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ACQUISITION OF AQUARION - Narrative (Details) - USD ($)
$ in Millions
Dec. 04, 2017
Jun. 02, 2017
Mar. 31, 2018
Aquarion Water Company      
Business Acquisition [Line Items]      
Consideration transferred   $ 1,675.0  
Payments to acquire businesses $ 880.0 880.0  
Consideration transferred, liabilities incurred   $ 795.0  
Equity interest 745.0    
Aquarion shareholder loan paid at closing $ 135.0    
Line of Credit | Aquarion      
Business Acquisition [Line Items]      
Long-term debt, fair value     $ 7.9