COMMITMENTS AND CONTINGENCIES - Schedule of Estimated Future Annual Costs of Long term Contractual Agreement (Details) $ in Millions	Dec. 31, 2022 USD ($)
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2023	$ 1,324.6
2024	1,500.6
2025	1,411.4
2026	1,323.0
2027	1,304.6
Thereafter	9,685.9
Total	16,550.1
Renewable Energy Purchase Contracts
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2023	751.8
2024	952.6
2025	954.8
2026	983.0
2027	998.5
Thereafter	8,141.1
Total	12,781.8
Natural Gas Procurement
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2023	447.1
2024	419.4
2025	340.9
2026	298.5
2027	269.4
Thereafter	1,450.6
Total	3,225.9
Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2023	87.6
2024	86.8
2025	75.2
2026	2.9
2027	2.7
Thereafter	7.2
Total	262.4
Peaker CfDs
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2023	20.3
2024	21.1
2025	17.9
2026	16.0
2027	11.4
Thereafter	64.4
Total	151.1
Transmission Support Commitments
Transmission Support Commitments
2023	17.8
2024	20.7
2025	22.6
2026	22.6
2027	22.6
Thereafter	22.6
Total	128.9
CL&P
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2023	705.6
2024	722.3
2025	709.4
2026	632.6
2027	629.3
Thereafter	2,326.4
Total	5,725.6
CL&P | Renewable Energy Purchase Contracts
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2023	594.8
2024	609.1
2025	610.2
2026	607.6
2027	609.0
Thereafter	2,253.1
Total	5,283.8
CL&P | Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2023	83.5
2024	83.9
2025	72.4
2026	0.1
2027	0.0
Thereafter	0.0
Total	239.9
CL&P | Peaker CfDs
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2023	20.3
2024	21.1
2025	17.9
2026	16.0
2027	11.4
Thereafter	64.4
Total	151.1
CL&P | Transmission Support Commitments
Transmission Support Commitments
2023	7.0
2024	8.2
2025	8.9
2026	8.9
2027	8.9
Thereafter	8.9
Total	50.8
NSTAR Electric
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2023	89.1
2024	281.0
2025	328.2
2026	334.6
2027	340.2
Thereafter	5,535.9
Total	6,909.0
NSTAR Electric | Renewable Energy Purchase Contracts
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2023	79.2
2024	270.0
2025	316.5
2026	322.9
2027	328.6
Thereafter	5,519.8
Total	6,837.0
NSTAR Electric | Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2023	2.9
2024	2.9
2025	2.8
2026	2.8
2027	2.7
Thereafter	7.2
Total	21.3
NSTAR Electric | Transmission Support Commitments
Transmission Support Commitments
2023	7.0
2024	8.1
2025	8.9
2026	8.9
2027	8.9
Thereafter	8.9
Total	50.7
PSNH
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2023	82.8
2024	77.9
2025	32.9
2026	57.3
2027	65.7
Thereafter	373.0
Total	689.6
PSNH | Renewable Energy Purchase Contracts
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2023	77.8
2024	73.5
2025	28.1
2026	52.5
2027	60.9
Thereafter	368.2
Total	661.0
PSNH | Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2023	1.2
2024	0.0
2025	0.0
2026	0.0
2027	0.0
Thereafter	0.0
Total	1.2
PSNH | Transmission Support Commitments
Transmission Support Commitments
2023	3.8
2024	4.4
2025	4.8
2026	4.8
2027	4.8
Thereafter	4.8
Total	$ 27.4