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PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSION - Components of Net Periodic Benefit Expense/(Income) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2022 | Jun. 30, 2021 | Jun. 30, 2022 | Jun. 30, 2021
Pension and SERP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | $ 17.5 | $ 18.4 | $ 35.2 | $ 39.7
Interest Cost | 38.6 | 27.1 | 77.2 | 59.7
Expected Return on Plan Assets | (130.7) | (87.4) | (262.4) | (196.3)
Actuarial Losses, net | 28.4 | 47.8 | 59.1 | 109.4
Prior Service Cost/(Credit) | 0.3 | 0.3 | 0.7 | 0.6
Total Net Periodic Benefit Plan Income | (45.9) | 6.2 | (90.2) | 13.1
PBOP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | 3.0 | 3.3 | 5.8 | 6.8
Interest Cost | 5.1 | 4.2 | 10.1 | 8.6
Expected Return on Plan Assets | (22.6) | (19.8) | (45.0) | (39.5)
Actuarial Losses, net | 0.0 | 1.3 | 0.0 | 3.9
Prior Service Cost/(Credit) | (5.4) | (5.3) | (10.8) | (10.6)
Total Net Periodic Benefit Plan Income | (19.9) | (16.3) | (39.9) | (30.8)
CL&P | Pension and SERP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | 4.7 | 5.5 | 9.2 | 11.8
Interest Cost | 7.8 | 6.7 | 15.6 | 14.0
Expected Return on Plan Assets | (26.5) | (21.7) | (53.1) | (43.3)
Actuarial Losses, net | 4.0 | 10.8 | 8.2 | 23.8
Prior Service Cost/(Credit) | 0.0 | 0.0 | 0.0 | 0.0
Total Net Periodic Benefit Plan Income | (10.0) | 1.3 | (20.1) | 6.3
Intercompany Income Allocations | (4.1) | 2.3 | (7.9) | 3.6
CL&P | PBOP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | 0.5 | 0.6 | 1.0 | 1.2
Interest Cost | 0.9 | 0.8 | 1.8 | 1.6
Expected Return on Plan Assets | (2.8) | (2.6) | (5.6) | (5.2)
Actuarial Losses, net | 0.0 | 0.4 | 0.0 | 0.8
Prior Service Cost/(Credit) | 0.3 | 0.3 | 0.5 | 0.5
Total Net Periodic Benefit Plan Income | (1.1) | (0.5) | (2.3) | (1.1)
Intercompany Income Allocations | (0.9) | (0.6) | (1.8) | (0.9)
NSTAR Electric | Pension and SERP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | 3.4 | 3.9 | 7.0 | 7.9
Interest Cost | 8.2 | 6.7 | 16.3 | 13.4
Expected Return on Plan Assets | (32.1) | (27.1) | (64.1) | (54.0)
Actuarial Losses, net | 8.1 | 15.3 | 16.6 | 30.8
Prior Service Cost/(Credit) | 0.1 | 0.1 | 0.2 | 0.2
Total Net Periodic Benefit Plan Income | (12.3) | (1.1) | (24.0) | (1.7)
Intercompany Income Allocations | (3.2) | 2.5 | (6.1) | 4.0
NSTAR Electric | PBOP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | 0.5 | 0.6 | 1.0 | 1.2
Interest Cost | 1.3 | 1.1 | 2.6 | 2.2
Expected Return on Plan Assets | (10.6) | (9.2) | (21.2) | (18.5)
Actuarial Losses, net | 0.0 | 0.5 | 0.0 | 1.1
Prior Service Cost/(Credit) | (4.2) | (4.2) | (8.5) | (8.4)
Total Net Periodic Benefit Plan Income | (13.0) | (11.2) | (26.1) | (22.4)
Intercompany Income Allocations | (0.9) | (0.6) | (1.8) | (1.0)
PSNH | Pension and SERP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | 1.7 | 2.2 | 3.5 | 4.4
Interest Cost | 4.2 | 3.6 | 8.4 | 7.2
Expected Return on Plan Assets | (14.0) | (11.8) | (28.1) | (23.7)
Actuarial Losses, net | 1.9 | 5.2 | 4.1 | 10.1
Prior Service Cost/(Credit) | 0.0 | 0.0 | 0.0 | 0.0
Total Net Periodic Benefit Plan Income | (6.2) | (0.8) | (12.1) | (2.0)
Intercompany Income Allocations | (0.9) | 0.7 | (1.7) | 1.2
PSNH | PBOP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | 0.3 | 0.3 | 0.5 | 0.6
Interest Cost | 0.6 | 0.4 | 1.1 | 0.9
Expected Return on Plan Assets | (1.7) | (1.5) | (3.3) | (3.0)
Actuarial Losses, net | 0.0 | 0.1 | 0.0 | 0.3
Prior Service Cost/(Credit) | 0.1 | 0.1 | 0.2 | 0.2
Total Net Periodic Benefit Plan Income | (0.7) | (0.6) | (1.5) | (1.0)
Intercompany Income Allocations | $ (0.3) | $ (0.2) | $ (0.6) | $ (0.3)

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