SHORT-TERM AND LONG-TERM DEBT - Schedule of Commercial Paper Program (Details) - Commercial Paper - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
NSTAR Electric Company
Debt Instrument [Line Items]
Borrowings Outstanding	$ 367.0	$ 234.0
Available Borrowing Capacity	$ 283.0	$ 416.0
Weighted-Average Interest Rate	1.75%	1.55%
Eversource Parent
Debt Instrument [Line Items]
Borrowings Outstanding	$ 682.3	$ 979.3
Available Borrowing Capacity	$ 767.7	$ 470.7
Weighted-Average Interest Rate	2.31%	1.86%

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19)(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16)(a)(1))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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