ACQUISITION OF AQUARION AND GOODWILL - Narrative (Details) - USD ($)			12 Months Ended
	Dec. 04, 2017	Oct. 01, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2018
Business Acquisition [Line Items]
Acquisition of Aquarion			$ 0	$ 877,652,000	$ 0
Operating Revenues				15,900,000
Pre-Tax Income				1,100,000
Goodwill			4,427,266,000	4,427,266,000
Impairment loss		$ 0
Aquarion Water Company
Business Acquisition [Line Items]
Consideration transferred	$ 1,675,000,000
Acquisition of Aquarion	880,000,000
Consideration transferred, liabilities incurred	795,000,000
Equity interest	745,000,000
Aquarion shareholder loan paid at closing	135,000,000
Operating Revenues				$ 7,947,700,000	$ 7,849,000,000
Goodwill	$ 900,000,000		$ 907,900,000
Line of Credit | Aquarion
Business Acquisition [Line Items]
Long-term Debt, Fair Value						$ 7,900,000