Segment and Related Information - Schedule of Business Segment Financial Data (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Total operating revenues	$ 5,748	$ 7,206	$ 12,228	$ 13,854
Net income after dividends on preferred stock	838	1,107	1,700	2,139
Total assets	137,116		137,116		$ 134,891
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	852	1,083	2,728	3,140
Net income after dividends on preferred stock	85	115	393	433
Total assets	24,331		24,331		24,621
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	847	1,080	2,719	3,133
Net income after dividends on preferred stock	86	116	387	425
Total assets	25,460		25,460		25,233
Operating Segments | Gas distribution operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	764	980	2,383	2,782
Net income after dividends on preferred stock	60	92	281	306
Total assets	22,366		22,366		22,040
Operating Segments | Gas Pipeline Investments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	8	8	16	16
Net income after dividends on preferred stock	19	23	50	52
Total assets	1,552		1,552		1,577
Operating Segments | Gas marketing services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	75	92	320	335
Net income after dividends on preferred stock	7	1	56	67
Total assets	1,542		1,542		1,616
Operating Segments | All Other
Segment Reporting Information [Line Items]
Total operating revenues	180	159	346	283
Net income after dividends on preferred stock	(157)	(137)	(311)	(263)
Total assets	3,523		3,523		2,665
Operating Segments | All Other | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	9	10	22	26
Net income after dividends on preferred stock	(1)	(1)	6	8
Total assets	9,606		9,606		8,943
Eliminations
Segment Reporting Information [Line Items]
Total operating revenues	(48)	(42)	(93)	(85)
Net income after dividends on preferred stock	2	(5)	(2)	(12)
Total assets	(946)		(946)		(678)
Eliminations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	(4)	(7)	(13)	(19)
Net income after dividends on preferred stock	0	$ 0	0	$ 0
Total assets	$ (10,735)		$ (10,735)		$ (9,555)