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Segment and Related Information - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($) state	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) state segment	Sep. 30, 2022 USD ($)
Segment Reporting Information [Line Items]
Number of states in which entity operates \| state	3		3
Operating revenues	$ 7,107	$ 7,116	$ 18,886	$ 19,599
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues	$ 480	1,010	$ 1,248	2,157
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Number of states in which entity operates \| state	4		4
Operating revenues	$ 674	843	$ 3,338	3,948
Number of reportable segments \| segment			3
SOUTHERN Co GAS \| Southern Natural Gas Company, LLC
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	50.00%		50.00%
SOUTHERN Co GAS \| Dalton Pipeline
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	50.00%		50.00%
Traditional Electric Operating Companies \| Wholesale revenues, affiliates \| SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues	$ 156	336	$ 406	673
Traditional Electric Operating Companies \| Natural Gas \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	$ 0	$ 0	$ 0	$ 0