COMMITMENTS AND CONTINGENCIES - Schedule of Estimated Future Annual Costs of Long term Contractual Agreement (Details) $ in Millions	Dec. 31, 2025 USD ($)
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2026	$ 1,785.0
2027	1,869.7
2028	1,755.1
2029	1,588.6
2030	1,204.9
Thereafter	14,311.4
Total	22,514.7
Renewable Energy Purchase Contracts
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2026	1,113.9
2027	1,235.1
2028	1,246.2
2029	1,115.5
2030	784.1
Thereafter	11,643.4
Total	17,138.2
Natural Gas Procurement
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2026	523.3
2027	487.9
2028	359.4
2029	320.1
2030	273.6
Thereafter	781.9
Total	2,746.2
NECEC Transmission Service Agreement
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2026	94.6
2027	96.5
2028	98.4
2029	100.4
2030	102.4
Thereafter	1,806.4
Total	2,298.7
Capacity and Purchased Power
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2026	2.9
2027	2.7
2028	2.7
2029	2.3
2030	1.8
Thereafter	0.5
Total	12.9
Peaker CfDs
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2026	30.2
2027	25.9
2028	25.8
2029	26.2
2030	18.9
Thereafter	55.1
Total	182.1
Transmission Support Commitments
Transmission Support Commitments
2026	20.1
2027	21.6
2028	22.6
2029	24.1
2030	24.1
Thereafter	24.1
Total	136.6
CL&P
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2026	720.0
2027	809.0
2028	815.1
2029	675.7
2030	328.8
Thereafter	3,667.8
Total	7,016.4
CL&P | Renewable Energy Purchase Contracts
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2026	681.8
2027	774.6
2028	780.4
2029	640.0
2030	300.4
Thereafter	3,603.2
Total	6,780.4
CL&P | Capacity and Purchased Power
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2026	0.1
2027	0.0
2028	0.0
2029	0.0
2030	0.0
Thereafter	0.0
Total	0.1
CL&P | Peaker CfDs
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2026	30.2
2027	25.9
2028	25.8
2029	26.2
2030	18.9
Thereafter	55.1
Total	182.1
CL&P | Transmission Support Commitments
Transmission Support Commitments
2026	7.9
2027	8.5
2028	8.9
2029	9.5
2030	9.5
Thereafter	9.5
Total	53.8
NSTAR Electric
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2026	537.4
2027	568.2
2028	575.8
2029	587.7
2030	597.4
Thereafter	9,856.6
Total	12,723.1
NSTAR Electric | Renewable Energy Purchase Contracts
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2026	432.1
2027	460.5
2028	465.8
2029	475.5
2030	483.7
Thereafter	8,040.2
Total	10,357.8
NSTAR Electric | NECEC Transmission Service Agreement
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2026	94.6
2027	96.5
2028	98.4
2029	100.4
2030	102.4
Thereafter	1,806.4
Total	2,298.7
NSTAR Electric | Capacity and Purchased Power
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2026	2.8
2027	2.7
2028	2.7
2029	2.3
2030	1.8
Thereafter	0.5
Total	12.8
NSTAR Electric | Transmission Support Commitments
Transmission Support Commitments
2026	7.9
2027	8.5
2028	8.9
2029	9.5
2030	9.5
Thereafter	9.5
Total	53.8
PSNH | Transmission Support Commitments
Transmission Support Commitments
2026	4.3
2027	4.6
2028	4.8
2029	5.1
2030	5.1
Thereafter	5.1
Total	$ 29.0