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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 | 9 Months Ended
--- | --- | ---
Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2022 | Sep. 30, 2021
Pension and SERP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | $ 17.5 | $ 21.5 | $ 52.7 | $ 64.3
Interest Cost | 38.6 | 32.5 | 115.8 | 97.5
Expected Return on Plan Assets | (130.7) | (109.5) | (393.1) | (328.0)
Actuarial Losses, net | 28.4 | 60.7 | 87.5 | 183.1
Prior Service Cost/(Credit) | 0.4 | 0.3 | 1.1 | 1.1
Total Net Periodic Benefit Plan Income | (45.8) | 5.5 | (136.0) | 18.0
PBOP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | 2.9 | 3.3 | 8.7 | 10.1
Interest Cost | 5.0 | 4.3 | 15.1 | 12.9
Expected Return on Plan Assets | (22.5) | (19.8) | (67.5) | (59.3)
Actuarial Losses, net | 0.0 | 2.0 | 0.0 | 5.9
Prior Service Cost/(Credit) | (5.4) | (5.3) | (16.2) | (15.9)
Total Net Periodic Benefit Plan Income | (20.0) | (15.5) | (59.9) | (46.3)
CL&P | Pension and SERP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | 4.7 | 5.6 | 13.9 | 17.4
Interest Cost | 7.8 | 6.7 | 23.4 | 20.7
Expected Return on Plan Assets | (26.5) | (21.7) | (79.6) | (65.0)
Actuarial Losses, net | 4.0 | 10.8 | 12.2 | 34.6
Prior Service Cost/(Credit) | 0.0 | 0.0 | 0.0 | 0.0
Total Net Periodic Benefit Plan Income | (10.0) | 1.4 | (30.1) | 7.7
Intercompany Income Allocations | (4.0) | 2.2 | (11.9) | 5.8
CL&P | PBOP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | 0.5 | 0.5 | 1.5 | 1.7
Interest Cost | 0.9 | 0.8 | 2.7 | 2.4
Expected Return on Plan Assets | (2.8) | (2.5) | (8.4) | (7.7)
Actuarial Losses, net | 0.0 | 0.4 | 0.0 | 1.2
Prior Service Cost/(Credit) | 0.3 | 0.3 | 0.8 | 0.8
Total Net Periodic Benefit Plan Income | (1.1) | (0.5) | (3.4) | (1.6)
Intercompany Income Allocations | (0.9) | (0.4) | (2.7) | (1.3)
NSTAR Electric | Pension and SERP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | 3.4 | 4.0 | 10.4 | 11.9
Interest Cost | 8.2 | 6.7 | 24.5 | 20.1
Expected Return on Plan Assets | (32.1) | (27.1) | (96.2) | (81.1)
Actuarial Losses, net | 8.1 | 15.3 | 24.7 | 46.1
Prior Service Cost/(Credit) | 0.1 | 0.1 | 0.3 | 0.3
Total Net Periodic Benefit Plan Income | (12.3) | (1.0) | (36.3) | (2.7)
Intercompany Income Allocations | (3.2) | 2.4 | (9.3) | 6.4
NSTAR Electric | PBOP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | 0.5 | 0.6 | 1.5 | 1.8
Interest Cost | 1.3 | 1.1 | 3.9 | 3.3
Expected Return on Plan Assets | (10.6) | (9.2) | (31.8) | (27.7)
Actuarial Losses, net | 0.0 | 0.5 | 0.0 | 1.6
Prior Service Cost/(Credit) | (4.2) | (4.3) | (12.7) | (12.7)
Total Net Periodic Benefit Plan Income | (13.0) | (11.3) | (39.1) | (33.7)
Intercompany Income Allocations | (0.9) | (0.5) | (2.7) | (1.5)
PSNH | Pension and SERP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | 1.7 | 2.2 | 5.2 | 6.6
Interest Cost | 4.2 | 3.7 | 12.6 | 10.9
Expected Return on Plan Assets | (14.0) | (11.9) | (42.1) | (35.6)
Actuarial Losses, net | 1.9 | 5.3 | 6.0 | 15.4
Prior Service Cost/(Credit) | 0.0 | 0.0 | 0.0 | 0.0
Total Net Periodic Benefit Plan Income | (6.2) | (0.7) | (18.3) | (2.7)
Intercompany Income Allocations | (1.0) | 0.7 | (2.7) | 1.9
PSNH | PBOP |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |
Service Cost | 0.3 | 0.3 | 0.8 | 0.9
Interest Cost | 0.5 | 0.4 | 1.6 | 1.3
Expected Return on Plan Assets | (1.7) | (1.6) | (5.0) | (4.6)
Actuarial Losses, net | 0.0 | 0.1 | 0.0 | 0.4
Prior Service Cost/(Credit) | 0.1 | 0.1 | 0.3 | 0.3
Total Net Periodic Benefit Plan Income | (0.8) | (0.7) | (2.3) | (1.7)
Intercompany Income Allocations | $ (0.3) | $ (0.2) | $ (0.9) | $ (0.5)

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