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COMMITMENTS AND CONTINGENCIES - Schedule of Estimated Future Annual Costs of Long term Contractual Agreement (Details) $ in Millions	Dec. 31, 2024 USD ($)
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2025	$ 1,425.0
2026	1,400.7
2027	1,330.3
2028	1,273.0
2029	1,128.6
Thereafter	7,403.8
Total	13,961.4
Renewable Energy Purchase Contracts
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2025	771.8
2026	865.2
2027	919.9
2028	918.0
2029	785.5
Thereafter	6,289.9
Total	10,550.3
Natural Gas Procurement
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2025	532.6
2026	486.1
2027	364.6
2028	308.1
2029	294.9
Thereafter	1,004.4
Total	2,990.7
Capacity and Purchased Power
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2025	75.2
2026	2.9
2027	2.7
2028	2.7
2029	2.3
Thereafter	2.3
Total	88.1
Peaker CfDs
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2025	28.3
2026	27.7
2027	23.1
2028	23.3
2029	24.1
Thereafter	84.6
Total	211.1
Transmission Support Commitments
Transmission Support Commitments
2025	17.1
2026	18.8
2027	20.0
2028	20.9
2029	21.8
Thereafter	22.6
Total	121.2
CL&P
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2025	758.5
2026	707.1
2027	754.7
2028	756.1
2029	621.1
Thereafter	3,567.1
Total	7,164.6
CL&P | Renewable Energy Purchase Contracts
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2025	651.0
2026	671.9
2027	723.7
2028	724.5
2029	588.4
Thereafter	3,473.6
Total	6,833.1
CL&P | Capacity and Purchased Power
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2025	72.4
2026	0.1
2027	0.0
2028	0.0
2029	0.0
Thereafter	0.0
Total	72.5
CL&P | Peaker CfDs
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2025	28.3
2026	27.7
2027	23.1
2028	23.3
2029	24.1
Thereafter	84.6
Total	211.1
CL&P | Transmission Support Commitments
Transmission Support Commitments
2025	6.8
2026	7.4
2027	7.9
2028	8.3
2029	8.6
Thereafter	8.9
Total	47.9
NSTAR Electric
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2025	130.3
2026	203.5
2027	206.8
2028	204.4
2029	208.0
Thereafter	2,827.5
Total	3,780.5
NSTAR Electric | Renewable Energy Purchase Contracts
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2025	120.8
2026	193.3
2027	196.2
2028	193.5
2029	197.1
Thereafter	2,816.3
Total	3,717.2
NSTAR Electric | Capacity and Purchased Power
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2025	2.8
2026	2.8
2027	2.7
2028	2.7
2029	2.3
Thereafter	2.3
Total	15.6
NSTAR Electric | Transmission Support Commitments
Transmission Support Commitments
2025	6.7
2026	7.4
2027	7.9
2028	8.2
2029	8.6
Thereafter	8.9
Total	47.7
PSNH | Transmission Support Commitments
Transmission Support Commitments
2025	3.6
2026	4.0
2027	4.2
2028	4.4
2029	4.6
Thereafter	4.8
Total	$ 25.6

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Amount of the recorded obligation to transfer funds in the future for fixed or minimum amounts or quantities of goods or services at fixed or minimum prices (for example, as in take-or-pay contracts or throughput contracts).

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