COMMITMENTS AND CONTINGENCIES - Non-Cancellable Commitments under Purchase Commitment Contracts (Details) $ in Millions	3 Months Ended
Mar. 31, 2022 USD ($) megawatt
Offshore Wind Project
Unrecorded Unconditional Purchase Obligation [Line Items]
Contract term	20 years
Energy capacity (in MW) \| megawatt	800
Renewable Energy \| NSTAR Electric
Unrecorded Unconditional Purchase Obligation [Line Items]
2022	$ 75.6
2023	78.3
2024	269.4
2025	315.8
2026	322.1
Thereafter	5,812.2
Total	6,873.4
Renewable Energy \| NSTAR Electric \| Massachusetts Clean Energy 83D Contract
Unrecorded Unconditional Purchase Obligation [Line Items]
Total	$ 6,000.0
Contract term	20 years
Renewable Energy \| NSTAR Electric \| Minimum \| Massachusetts Clean Energy 83D Contract
Unrecorded Unconditional Purchase Obligation [Line Items]
Estimated costs	$ 240.0
Renewable Energy \| NSTAR Electric \| Maximum \| Massachusetts Clean Energy 83D Contract
Unrecorded Unconditional Purchase Obligation [Line Items]
Estimated costs	$ 375.0

Contractual Obligation, Term Of Contract

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- Definition

Long-Term Purchase Commitment, Energy Production Capacity

+ References

No definition available.

+ Details

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- Definition

Unrecorded Unconditional Purchase Obligation, Annual Amount

+ References

No definition available.

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- Definition

Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123406679&loc=d3e25336-109308

+ Details

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- Definition

Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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- Definition

Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

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- Definition

Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

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- Definition

Amount of the unrecorded 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).

+ References

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- Definition

Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123406679&loc=d3e25336-109308

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- Definition

Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid in remainder of current fiscal year.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Term of the unrecognized unconditional purchase obligation, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123406679&loc=d3e25336-109308

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