Segment and Related Information - Narrative (Details) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2025 USD ($) state	Jun. 30, 2024 USD ($)	Jun. 30, 2025 USD ($) segment state	Jun. 30, 2024 USD ($)
Segment Reporting Information [Line Items]
Number of states in which entity operates \| state	3		3
Operating revenues	$ 6,734	$ 6,347	$ 14,328	$ 13,028
Earnings from equity method investments	10	31	43	77
Other segment items	3,617	3,125	$ 7,812	6,656
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	362	352	$ 795	721
SOUTHERN POWER CO \| Kay Wind Facility
Segment Reporting Information [Line Items]
Depreciation before tax	42		69
Depreciation after tax	31		51
SOUTHERN POWER CO \| Reportable Segment
Segment Reporting Information [Line Items]
Other segment items	$ 296	268	$ 599	512
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	$ 972	802	$ 2,811	2,451
Earnings from equity method investments	23	32	62	76
Other segment items	$ 599	478	$ 1,670	1,443
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	$ 381	365	$ 788	708
MISSISSIPPI POWER CO \| Reportable Segment
Segment Reporting Information [Line Items]
Earnings from equity method investments	0	0	0	0
Other segment items	252	221	528	438
Traditional Electric Operating Companies \| Wholesale revenues, affiliates \| SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues	114	86	229	179
Traditional Electric Operating Companies \| Natural Gas \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	$ 0	$ 0	$ 0	$ 0

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