Acquisitions - Schedule of Construction Projects (Details) - SOUTHERN POWER CO - MW		1 Months Ended		3 Months Ended
	Jan. 06, 2017	Apr. 30, 2017	Mar. 31, 2017	Jun. 30, 2019	Jun. 30, 2017
Bethel
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)	276
Southern Power Percentage Ownership	100.00%
PPA Contract Period	12 years
East Pecos
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)					120
PPA Contract Period			15 years
Lamesa
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)					102
PPA Contract Period		15 years
Scenario, Forecast | Mankato
Business Acquisition [Line Items]
Approximate Nameplate Capacity (MW)				345
PPA Contract Period				20 years