v3.26.1
PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSION (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Pension and SERP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost $ 19.3 $ 17.2 $ 37.7 $ 33.6
Interest Cost 60.1 64.1 119.2 127.3
Expected Return on Plan Assets (117.3) (113.7) (234.6) (227.0)
Actuarial Loss/(Gain) 10.6 11.0 19.3 21.0
Prior Service Cost/(Credit) 0.2 0.3 0.4 0.6
Settlement Loss       3.3
Total Net Periodic Benefit Plan Income (27.1) (21.1) (58.0) (41.2)
PBOP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost 1.6 1.6 3.2 3.2
Interest Cost 7.2 8.0 14.4 16.0
Expected Return on Plan Assets (22.9) (21.1) (45.6) (42.3)
Actuarial Loss/(Gain) (0.3) (0.2) (0.7) (0.5)
Prior Service Cost/(Credit) (5.4) (5.4) (10.8) (10.8)
Settlement Loss       0.0
Total Net Periodic Benefit Plan Income (19.8) (17.1) (39.5) (34.4)
CL&P | Pension and SERP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost 4.2 3.8 8.1 7.6
Interest Cost 12.4 12.9 24.5 25.7
Expected Return on Plan Assets (24.0) (23.0) (47.9) (45.9)
Actuarial Loss/(Gain) 1.5 1.3 2.6 2.5
Prior Service Cost/(Credit) 0.0 0.0 0.0 0.0
Settlement Loss       0.0
Total Net Periodic Benefit Plan Income (5.9) (5.0) (12.7) (10.1)
Intercompany Income Allocations (1.3) (0.5) (3.1) (0.4)
CL&P | PBOP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost 0.3 0.3 0.6 0.5
Interest Cost 1.2 1.4 2.5 2.8
Expected Return on Plan Assets (2.4) (2.4) (5.0) (4.8)
Actuarial Loss/(Gain) 0.0 0.0 0.0 0.0
Prior Service Cost/(Credit) 0.2 0.3 0.5 0.6
Settlement Loss       0.0
Total Net Periodic Benefit Plan Income (0.7) (0.4) (1.4) (0.9)
Intercompany Income Allocations (0.7) (0.5) (1.3) (1.0)
NSTAR Electric | Pension and SERP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost 3.6 2.4 6.8 4.9
Interest Cost 12.4 13.4 24.6 26.4
Expected Return on Plan Assets (28.9) (27.7) (57.8) (55.4)
Actuarial Loss/(Gain) 3.4 3.7 6.2 6.9
Prior Service Cost/(Credit) 0.1 0.1 0.2 0.2
Settlement Loss       0.0
Total Net Periodic Benefit Plan Income (9.4) (8.1) (20.0) (17.0)
Intercompany Income Allocations (1.0) (0.3) (2.5) 0.0
NSTAR Electric | PBOP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost 0.2 0.3 0.5 0.5
Interest Cost 1.9 2.2 3.8 4.4
Expected Return on Plan Assets (11.3) (10.5) (22.9) (21.0)
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
Total Net Periodic Benefit Plan Income (13.5) (12.3) (27.1) (24.6)
Intercompany Income Allocations (0.8) (0.7) (1.6) (1.4)
PSNH | Pension and SERP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost 1.7 1.6 3.3 3.2
Interest Cost 6.3 6.8 12.5 13.6
Expected Return on Plan Assets (12.3) (12.0) (24.7) (23.9)
Actuarial Loss/(Gain) 0.4 0.5 0.8 1.0
Prior Service Cost/(Credit) 0.0 0.0 0.0 0.0
Settlement Loss       0.0
Total Net Periodic Benefit Plan Income (3.9) (3.1) (8.1) (6.1)
Intercompany Income Allocations (0.3) (0.1) (0.8) 0.0
PSNH | PBOP        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost 0.1 0.1 0.2 0.2
Interest Cost 0.8 0.8 1.6 1.6
Expected Return on Plan Assets (1.5) (1.4) (3.0) (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
Total Net Periodic Benefit Plan Income (0.5) (0.4) (1.0) (0.8)
Intercompany Income Allocations $ (0.3) $ (0.2) $ (0.6) $ (0.4)