Acquisitions and Dispositions - Schedule of Construction Projects (Details) - SOUTHERN POWER CO - MW	1 Months Ended	3 Months Ended
	May 31, 2019	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Aug. 31, 2018	May 31, 2018
Mankato expansion
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)	385			385
PPA Contract Period	20 years
Wild Horse Mountain | Wild Horse Mountain
Business Acquisition [Line Items]
Ownership percentage by parent						100.00%
Reading | Reading
Business Acquisition [Line Items]
Ownership percentage by parent					100.00%
Reading | Reading | Class B Membership Interest
Business Acquisition [Line Items]
Ownership percentage by parent					100.00%
Scenario, Forecast | Wild Horse Mountain
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)			100
PPA Contract Period			20 years
Scenario, Forecast | Reading
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)		200
PPA Contract Period		12 years