EMPLOYEE BENEFITS - Schedule of Long-term Rates of Return on Pension and PBOP (Details)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Defined Contribution Plan Disclosure [Line Items]
Long-term rate for Aquarion plans	0.07
Defined Benefit Plan, Equity Securities, US
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	15.00%	21.50%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	8.50%	8.50%
Defined Benefit Plan, Debt Security, Public High Yield Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	4.00%	4.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	6.50%	6.50%
Defined Benefit Plan, Debt Security, Private Debt
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	15.00%	15.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	9.00%	9.00%
Defined Benefit Plan, Debt Security, Emerging Markets Debt
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	0.00%	2.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	0.00%	6.50%
Defined Benefit Plan, Equity Securities, Emerging Markets
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	4.00%	4.50%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	10.00%	10.00%
Fixed Income Securities
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	13.00%	11.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	4.00%	4.00%
Defined Benefit Plan, Equity Securities, Global
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	10.00%	0.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	8.75%	0.00%
Defined Benefit Plan, Equity Securities, Non-US
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	8.00%	11.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	8.50%	8.50%
Private Equity
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	15.00%	15.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	12.00%	12.00%
Real Assets
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	16.00%	12.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	7.50%	7.50%
Hedge Funds
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	0.00%	4.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	0.00%	6.00%

Description of basis used to determine overall expected long-term rate-of-return assumption for plan asset of defined benefit plan. Includes, but is not limited to, approach used, and extent approach was based on historical return and adjustment made to reflect expectation of future return.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(iii)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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