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Segment and Related Information - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2026 USD ($) state segment	Mar. 31, 2025 USD ($)
Segment Reporting Information [Line Items]
Number of states in which entity operates | state	3
Operating revenues	$ 8,040	$ 7,591
Earnings from equity method investments	50	32
Other segment items	$ 4,665	4,193
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	$ 523	432
Earnings from equity method investments	0	0
SOUTHERN POWER CO | Kay Wind Facility
Segment Reporting Information [Line Items]
Depreciation before tax	154	27
Depreciation after tax	120	20
SOUTHERN POWER CO | Reportable Segment
Segment Reporting Information [Line Items]
Other segment items	$ 442	303
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Number of states in which entity operates | state	4
Number of reportable segments | segment	3
Operating revenues	$ 2,174	1,840
Earnings from equity method investments	46	39
Other segment items	$ 1,357	1,069
SOUTHERN Co GAS | Southern Natural Gas Company, LLC
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	50.00%
SOUTHERN Co GAS | Dalton Pipeline
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	50.00%
MISSISSIPPI POWER CO
Segment Reporting Information [Line Items]
Operating revenues	$ 464	406
MISSISSIPPI POWER CO | Reportable Segment
Segment Reporting Information [Line Items]
Other segment items	251	218
Traditional Electric Operating Companies | Wholesale revenues, affiliates | SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues	$ 100	$ 116

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