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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
--- | ---
Mar. 31, 2023 | Mar. 31, 2022
Pension and SERP |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Service Cost | $ 11.0 | $ 17.7
Interest Cost | 63.7 | 38.6
Expected Return on Plan Assets | (115.9) | (131.7)
Actuarial Losses, net | 12.5 | 30.7
Prior Service Cost/(Credit) | 0.3 | 0.4
Total Net Periodic Benefit Plan Income | (28.4) | (44.3)
PBOP |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Service Cost | 1.8 | 2.8
Interest Cost | 8.5 | 5.0
Expected Return on Plan Assets | (19.1) | (22.4)
Actuarial Losses, net | 0.0 | 0.0
Prior Service Cost/(Credit) | (5.4) | (5.4)
Total Net Periodic Benefit Plan Income | (14.2) | (20.0)
CL&P | Pension and SERP |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Service Cost | 3.0 | 4.5
Interest Cost | 12.6 | 7.8
Expected Return on Plan Assets | (23.4) | (26.6)
Actuarial Losses, net | 0.8 | 4.2
Prior Service Cost/(Credit) | 0.0 | 0.0
Total Net Periodic Benefit Plan Income | (7.0) | (10.1)
Intercompany Income Allocations | (2.0) | (3.8)
CL&P | PBOP |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Service Cost | 0.3 | 0.5
Interest Cost | 1.6 | 0.9
Expected Return on Plan Assets | (2.4) | (2.8)
Actuarial Losses, net | 0.0 | 0.0
Prior Service Cost/(Credit) | 0.3 | 0.2
Total Net Periodic Benefit Plan Income | (0.2) | (1.2)
Intercompany Income Allocations | (0.5) | (0.9)
NSTAR Electric | Pension and SERP |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Service Cost | 2.1 | 3.6
Interest Cost | 13.5 | 8.1
Expected Return on Plan Assets | (28.4) | (32.0)
Actuarial Losses, net | 4.9 | 8.5
Prior Service Cost/(Credit) | 0.1 | 0.1
Total Net Periodic Benefit Plan Income | (7.8) | (11.7)
Intercompany Income Allocations | (1.7) | (2.9)
NSTAR Electric | PBOP |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Service Cost | 0.3 | 0.5
Interest Cost | 2.3 | 1.3
Expected Return on Plan Assets | (9.2) | (10.6)
Actuarial Losses, net | 0.0 | 0.0
Prior Service Cost/(Credit) | (4.2) | (4.3)
Total Net Periodic Benefit Plan Income | (10.8) | (13.1)
Intercompany Income Allocations | (0.6) | (0.9)
PSNH | Pension and SERP |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Service Cost | 1.1 | 1.8
Interest Cost | 6.8 | 4.2
Expected Return on Plan Assets | (12.3) | (14.1)
Actuarial Losses, net | 0.4 | 2.2
Prior Service Cost/(Credit) | 0.0 | 0.0
Total Net Periodic Benefit Plan Income | (4.0) | (5.9)
Intercompany Income Allocations | (0.5) | (0.8)
PSNH | PBOP |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Service Cost | 0.2 | 0.2
Interest Cost | 0.9 | 0.5
Expected Return on Plan Assets | (1.4) | (1.6)
Actuarial Losses, net | 0.0 | 0.0
Prior Service Cost/(Credit) | 0.1 | 0.1
Total Net Periodic Benefit Plan Income | (0.2) | (0.8)
Intercompany Income Allocations | $ (0.2) | $ (0.3)

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