COMMITMENTS AND CONTINGENCIES - Schedule of Estimated Future Annual Costs of Long term Contractual Agreement (Details) $ in Millions	Dec. 31, 2021 USD ($)
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2022	$ 1,251.4
2023	1,168.1
2024	1,113.6
2025	1,118.4
2026	1,020.1
Thereafter	5,184.3
Total	10,855.9
Renewable Energy
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2022	755.4
2023	700.7
2024	696.4
2025	718.7
2026	714.3
Thereafter	3,571.4
Total	7,156.9
Natural Gas Procurement
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2022	377.9
2023	323.6
2024	270.5
2025	265.5
2026	250.4
Thereafter	1,517.2
Total	3,005.1
Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2022	76.0
2023	87.1
2024	86.7
2025	75.1
2026	2.9
Thereafter	9.8
Total	337.6
Peaker CfDs
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2022	26.1
2023	38.9
2024	39.4
2025	36.7
2026	29.9
Thereafter	63.3
Total	234.3
Transmission Support Commitments
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2022	16.0
2023	17.8
2024	20.6
2025	22.4
2026	22.6
Thereafter	22.6
Total	122.0
The Connecticut Light and Power Company
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2022	690.7
2023	721.4
2024	723.3
2025	711.7
2026	630.8
Thereafter	2,824.4
Total	6,302.3
The Connecticut Light and Power Company | Renewable Energy
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2022	586.2
2023	592.1
2024	592.0
2025	593.9
2026	591.9
Thereafter	2,752.2
Total	5,708.3
The Connecticut Light and Power Company | Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2022	72.1
2023	83.4
2024	83.8
2025	72.3
2026	0.1
Thereafter	0.0
Total	311.7
The Connecticut Light and Power Company | Peaker CfDs
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2022	26.1
2023	38.9
2024	39.4
2025	36.7
2026	29.9
Thereafter	63.3
Total	234.3
The Connecticut Light and Power Company | Transmission Support Commitments
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2022	6.3
2023	7.0
2024	8.1
2025	8.8
2026	8.9
Thereafter	8.9
Total	48.0
NSTAR Electric Company
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2022	112.2
2023	88.2
2024	86.7
2025	87.8
2026	88.1
Thereafter	511.0
Total	974.0
NSTAR Electric Company | Renewable Energy
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2022	102.9
2023	78.3
2024	75.7
2025	76.1
2026	76.4
Thereafter	492.3
Total	901.7
NSTAR Electric Company | Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2022	3.0
2023	2.9
2024	2.9
2025	2.8
2026	2.8
Thereafter	9.8
Total	24.2
NSTAR Electric Company | Transmission Support Commitments
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2022	6.3
2023	7.0
2024	8.1
2025	8.9
2026	8.9
Thereafter	8.9
Total	48.1
Public Service Company of New Hampshire
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2022	70.6
2023	34.9
2024	33.1
2025	53.4
2026	50.8
Thereafter	331.7
Total	574.5
Public Service Company of New Hampshire | Renewable Energy
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2022	66.3
2023	30.3
2024	28.7
2025	48.7
2026	46.0
Thereafter	326.9
Total	546.9
Public Service Company of New Hampshire | Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2022	0.9
2023	0.8
2024	0.0
2025	0.0
2026	0.0
Thereafter	0.0
Total	1.7
Public Service Company of New Hampshire | Transmission Support Commitments
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2022	3.4
2023	3.8
2024	4.4
2025	4.7
2026	4.8
Thereafter	4.8
Total	$ 25.9