REGULATORY ACCOUNTING - Narrative (Details) - USD ($) $ in Millions |
Jun. 30, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Regulatory Assets [Line Items] | ||
| Amount of regulatory costs not yet approved | $ 259.2 | $ 221.0 |
| Regulatory costs | 124.8 | 92.5 |
| CL&P | ||
| Regulatory Assets [Line Items] | ||
| Amount of regulatory costs not yet approved | 138.9 | 116.3 |
| Regulatory costs | 68.2 | 47.2 |
| NSTAR Electric | ||
| Regulatory Assets [Line Items] | ||
| Amount of regulatory costs not yet approved | 47.5 | 41.1 |
| Regulatory costs | 31.8 | 24.4 |
| PSNH | ||
| Regulatory Assets [Line Items] | ||
| Amount of regulatory costs not yet approved | $ 7.0 | $ 4.5 |