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ACQUISITIONS - BISHOP HILL III ACQUISITION (Details) - Bishop Hill III Wind Energy Center
$ in Millions
 1 Months Ended
Jun. 30, 2018
Jun. 27, 2018
USD ($)
MW
Business Acquisition [Line Items]    
WEC's ownership interest in Bishop Hill III Wind Energy Center   80.00%
Capacity of Bishop Hill III Wind Energy Center | MW   132
Acquisition purchase price | $   $ 148.0
Duration of offtake agreement for the sale of energy produced 22 years  
Bonus depreciation percentage   100.00%