SEGMENT AND RELATED INFORMATION - Gas Revenues (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	Jul. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Operating revenues				$ 25,253	$ 29,279	$ 23,113
Depreciation and amortization				4,525	3,663	3,565
Operating income (loss)				5,826	5,370	3,698
Earnings from equity method investments				144	151	76
Interest expense				2,446	2,022	1,837
Income taxes (benefit)				496	795	267
Segment net income (loss)				3,976	3,524	2,393
Total assets				139,331	134,891	127,534
Impairment charges				0	251	2
Southern Company Gas
Segment Reporting Information [Line Items]
Operating revenues				4,702	5,962	4,380
Depreciation and amortization				582	559	536
Operating income (loss)				939	814	1,055
Earnings from equity method investments				140	148	50
Interest expense				310	263	238
Income taxes (benefit)				211	180	275
Segment net income (loss)				615	572	539
Total assets				25,083	24,621	23,560
Impairment charges				0	131	0
Gain on dispositions, net				7	4	127
Southern Company Gas | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Sequent
Segment Reporting Information [Line Items]
Deferred tax expense, increase from change in appointment rate	$ 85			85		85
Gain on dispositions, net	121			121		121
Gain (loss) on dispositions, after tax	$ 92			92		92
Southern Company Gas | PennEast Pipeline
Segment Reporting Information [Line Items]
Earnings from equity method investments				0	0	(81)
Income taxes (benefit)						7
Impairment charges		$ 2	$ 82	84		84
Impairment charges, after tax		$ 2	$ 58	67		67
Operating Segments | Southern Company Gas
Segment Reporting Information [Line Items]
Operating revenues				4,685	5,937	4,374
Depreciation and amortization				581	537	505
Operating income (loss)				956	957	1,095
Earnings from equity method investments				140	148	50
Interest expense				310	259	237
Income taxes (benefit)				195	217	213
Segment net income (loss)				630	671	626
Total assets				26,055	25,233	23,971
Intersegment Eliminations
Segment Reporting Information [Line Items]
Operating revenues				(165)	(149)	(149)
Depreciation and amortization				0	0	0
Earnings from equity method investments				0	0	1
Interest expense				(17)	(2)	0
Income taxes (benefit)				0	0	0
Segment net income (loss)				2	(9)	(9)
Total assets				(843)	(678)	(775)
Intersegment Eliminations | Southern Company Gas
Segment Reporting Information [Line Items]
Operating revenues				(19)	(30)	(32)
Depreciation and amortization				0	0	0
Operating income (loss)				(13)	(8)	0
Earnings from equity method investments				0	0	0
Interest expense				0	0	0
Income taxes (benefit)				0	0	0
Segment net income (loss)				0	0	0
Total assets				(10,647)	(9,555)	(12,525)
Southern Company Gas
Segment Reporting Information [Line Items]
Operating revenues				4,702	5,962	4,380
Southern Company Gas | Gas distribution operations
Segment Reporting Information [Line Items]
Operating revenues				4,090	5,240	3,656
Southern Company Gas | Gas marketing services
Segment Reporting Information [Line Items]
Operating revenues				548	638	475
Southern Company Gas | Other Gas Revenue
Segment Reporting Information [Line Items]
Operating revenues				64	84	249
Southern Company Gas | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues				4,702	5,962	4,380
Depreciation and amortization				582	559	536
Earnings from equity method investments				140	148	50
Interest expense				310	263	238
Income taxes (benefit)				211	180	275
Segment net income (loss)				615	572	539
Total assets				25,083	24,621	23,560
Wholesale gas services | Operating Segments | Southern Company Gas
Segment Reporting Information [Line Items]
Operating revenues				0	0	188
Depreciation and amortization				0	0	0
Operating income (loss)				0	0	241
Earnings from equity method investments				0	0	0
Interest expense					0	2
Income taxes (benefit)				0	0	32
Segment net income (loss)				0	0	107
Total assets				0	0	31
Less Gross Gas Costs						3,783
Wholesale gas services | Operating Segments | Third Party Gross Revenues | Southern Company Gas
Segment Reporting Information [Line Items]
Operating revenues						3,881
Wholesale gas services | Operating Segments | Intercompany Revenues | Southern Company Gas
Segment Reporting Information [Line Items]
Operating revenues						90
Wholesale gas services | Operating Segments | Total Gross Revenues | Southern Company Gas
Segment Reporting Information [Line Items]
Operating revenues						3,971
Gas distribution operations | Operating Segments | Southern Company Gas
Segment Reporting Information [Line Items]
Operating revenues				4,105	5,267	3,679
Depreciation and amortization				561	516	482
Operating income (loss)				804	803	708
Earnings from equity method investments				0	0	0
Interest expense				275	229	207
Income taxes (benefit)				126	145	120
Segment net income (loss)				441	470	412
Total assets				22,906	22,040	20,917
Gas Pipeline Investments | Operating Segments | Southern Company Gas
Segment Reporting Information [Line Items]
Operating revenues				32	32	32
Depreciation and amortization				5	5	5
Operating income (loss)				22	21	21
Earnings from equity method investments				140	148	50
Interest expense				32	27	25
Income taxes (benefit)				32	35	27
Segment net income (loss)				98	107	19
Total assets				1,534	1,577	1,467
Gas marketing services | Operating Segments | Southern Company Gas
Segment Reporting Information [Line Items]
Operating revenues				548	638	475
Depreciation and amortization				15	16	18
Operating income (loss)				130	133	125
Earnings from equity method investments				0	0	0
Interest expense				3	3	3
Income taxes (benefit)				37	37	34
Segment net income (loss)				91	94	88
Total assets				1,615	1,616	1,556
All Other | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues				718	593	582
Depreciation and amortization				78	75	76
Earnings from equity method investments				5	3	24
Interest expense				879	694	631
Income taxes (benefit)				(298)	(233)	(227)
Segment net income (loss)				(635)	(711)	(384)
Total assets				2,446	2,665	2,975
All Other | Operating Segments | Southern Company Gas
Segment Reporting Information [Line Items]
Operating revenues				36	55	38
Depreciation and amortization				1	22	31
Operating income (loss)				(4)	(135)	(40)
Earnings from equity method investments				0	0	0
Interest expense				0	4	1
Income taxes (benefit)				16	(37)	62
Segment net income (loss)				(15)	(99)	(87)
Total assets				$ 9,675	$ 8,943	$ 12,114