Segment and Related Information - Schedule of Financial Data for Business Segments (Details) - USD ($) $ in Millions		3 Months Ended					9 Months Ended
	Jul. 01, 2021	Sep. 30, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Operating revenues			$ 6,238			$ 5,620	$ 17,346	$ 15,258
Segment net income (loss)			1,101			1,251	2,608	2,732
Goodwill		$ 5,280	5,280				5,280		$ 5,280
Assets held for sale		51	51				51		60
Total assets		127,861	127,861				127,861		122,935
Gain on sale							171	36
Estimated loss on Plant Vogtle Units 3 and 4			264			0	772	149
Impairment of leveraged leases			0			0	7	154
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues			679			523	1,610	1,337
Total assets		13,611	13,611				13,611		13,235
Gain on sale							39	39
SOUTHERN POWER CO | Wind Generating Facility
Segment Reporting Information [Line Items]
Gain on sale							37
Gain on sale, net of tax							28
SOUTHERN POWER CO | Disposal Group, Disposed of by Sale | Plant Mankato
Segment Reporting Information [Line Items]
Gain on sale								39
Gain on sale, net of tax								23
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			623			477	2,994	2,362
Segment net income (loss)			56			14	389	360
Goodwill		5,015	5,015				5,015		5,015
Total assets		22,958	22,958				22,958		22,630
Gain on sale							127	(2)
Deferred tax expense, increase from change in appointment rate			85				85
Asset impairment charges							84	0
SOUTHERN Co GAS | Disposal Group, Disposed of by Sale | Sequent
Segment Reporting Information [Line Items]
Gain on sale	$ 121
Gain on sale, net of tax	$ 93
Deferred tax expense, increase from change in appointment rate		85
GEORGIA POWER CO
Segment Reporting Information [Line Items]
Operating revenues			2,856			2,617	7,050	6,371
Total assets		48,932	48,932				48,932		47,080
Estimated loss on Plant Vogtle Units 3 and 4			264	$ 460	$ 48	0	772	149
Estimated loss on Plant Vogtle Units 3 and 4, net of tax			197	$ 343	$ 36		576	111
Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues			5,527			5,049	14,051	12,628
Segment net income (loss)			1,163			1,358	2,563	2,783
Goodwill		2	2				2		2
Assets held for sale		3	3				3		5
Total assets		101,960	101,960				101,960		98,041
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			623			477	2,994	2,362
All Other
Segment Reporting Information [Line Items]
Impairment of leveraged leases							7	154
Impairment of leveraged lease, net of tax							6	74
Gas distribution operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Goodwill		4,034	4,034				4,034		4,034
Wholesale Gas Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			0			(51)	188	(19)
Gas marketing services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Goodwill		981	981				981		981
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			616			475	2,989	2,363
Segment net income (loss)			147			21	479	372
Total assets		23,763	23,763				23,763		23,040
Operating Segments | Traditional Electric Operating Companies | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues			5,018			4,629	12,813	11,576
Segment net income (loss)			1,085			1,284	2,352	2,571
Goodwill		0	0				0		0
Assets held for sale		3	3				3		5
Total assets		89,057	89,057				89,057		85,486
Operating Segments | SOUTHERN POWER CO | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues			679			523	1,610	1,337
Segment net income (loss)			78			74	211	212
Goodwill		2	2				2		2
Assets held for sale		0	0				0		0
Total assets		13,611	13,611				13,611		13,235
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			623			477	2,994	2,362
Segment net income (loss)			56			14	389	360
Goodwill		5,015	5,015				5,015		5,015
Assets held for sale		0	0				0		0
Total assets		22,958	22,958				22,958		22,630
Operating Segments | All Other
Segment Reporting Information [Line Items]
Operating revenues			124			132	412	380
Segment net income (loss)			(121)			(122)	(338)	(420)
Goodwill		263	263				263		263
Assets held for sale		48	48				48		55
Total assets		3,704	3,704				3,704		3,168
Operating Segments | All Other | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			11			8	29	24
Segment net income (loss)			(91)			(7)	(90)	(12)
Total assets		11,387	11,387				11,387		11,336
Operating Segments | Gas distribution operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			556			479	2,466	2,086
Segment net income (loss)			45			46	308	284
Total assets		20,619	20,619				20,619		19,090
Operating Segments | Gas Pipeline Investments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			8			8	24	24
Segment net income (loss)			10			23	3	74
Total assets		1,478	1,478				1,478		1,597
Operating Segments | Wholesale Gas Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			0			(51)	188	(19)
Segment net income (loss)			94			(45)	108	(45)
Total assets		132	132				132		850
Operating Segments | Gas marketing services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			52			39	311	272
Segment net income (loss)			(2)			(3)	60	59
Total assets		1,534	1,534				1,534		1,503
Eliminations
Segment Reporting Information [Line Items]
Operating revenues			(36)			(38)	(111)	(112)
Segment net income (loss)			3			1	(6)	9
Goodwill		0	0				0		0
Assets held for sale		0	0				0		0
Total assets		(761)	(761)				(761)		(904)
Eliminations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues			(4)			(6)	(24)	(25)
Segment net income (loss)			0			0	0	0
Total assets		(12,192)	(12,192)				(12,192)		(11,746)
Eliminations | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues			(170)			(103)	(372)	(285)
Segment net income (loss)			0			$ 0	0	$ 0
Goodwill		0	0				0		0
Assets held for sale		0	0				0		0
Total assets		$ (708)	$ (708)				$ (708)		$ (680)