Acquisitions and Dispositions - Schedule of Business Acquisitions and Construction Projects (Details) - SOUTHERN POWER CO - MW	1 Months Ended		3 Months Ended		6 Months Ended
	Jul. 31, 2018	Mar. 31, 2018	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Sep. 30, 2018	Aug. 31, 2018	May 31, 2018	Jul. 31, 2017
Gaskell West 1
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)						20
PPA Contract Period		20 years
Gaskell West 1 | Gaskell West 1 | Common Class B
Business Acquisition [Line Items]
Southern Power Percentage Ownership						100.00%
Gaskell West 1 | Gaskell West 1 | Class B Membership Interest
Business Acquisition [Line Items]
Southern Power Percentage Ownership						100.00%
Cactus Flats
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)	148
Cactus Flats | Minimum
Business Acquisition [Line Items]
PPA Contract Period	12 years
Cactus Flats | Maximum
Business Acquisition [Line Items]
PPA Contract Period	15 years
Cactus Flats | Cactus Flats
Business Acquisition [Line Items]
Southern Power Percentage Ownership									100.00%
Cactus Flats | Cactus Flats | Class B Membership Interest
Business Acquisition [Line Items]
Southern Power Percentage Ownership							100.00%
Mankato | Scenario, Forecast
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)					385
PPA Contract Period					20 years
Wild Horse Mountain | Scenario, Forecast
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)				100
PPA Contract Period				20 years
Wild Horse Mountain | Wild Horse Mountain
Business Acquisition [Line Items]
Southern Power Percentage Ownership								100.00%
Wild Horse Mountain | Wild Horse Mountain | Class B Membership Interest
Business Acquisition [Line Items]
Southern Power Percentage Ownership								100.00%
Reading | Scenario, Forecast
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)			200
PPA Contract Period			12 years
Reading | Reading
Business Acquisition [Line Items]
Southern Power Percentage Ownership							100.00%
Reading | Reading | Class B Membership Interest
Business Acquisition [Line Items]
Southern Power Percentage Ownership							100.00%