COMMITMENTS AND CONTINGENCIES - Summary of Exposure to Guarantees and Indemnifications (Details) $ in Millions	Sep. 30, 2019 USD ($)
Various - Surety Bonds
Loss Contingencies [Line Items]
Maximum exposure	$ 34.3
Rocky River Realty Company and Eversource Service - Lease Payments for Real Estate
Loss Contingencies [Line Items]
Maximum exposure	6.8
Bay State Wind LLC - Real Estate Purchase
Loss Contingencies [Line Items]
Maximum exposure	$ 2.5

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=118943654&loc=d3e12069-110248

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