v3.26.1
REGULATORY ACCOUNTING - Narrative (Details) - USD ($)
$ in Millions
 6 Months Ended
Jun. 30, 2026
Jul. 29, 2026
Dec. 31, 2025
Regulatory Assets [Line Items]      
Regulatory assets $ 7,146.2   $ 7,693.7
Amount of regulatory costs not yet approved 276.1   244.2
Regulatory costs 151.6   123.2
Regulatory liabilities 5,927.5   5,538.1
Water Distribution | Aquarion      
Regulatory Assets [Line Items]      
Regulatory assets     234.7
Regulatory liabilities     150.8
FERC ROE First Complaint      
Regulatory Assets [Line Items]      
Regulatory liabilities 62.0    
CL&P      
Regulatory Assets [Line Items]      
Regulatory assets 1,991.0   1,981.4
Amount of regulatory costs not yet approved 139.6   127.1
Regulatory costs 70.6   57.0
Regulatory liabilities 2,133.4   1,862.6
CL&P | Catastrophic Storm Costs      
Regulatory Assets [Line Items]      
Storm costs 974.2    
Amount of regulatory costs not yet approved 397.0    
CL&P | Catastrophic Storm Costs | Subsequent Event      
Regulatory Assets [Line Items]      
Amount of regulatory costs not yet approved   $ 63.3  
Approved cost recovery amount   869.4  
Approved cost recovery amount for securitization   667.9  
Recovery amount collected through base rates   101.5  
Approved cost recovery amount RAM proceeding   $ 100.0  
CL&P | FERC ROE Complaints      
Regulatory Assets [Line Items]      
Regulatory liabilities 29.8    
NSTAR Electric      
Regulatory Assets [Line Items]      
Regulatory assets 2,599.4   2,802.3
Amount of regulatory costs not yet approved 56.9   51.0
Regulatory costs 39.8   34.0
Regulatory liabilities 2,503.6   2,352.9
NSTAR Electric | FERC ROE Complaints      
Regulatory Assets [Line Items]      
Regulatory liabilities 24.6    
PSNH      
Regulatory Assets [Line Items]      
Regulatory assets 963.6   961.1
Amount of regulatory costs not yet approved 5.1   5.4
Regulatory liabilities 583.1   $ 535.8
PSNH | FERC ROE Complaints      
Regulatory Assets [Line Items]      
Regulatory liabilities $ 7.6