SHORT-TERM AND LONG-TERM DEBT - Long-Term Debt Issuances (Details) - Senior Notes [Member]	Mar. 31, 2017 USD ($)
Eversource Parent [Member] \| Series K Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 300,000,000
Interest rate stated percentage	2.75%
The Connecticut Light And Power Company [Member] \| 2017 Series A First and Refunding Mortgage Bonds Due 2027 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 300,000,000
Interest rate stated percentage	3.20%

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant