INTRODUCTION - Intangibles, Amortization (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 12
Decrease in operating revenues	6
SOUTHERN POWER CO
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	5
SOUTHERN Co GAS
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	5
Gas Marketing Services | SOUTHERN Co GAS
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	4
Wholesale Gas Services | SOUTHERN Co GAS
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 1