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

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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.

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- Definition

Loss Contingency, Maximum percentage of ROE for incentive projects

+ References

No definition available.

+ Details

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- Definition

Loss Contingency, Percentage of ROE for Any Incentive Project

+ References

No definition available.

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- Definition

Loss Contingency, Period of Complaint

+ References

No definition available.

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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						3 Months Ended	15 Months Ended	30 Months Ended
	Mar. 27, 2018	Oct. 06, 2017	Jun. 08, 2017	Apr. 14, 2017	Apr. 29, 2016	Mar. 31, 2018	Mar. 26, 2014	Apr. 14, 2017
FERC ROE First, Second and Third Complaints
Loss Contingencies [Line Items]
Base ROE percentage challenged by complainants			11.14%			11.14%
Percentage of maximum ROE for any incentive project			13.50%
FERC ROE Complaints
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
Loss Contingencies [Line Items]
Base ROE percentage of complaint period	10.57%				10.57%
Maximum percentage cap of ROE for incentive projects	11.74%				11.74%
Percentage of maximum ROE for any incentive project		10.57%
Loss contingency, estimate of possible earnings impact						0.0
FERC ROE First Complaint
Loss Contingencies [Line Items]
Base ROE percentage challenged by complainants				11.14%
Percentage of maximum ROE for any incentive project								11.74%
Loss contingency, estimate of possible earnings impact						0.0
FERC ROE Second Complaint
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
NSTAR Electric Company \| FERC ROE Second Complaint
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact						$ 14.6