COMMITMENTS AND CONTINGENCIES - Schedule of Guarantees and Indemnifications (Details) $ in Millions	Dec. 31, 2018 USD ($)
Access Northeast Project Capital Contributions Guaranty
Guarantor Obligations [Line Items]
Maximum Exposure	$ 184.9
Surety Bonds
Guarantor Obligations [Line Items]
Maximum Exposure	41.9
Lease Payments for Real Estate
Guarantor Obligations [Line Items]
Maximum Exposure	6.3
Bay State Wind LLC
Guarantor Obligations [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=115931803&loc=d3e12069-110248

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