v3.25.2
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, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Pension and SERP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost $ 17.2 $ 11.2 $ 33.6 $ 22.0
Interest Cost 64.1 62.7 127.3 124.7
Expected Return on Plan Assets (113.7) (115.7) (227.0) (231.3)
Actuarial Loss/(Gain) 11.0 22.1 21.0 41.9
Prior Service Cost/(Credit) 0.3 0.3 0.6 0.6
Settlement Loss     3.3 4.3
Total Net Periodic Benefit Plan Income (21.1) (19.4) (41.2) (37.8)
PBOP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost 1.6 1.8 3.2 3.5
Interest Cost 8.0 8.0 16.0 16.0
Expected Return on Plan Assets (21.1) (20.3) (42.3) (40.7)
Actuarial Loss/(Gain) (0.2) (0.1) (0.5) (0.2)
Prior Service Cost/(Credit) (5.4) (5.4) (10.8) (10.8)
Settlement Loss     0.0 0.0
Total Net Periodic Benefit Plan Income (17.1) (16.0) (34.4) (32.2)
CL&P | Pension and SERP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost 3.8 3.3 7.6 6.2
Interest Cost 12.9 12.7 25.7 25.1
Expected Return on Plan Assets (23.0) (23.5) (45.9) (46.8)
Actuarial Loss/(Gain) 1.3 3.2 2.5 5.7
Prior Service Cost/(Credit) 0.0 0.0 0.0 0.0
Settlement Loss     0.0 0.0
Total Net Periodic Benefit Plan Income (5.0) (4.3) (10.1) (9.8)
Intercompany (Income)/Expense Allocations (0.5) (0.6) (0.4) (0.3)
CL&P | 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 1.4 1.4 2.8 2.8
Expected Return on Plan Assets (2.4) (2.3) (4.8) (4.7)
Actuarial Loss/(Gain) 0.0 0.0 0.0 0.0
Prior Service Cost/(Credit) 0.3 0.2 0.6 0.5
Settlement Loss     0.0 0.0
Total Net Periodic Benefit Plan Income (0.4) (0.4) (0.9) (0.8)
Intercompany (Income)/Expense Allocations (0.5) (0.5) (1.0) (1.1)
NSTAR Electric | Pension and SERP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost 2.4 1.9 4.9 4.0
Interest Cost 13.4 12.8 26.4 25.9
Expected Return on Plan Assets (27.7) (28.0) (55.4) (56.3)
Actuarial Loss/(Gain) 3.7 6.4 6.9 12.8
Prior Service Cost/(Credit) 0.1 0.1 0.2 0.2
Settlement Loss     0.0 0.0
Total Net Periodic Benefit Plan Income (8.1) (6.8) (17.0) (13.4)
Intercompany (Income)/Expense Allocations (0.3) (0.6) 0.0 (0.2)
NSTAR Electric | 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 2.2 2.2 4.4 4.4
Expected Return on Plan Assets (10.5) (9.9) (21.0) (19.8)
Actuarial Loss/(Gain) 0.0 0.0 0.0 0.0
Prior Service Cost/(Credit) (4.3) (4.3) (8.5) (8.5)
Settlement Loss     0.0 0.0
Total Net Periodic Benefit Plan Income (12.3) (11.7) (24.6) (23.3)
Intercompany (Income)/Expense Allocations (0.7) (0.6) (1.4) (1.3)
PSNH | Pension and SERP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost 1.6 1.1 3.2 2.1
Interest Cost 6.8 6.7 13.6 13.4
Expected Return on Plan Assets (12.0) (12.2) (23.9) (24.4)
Actuarial Loss/(Gain) 0.5 1.3 1.0 2.4
Prior Service Cost/(Credit) 0.0 0.0 0.0 0.0
Settlement Loss     0.0 0.0
Total Net Periodic Benefit Plan Income (3.1) (3.1) (6.1) (6.5)
Intercompany (Income)/Expense Allocations (0.1) (0.2) 0.0 (0.1)
PSNH | PBOP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost 0.1 0.2 0.2 0.3
Interest Cost 0.8 0.8 1.6 1.7
Expected Return on Plan Assets (1.4) (1.4) (2.8) (2.8)
Actuarial Loss/(Gain) 0.0 0.0 0.0 0.0
Prior Service Cost/(Credit) 0.1 0.1 0.2 0.2
Settlement Loss     0.0 0.0
Total Net Periodic Benefit Plan Income (0.4) (0.3) (0.8) (0.6)
Intercompany (Income)/Expense Allocations $ (0.2) $ (0.2) $ (0.4) $ (0.4)