | 1,004.1 | 935.9
Funded Status as of December 31st | 254.0 | 10.2 |
The Connecticut Light and Power Company | Pension Plan |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | (1,477.3) | (1,331.3) |
Service Cost | (23.0) | (21.8) | (18.0)
Interest Cost | (27.3) | (37.3) | (45.7)
Actuarial Gain/(Loss) | 127.8 | (152.3) |
Benefits Paid | 64.6 | 63.6 |
Benefits Paid - Lump Sum | 0.0 | 0.0 |
Benefits Paid - SERP | 0.3 | 0.3 |
Employee Transfers | 4.0 | 1.5 |
Increase due to acquisition of CMA | 0.0 | 0.0 |
Benefit Obligation as of End of Year | (1,330.9) | (1,477.3) | (1,331.3)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 1,043.1 | 986.2 |
Employer Contributions | 98.9 | 23.2 |
Actual Return on Plan Assets | 250.4 | 98.8 |
Benefits Paid - Pension | (64.6) | (63.6) |
Benefits Paid - Lump Sum | 0.0 | 0.0 |
Employee Transfers | (4.0) | (1.5) |
Increase due to acquisition of CMA | 0.0 | 0.0 |
Fair Value of Plan Assets as of End of Year | 1,323.8 | 1,043.1 | 986.2
Funded Status as of December 31st | (7.1) | (434.2) |
The Connecticut Light and Power Company | Other Postretirement Benefits Plan |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | (178.6) | (172.7) |
Service Cost | (2.3) | (1.7) | (1.4)
Interest Cost | (3.2) | (4.4) | (6.3)
Actuarial Gain/(Loss) | 5.8 | (8.6) |
Benefits Paid | 10.9 | 10.1 |
Employee Transfers | 1.9 | (1.3) |
Increase due to acquisition of CMA | 0.0 | 0.0 |
Benefit Obligation as of End of Year | (165.5) | (178.6) | (172.7)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 134.1 | 126.3 |
Employer Contributions | 0.0 | 0.0 |
Actual Return on Plan Assets | 24.1 | 15.7 |
Benefits Paid - Pension | (10.9) | (10.1) |
Employee Transfers | (1.6) | 2.2 |
Fair Value of Plan Assets as of End of Year | 145.7 | 134.1 | 126.3
Funded Status as of December 31st | (19.8) | (44.5) |
NSTAR Electric Company | Pension Plan |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | (1,517.9) | (1,397.3) |
Service Cost | (15.8) | (15.4) | (14.6)
Interest Cost | (26.8) | (38.6) | (49.0)
Actuarial Gain/(Loss) | 20.8 | (139.5) |
Benefits Paid | 68.7 | 59.4 |
Benefits Paid - Lump Sum | 15.6 | 13.1 |
Benefits Paid - SERP | 0.2 | 0.2 |
Employee Transfers | 6.8 | 0.2 |
Increase due to acquisition of CMA | 0.0 | 0.0 |
Benefit Obligation as of End of Year | (1,448.4) | (1,517.9) | (1,397.3)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 1,345.1 | 1,288.8 |
Employer Contributions | 30.0 | 0.7 |
Actual Return on Plan Assets | 312.0 | 128.3 |
Benefits Paid - Pension | (68.7) | (59.4) |
Benefits Paid - Lump Sum | (15.6) | (13.1) |
Employee Transfers | (6.8) | (0.2) |
Increase due to acquisition of CMA | 0.0 | 0.0 |
Fair Value of Plan Assets as of End of Year | 1,596.0 | 1,345.1 | 1,288.8
Funded Status as of December 31st | 147.6 | (172.8) |
NSTAR Electric Company | Other Postretirement Benefits Plan |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | (260.5) | (258.3) |
Service Cost | (2.4) | (2.1) | (1.7)
Interest Cost | (4.4) | (6.6) | (9.5)
Actuarial Gain/(Loss) | 11.5 | (7.4) |
Benefits Paid | 16.3 | 14.9 |
Employee Transfers | 1.1 | (1.0) |
Increase due to acquisition of CMA | 0.0 | 0.0 |
Benefit Obligation as of End of Year | (238.4) | (260.5) | (258.3)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 464.6 | 424.4 |
Employer Contributions | 0.0 | 0.0 |
Actual Return on Plan Assets | 84.2 | 53.3 |
Benefits Paid - Pension | (16.3) | (14.9) |
Employee Transfers | (2.5) | 1.8 |
Fair Value of Plan Assets as of End of Year | 530.0 | 464.6 | 424.4
Funded Status as of December 31st | 291.6 | 204.1 |
Public Service Company of New Hampshire | Pension Plan |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | (748.7) | (692.6) |
Service Cost | (8.9) | (8.2) | (7.1)
Interest Cost | (14.5) | (19.4) | (24.0)
Actuarial Gain/(Loss) | 14.7 | (62.1) |
Benefits Paid | 34.7 | 33.5 |
Benefits Paid - Lump Sum | 0.0 | 0.0 |
Benefits Paid - SERP | 0.4 | 0.4 |
Employee Transfers | 1.3 | (0.3) |
Increase due to acquisition of CMA | 0.0 | 0.0 |
Benefit Obligation as of End of Year | (721.0) | (748.7) | (692.6)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 593.7 | 551.6 |
Employer Contributions | 0.0 | 19.5 |
Actual Return on Plan Assets | 136.9 | 55.8 |
Benefits Paid - Pension | (34.7) | (33.5) |
Benefits Paid - Lump Sum | 0.0 | 0.0 |
Employee Transfers | (1.3) | 0.3 |
Increase due to acquisition of CMA | 0.0 | 0.0 |
Fair Value of Plan Assets as of End of Year | 694.6 | 593.7 | 551.6
Funded Status as of December 31st | (26.4) | (155.0) |
Public Service Company of New Hampshire | Other Postretirement Benefits Plan |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Benefit Obligation as of Beginning of Year | (109.5) | (93.0) |
Service Cost | (1.2) | (0.9) | (0.7)
Interest Cost | (1.8) | (2.8) | (3.4)
Actuarial Gain/(Loss) | 14.6 | (19.0) |
Benefits Paid | 5.6 | 6.1 |
Employee Transfers | 0.0 | 0.1 |
Increase due to acquisition of CMA | 0.0 | 0.0 |
Benefit Obligation as of End of Year | (92.3) | (109.5) | (93.0)
Change in Pension Plan Assets: |  |  |
Fair Value of Plan Assets as of Beginning of Year | 79.4 | 76.0 |
Employer Contributions | 0.0 | 0.0 |
Actual Return on Plan Assets | 14.2 | 9.3 |
Benefits Paid - Pension | (5.6) | (6.1) |
Employee Transfers | 0.0 | 0.2 |
Fair Value of Plan Assets as of End of Year | 88.0 | 79.4 | $ 76.0
Funded Status as of December 31st | $ (4.3) | $ (30.1) |

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