PROPERTY, PLANT, AND EQUIPMENT - Southern Power Useful Lives (Details) - Southern Power - Maximum	12 Months Ended
	Dec. 31, 2019
Natural Gas Generating Facility
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, useful life (years)	45 years
Biomass Generating Facility
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, useful life (years)	40 years
Solar Generating Facility
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, useful life (years)	35 years
Wind Generating Facility
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, useful life (years)	30 years