LONG-TERM DEBT - Schedule of Long-term Debt Maturities (Details) $ in Millions	Dec. 31, 2025 USD ($)
Debt Instrument [Line Items]
2026	$ 1,390.5
2027	2,889.5
2028	2,278.8
2029	2,300.5
2030	2,904.0
Thereafter	16,594.2
Total	28,357.5
CL&P
Debt Instrument [Line Items]
2026	0.0
2027	500.0
2028	0.0
2029	350.0
2030	400.0
Thereafter	3,880.0
Total	5,130.0
NSTAR Electric
Debt Instrument [Line Items]
2026	300.0
2027	700.0
2028	150.0
2029	400.0
2030	800.0
Thereafter	3,640.0
Total	5,990.0
PSNH
Debt Instrument [Line Items]
2026	0.0
2027	0.0
2028	300.0
2029	0.0
2030	0.0
Thereafter	1,750.0
Total	$ 2,050.0