Estimate of possible loss for each 10 basis point change to base ROE

No definition available.

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- Definition

Loss Contingency, Percentage of Base ROE Challenged by Complainants

+ References

No definition available.

+ Details

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- Definition

Loss Contingency, Basis Spread

+ References

No definition available.

+ Details

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- Definition

Loss Contingency, Maximum percentage of ROE for incentive projects

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No definition available.

+ Details

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- Definition

Loss Contingency, Percentage of ROE for Any Incentive Project

+ References

No definition available.

+ Details

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- Definition

Loss Contingency, Period of Billing of Reinstated ROE

+ References

No definition available.

+ Details

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- Definition

Loss Contingency, Period of Complaint

+ References

No definition available.

+ Details

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- Definition

Percentage of Base ROE of Complaint Period

+ References

No definition available.

+ Details

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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.

+ Details

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- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14557-108349

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COMMITMENTS AND CONTINGENCIES - FERC ROE Complaints (Details) - USD ($) $ in Millions				6 Months Ended	15 Months Ended	30 Months Ended
	Jun. 08, 2017	Apr. 14, 2017	Apr. 29, 2016	Jun. 30, 2017	Mar. 26, 2014	Apr. 14, 2017
FERC ROE First, Second and Third Complaints [Member]
Loss Contingencies [Line Items]
Base ROE percentage challenged by complainants	11.14%			11.14%
Percentage of maximum ROE for any incentive project	13.50%
Period of billing of reinstated ROE				60 days
FERC ROE Complaints [Member]
Loss Contingencies [Line Items]
Period of complaint				15 months
Basis point change				10.00%
Estimate of possible loss for each 10 basis point change to base ROE				$ 3.0
FERC ROE Fourth Complaint [Member]
Loss Contingencies [Line Items]
Base ROE percentage of complaint period			10.57%
Maximum percentage cap of ROE for incentive projects			11.74%
Loss contingency, estimate of possible earnings impact				$ 0.0
FERC ROE First Complaint [Member]
Loss Contingencies [Line Items]
Base ROE percentage challenged by complainants		11.14%		10.57%
Percentage of maximum ROE for any incentive project				11.74%		11.74%
Loss contingency, estimate of possible earnings impact				$ 0.0
FERC ROE Second Complaint [Member]
Loss Contingencies [Line Items]
Base ROE percentage of complaint period					10.57%
Percentage of maximum ROE for any incentive project					11.74%
Loss contingency, estimate of possible earnings impact				39.1
The Connecticut Light And Power Company [Member] \| FERC ROE Second Complaint [Member]
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact				21.4
NSTAR Electric Company [Member] \| FERC ROE Second Complaint [Member]
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact				8.5
Public Service Company Of New Hampshire [Member] \| FERC ROE Second Complaint [Member]
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact				3.1
Western Massachusetts Electric Company [Member] \| FERC ROE Second Complaint [Member]
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact				$ 6.1