ACQUISITIONS AND DISPOSITIONS - Schedule of Acquisitions (Details) - Southern Power - MW	1 Months Ended		12 Months Ended
	May 31, 2020	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2020
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)					300
Beech Ridge II
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)	56
PPA Contract Period	12 years
DSGP
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)				28
PPA Contract Period				15 years
Noncontrolling interest, approximate nameplate capacity (in MW)				10
Approximate nameplate capacity, repowered amount (in MW)			18
Gaskell West 1
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)		20
PPA Contract Period		20 years
Beech Ridge II | Beech Ridge II
Business Acquisition [Line Items]
Ownership Percentage	100.00%
DSGP | DSGP
Business Acquisition [Line Items]
Ownership Percentage				100.00%
Gaskell West 1 | Gaskell West 1
Business Acquisition [Line Items]
Ownership Percentage		100.00%