Segment and Related Information - Schedule of Gas Revenues (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Segment Reporting Information [Line Items]
Total operating revenues	$ 7,823			$ 7,274			$ 22,572	$ 20,383
Other segment items	3,564			3,491			11,377	10,146
Depreciation and amortization	1,422			1,210			4,030	3,537
Earnings from equity method investments	33			31			76	107
Interest expense(e)	755			692			2,343	2,050
Income taxes (benefit)	404			377			973	890
Consolidated Net Income Attributable to Southern Company	1,711			1,535			3,925	3,867
Total assets	153,248						153,248		$ 145,180
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	734			682			3,552	3,220
Other segment items	464			421			2,133	1,866
Depreciation and amortization	176			162			517	475
Earnings from equity method investments	31			34			93	110
Interest expense(e)	94			84			277	250
Income taxes (benefit)	6			11			169	184
Consolidated Net Income Attributable to Southern Company	25	$ 106	$ 418	38	$ 108	$ 409	549	555
Total assets	26,926						26,926		26,177
Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues	7,662			7,104			22,040	19,913
Other segment items	3,396			3,329			10,886	9,700
Depreciation and amortization	1,404			1,193			3,978	3,484
Earnings from equity method investments	33			36			97	114
Interest expense(e)	458			433			1,343	1,293
Income taxes (benefit)	489			447			1,246	1,101
Consolidated Net Income Attributable to Southern Company	1,948			1,738			4,684	4,449
Total assets	151,312						151,312		143,382
Operating Segments \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	734			677			3,549	3,210
Other segment items	460			417			2,129	1,859
Depreciation and amortization	175			161			516	474
Earnings from equity method investments	31			34			93	110
Interest expense(e)	100			84			282	257
Income taxes (benefit)	(5)			6			159	178
Consolidated Net Income Attributable to Southern Company	35			43			556	552
Total assets	28,335						28,335		27,336
Operating Segments \| Gas distribution operations \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	668			616			3,122	2,828
Other segment items	409			366			1,842	1,612
Depreciation and amortization	171			156			502	459
Earnings from equity method investments	0			0			0	0
Interest expense(e)	89			75			252	229
Income taxes (benefit)	(13)			(2)			109	125
Consolidated Net Income Attributable to Southern Company	12			21			417	403
Total assets	25,200						25,200		24,067
Operating Segments \| Gas Pipeline Investments \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	8			8			24	24
Other segment items	1			1			3	3
Depreciation and amortization	1			1			4	4
Earnings from equity method investments	31			34			93	110
Interest expense(e)	10			8			28	26
Income taxes (benefit)	7			8			20	24
Consolidated Net Income Attributable to Southern Company	20			24			62	77
Total assets	1,468						1,468		1,573
Operating Segments \| Gas marketing services \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	58			53			403	358
Other segment items	50			50			284	244
Depreciation and amortization	3			4			10	11
Earnings from equity method investments	0			0			0	0
Interest expense(e)	1			1			2	2
Income taxes (benefit)	1			0			30	29
Consolidated Net Income Attributable to Southern Company	3			(2)			77	72
Total assets	1,667						1,667		1,696
Operating Segments \| All Other \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Consolidated Net Income Attributable to Southern Company				(5)
All Other
Segment Reporting Information [Line Items]
Total operating revenues	202			215			656	598
Other segment items	209			203			611	548
Depreciation and amortization	18			17			52	53
Earnings from equity method investments	0			(5)			(21)	(8)
Interest expense(e)	297			261			1,000	769
Income taxes (benefit)	(85)			(70)			(273)	(211)
Consolidated Net Income Attributable to Southern Company	(237)			(201)			(755)	(569)
Total assets	2,397						2,397		2,371
All Other \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	1			6			11	19
Other segment items	5			5			12	16
Depreciation and amortization	1			1			1	1
Earnings from equity method investments	0			0			0	0
Interest expense(e)	(6)			0			(5)	(7)
Income taxes (benefit)	11			5			10	6
Consolidated Net Income Attributable to Southern Company	(10)						(7)	3
Total assets	10,845						10,845		10,047
Eliminations
Segment Reporting Information [Line Items]
Total operating revenues	(41)			(45)			(124)	(128)
Other segment items	(41)			(41)			(120)	(102)
Depreciation and amortization	0			0			0	0
Earnings from equity method investments	0			0			0	1
Interest expense(e)	0			(2)			0	(12)
Income taxes (benefit)	0			0			0	0
Consolidated Net Income Attributable to Southern Company	0			(2)			(4)	(13)
Total assets	(461)						(461)		(573)
Eliminations \| SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Total operating revenues	(1)			(1)			(8)	(9)
Other segment items	(1)			(1)			(8)	(9)
Depreciation and amortization	0			0			0	0
Earnings from equity method investments	0			0			0	0
Interest expense(e)	0			0			0	0
Income taxes (benefit)	0			0			0	0
Consolidated Net Income Attributable to Southern Company	0			$ 0			0	$ 0
Total assets	$ (12,254)						$ (12,254)		$ (11,206)

SOUTHERN CO 10-Q