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LEASES - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Lessee, Lease, Description [Line Items] |  |  |
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities | $ 2.1 | $ 0.6 | $ 2.9
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities | $ 2.3 | 0.7 | 2.0
CMA |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities |  | 14.7 |
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities |  | 54.2 |
Minimum |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Renewal period | 1 year |  |
Maximum |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Renewal period | 20 years |  |
The Connecticut Light and Power Company |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities | $ 0.0 | 0.1 | 1.0
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities | $ 0.0 | 0.0 | 0.0
The Connecticut Light and Power Company | Minimum |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Renewal period | 1 year |  |
The Connecticut Light and Power Company | Maximum |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Renewal period | 20 years |  |
NSTAR Electric Company |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities | $ 1.9 | 0.2 | 0.1
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities | $ 0.0 | 0.3 | 0.0
NSTAR Electric Company | Minimum |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Renewal period | 1 year |  |
NSTAR Electric Company | Maximum |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Renewal period | 20 years |  |
Public Service Company of New Hampshire |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities | $ 0.0 | 0.0 | 0.2
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities | $ 0.0 | $ 0.0 | $ 0.0
Public Service Company of New Hampshire | Minimum |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Renewal period | 1 year |  |
Public Service Company of New Hampshire | Maximum |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Renewal period | 20 years |  |

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