ACQUISITIONS AND DISPOSITIONS - Schedule of Acquisitions (Details) - Southern Power $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2018 MW	Dec. 31, 2019 USD ($) MW	Dec. 31, 2018
DSGP
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)		28
PPA Contract Period		15 years
Payments to acquire businesses | $		$ 167
Results of operations, percentage consolidated		100.00%
Noncontrolling interest, approximate nameplate capacity (in MW)		10
Approximate nameplate capacity, repowered amount (in MW)		18
Fuel cells, before repower, carrying value | $		$ 55
Gaskell West 1
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)	20
PPA Contract Period	20 years
Results of operations, percentage consolidated			100.00%
DSGP | Class B Membership Interest | DSGP
Business Acquisition [Line Items]
Ownership Percentage		100.00%
Gaskell West 1 | Class B Membership Interest | Gaskell West 1
Business Acquisition [Line Items]
Ownership Percentage	100.00%