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Segment and Related Information - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025 USD ($) state	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) state segment	Sep. 30, 2024 USD ($)
Segment Reporting Information [Line Items]
Number of states in which entity operates | state	3		3
Operating revenues	$ 7,822	$ 7,481	$ 22,142	$ 20,513
Earnings from equity method investments	33	31	76	107
Other segment items	3,564	3,491	$ 11,377	10,146
Traditional Electric Operating Companies
Segment Reporting Information [Line Items]
Number of operating segments | segment			3
Number of reportable segments | segment			1
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Number of reportable segments | segment			1
Operating revenues	417	423	$ 1,212	1,143
SOUTHERN POWER CO | Kay Wind Facility
Segment Reporting Information [Line Items]
Depreciation before tax	112		181
Depreciation after tax	80		130
SOUTHERN POWER CO | Reportable Segment
Segment Reporting Information [Line Items]
Other segment items	$ 332	322	$ 930	834
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Number of states in which entity operates | state	4		4
Number of reportable segments | segment			3
Operating revenues	$ 725	667	$ 3,537	3,117
Earnings from equity method investments	31	34	93	110
Other segment items	$ 464	421	$ 2,133	1,866
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%
MISSISSIPPI POWER CO
Segment Reporting Information [Line Items]
Operating revenues	$ 481	424	$ 1,270	1,131
MISSISSIPPI POWER CO | Reportable Segment
Segment Reporting Information [Line Items]
Other segment items	251	200	686	550
Traditional Electric Operating Companies | Wholesale revenues, affiliates | SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues	112	102	341	280
Traditional Electric Operating Companies | Natural Gas | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	$ 0	$ 0	$ 0	$ 0

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