Segment and Related Information - Schedule of Business Segment Financial Data (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Total operating revenues	$ 6,980	$ 8,378	$ 19,208	$ 22,232
Net income after dividends on preferred stock	1,422	1,472	3,121	3,611
Total assets	138,321		138,321		$ 134,891
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	689	857	3,417	3,998
Net income after dividends on preferred stock	82	83	475	516
Total assets	24,823		24,823		24,621
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Total operating revenues	653	1,180	1,686	2,618
Net income after dividends on preferred stock	100	95	288	265
Total assets	13,090		13,090		13,081
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	683	844	3,402	3,977
Net income after dividends on preferred stock	96	81	484	506
Total assets	25,686		25,686		25,233
Operating Segments | Gas distribution operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	619	751	3,002	3,533
Net income after dividends on preferred stock	70	59	352	365
Total assets	22,625		22,625		22,040
Operating Segments | Gas Pipeline Investments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	8	8	24	24
Net income after dividends on preferred stock	24	24	73	76
Total assets	1,542		1,542		1,577
Operating Segments | Gas marketing services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	56	85	376	420
Net income after dividends on preferred stock	2	(2)	59	65
Total assets	1,519		1,519		1,616
Operating Segments | All Other
Segment Reporting Information [Line Items]
Total operating revenues	154	135	499	418
Net income after dividends on preferred stock	(179)	(152)	(490)	(415)
Total assets	2,370		2,370		2,665
Operating Segments | All Other | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	8	16	30	43
Net income after dividends on preferred stock	(14)	2	(9)	10
Total assets	9,795		9,795		8,943
Eliminations
Segment Reporting Information [Line Items]
Total operating revenues	(30)	(41)	(122)	(127)
Net income after dividends on preferred stock	0	1	(4)	(11)
Total assets	(858)		(858)		(678)
Eliminations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	(2)	(3)	(15)	(22)
Net income after dividends on preferred stock	0	$ 0	0	$ 0
Total assets	$ (10,658)		$ (10,658)		$ (9,555)