COMMITMENTS AND CONTINGENCIES - Schedule of Estimated Future Annual Costs of Long term Contractual Agreement (Details) $ in Millions	Dec. 31, 2023 USD ($)
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	$ 1,315.8
2025	1,376.8
2026	1,228.8
2027	1,205.3
2028	1,169.7
Thereafter	6,659.9
Total	12,956.3
Renewable Energy Purchase Contracts
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	769.4
2025	863.0
2026	867.9
2027	897.6
2028	893.1
Thereafter	5,368.8
Total	9,659.8
Natural Gas Procurement
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	423.2
2025	402.3
2026	317.8
2027	264.8
2028	236.0
Thereafter	1,211.8
Total	2,855.9
Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	86.7
2025	75.2
2026	2.9
2027	2.7
2028	2.7
Thereafter	4.5
Total	174.7
Peaker CfDs
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	17.2
2025	14.1
2026	12.8
2027	9.1
2028	6.8
Thereafter	43.7
Total	103.7
Transmission Support Commitments
Transmission Support Commitments
2024	19.3
2025	22.2
2026	27.4
2027	31.1
2028	31.1
Thereafter	31.1
Total	162.2
CL&P
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	727.4
2025	723.6
2026	651.7
2027	652.6
2028	651.3
Thereafter	2,143.8
Total	5,550.4
CL&P | Renewable Energy Purchase Contracts
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	618.8
2025	628.3
2026	628.0
2027	631.2
2028	632.2
Thereafter	2,087.8
Total	5,226.3
CL&P | Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	83.8
2025	72.4
2026	0.1
2027	0.0
2028	0.0
Thereafter	0.0
Total	156.3
CL&P | Peaker CfDs
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	17.2
2025	14.1
2026	12.8
2027	9.1
2028	6.8
Thereafter	43.7
Total	103.7
CL&P | Transmission Support Commitments
Transmission Support Commitments
2024	7.6
2025	8.8
2026	10.8
2027	12.3
2028	12.3
Thereafter	12.3
Total	64.1
NSTAR Electric
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	133.5
2025	214.4
2026	220.1
2027	224.3
2028	220.1
Thereafter	3,000.3
Total	4,012.7
NSTAR Electric | Renewable Energy Purchase Contracts
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	123.0
2025	202.9
2026	206.5
2027	209.3
2028	205.1
Thereafter	2,983.5
Total	3,930.3
NSTAR Electric | Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	2.9
2025	2.8
2026	2.8
2027	2.7
2028	2.7
Thereafter	4.5
Total	18.4
NSTAR Electric | Transmission Support Commitments
Transmission Support Commitments
2024	7.6
2025	8.7
2026	10.8
2027	12.3
2028	12.3
Thereafter	12.3
Total	64.0
PSNH
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	31.7
2025	36.5
2026	39.2
2027	63.6
2028	62.3
Thereafter	304.0
Total	537.3
PSNH | Renewable Energy Purchase Contracts
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	27.6
2025	31.8
2026	33.4
2027	57.1
2028	55.8
Thereafter	297.5
Total	503.2
PSNH | Transmission Support Commitments
Transmission Support Commitments
2024	4.1
2025	4.7
2026	5.8
2027	6.5
2028	6.5
Thereafter	6.5
Total	$ 34.1