Acquisitions and Dispositions - Schedule of Construction Projects (Details) - SOUTHERN POWER CO - MW	1 Months Ended		3 Months Ended
	Jul. 31, 2018	Mar. 31, 2018	Dec. 31, 2019	Jun. 30, 2019	Aug. 07, 2018	Jun. 30, 2018	May 31, 2018	Jul. 31, 2017
Gaskell West 1
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)						20
PPA Contract Period		20 years
Cactus Flats
Business Acquisition [Line Items]
Southern Power Percentage Ownership								100.00%
Wildhorse
Business Acquisition [Line Items]
Southern Power Percentage Ownership							100.00%
Scenario, Forecast | Cactus Flats
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)	148
Scenario, Forecast | Mankato
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)				345
PPA Contract Period				20 years
Scenario, Forecast | Wildhorse
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)			100
PPA Contract Period			20 years
Minimum | Scenario, Forecast | Cactus Flats
Business Acquisition [Line Items]
PPA Contract Period	12 years
Maximum | Scenario, Forecast | Cactus Flats
Business Acquisition [Line Items]
PPA Contract Period	15 years
Common Class B | Gaskell West 1
Business Acquisition [Line Items]
Southern Power Percentage Ownership						100.00%
Class B Membership Interest | Gaskell West 1
Business Acquisition [Line Items]
Southern Power Percentage Ownership						100.00%
Class B Membership Interest | Cactus Flats
Business Acquisition [Line Items]
Southern Power Percentage Ownership							100.00%
Subsequent Event | Class B Membership Interest | Cactus Flats
Business Acquisition [Line Items]
Southern Power Percentage Ownership					100.00%