Segment and Related Information - Schedule of Financial Data for Business Segments (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Operating revenues	$ 5,198		$ 4,620	$ 11,108	$ 9,638
Segment net income (loss)	372		612	1,508	1,480
Goodwill	5,280			5,280		$ 5,280
Assets held for sale	787			787		60
Total assets	125,907			125,907		122,935
Estimated loss on Plant Vogtle Units 3 and 4	460		149	508	149
Impairment of leveraged leases	7		154	7	154
GEORGIA POWER CO
Segment Reporting Information [Line Items]
Operating revenues	2,225		1,928	4,195	3,754
Total assets	47,625			47,625		47,080
Estimated loss on Plant Vogtle Units 3 and 4	460	$ 48	149	508	149
Estimated loss on Plant Vogtle Units 3 and 4, net of tax	343	$ 36	111	379	111
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues	490		439	930	814
Total assets	13,708			13,708		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	677		636	2,371	1,885
Segment net income (loss)	(65)		71	333	346
Goodwill	5,015			5,015		5,015
Assets held for sale	736			736		0
Total assets	23,235			23,235		22,630
Asset impairment charges				82	0
Asset impairment charges, net of tax				58
Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	4,407		3,884	8,524	7,579
Segment net income (loss)	547		708	1,400	1,425
Goodwill	2			2		2
Assets held for sale	2			2		5
Total assets	100,345			100,345		98,041
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	677		636	2,371	1,885
All Other
Segment Reporting Information [Line Items]
Impairment of leveraged leases	7		154	7	154
Impairment of leveraged lease, net of tax	6		74	6	74
Gas distribution operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Goodwill	4,034			4,034		4,034
Wholesale Gas Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	(110)		(19)	188	32
Gas marketing services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Goodwill	981			981		981
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	672		632	2,373	1,888
Segment net income (loss)	(62)		77	332	351
Total assets	24,030			24,030		23,040
Operating Segments | Traditional Electric Operating Companies | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	4,031		3,539	7,795	6,946
Segment net income (loss)	511		645	1,267	1,287
Goodwill	0			0		0
Assets held for sale	2			2		5
Total assets	87,330			87,330		85,486
Operating Segments | SOUTHERN POWER CO | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	490		439	930	814
Segment net income (loss)	36		63	133	138
Goodwill	2			2		2
Assets held for sale	0			0		0
Total assets	13,708			13,708		13,235
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	677		636	2,371	1,885
Segment net income (loss)	(65)		71	333	346
Goodwill	5,015			5,015		5,015
Assets held for sale	736			736		0
Total assets	23,235			23,235		22,630
Operating Segments | All Other
Segment Reporting Information [Line Items]
Operating revenues	154		135	288	248
Segment net income (loss)	(108)		(177)	(216)	(299)
Goodwill	263			263		263
Assets held for sale	49			49		55
Total assets	3,063			3,063		3,168
Operating Segments | All Other | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	11		8	18	16
Segment net income (loss)	(3)		(6)	1	(5)
Total assets	11,300			11,300		11,336
Operating Segments | Gas distribution operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	710		587	1,910	1,607
Segment net income (loss)	80		74	263	238
Total assets	20,245			20,245		19,090
Operating Segments | Gas Pipeline Investments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	8		8	16	16
Segment net income (loss)	(36)		21	(7)	51
Total assets	1,492			1,492		1,597
Operating Segments | Wholesale Gas Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	(110)		(19)	188	32
Segment net income (loss)	(112)		(23)	14	0
Total assets	807			807		850
Operating Segments | Gas marketing services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	64		56	259	233
Segment net income (loss)	6		5	62	62
Total assets	1,486			1,486		1,503
Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(40)		(35)	(75)	(74)
Segment net income (loss)	(2)		10	(9)	8
Goodwill	0			0		0
Assets held for sale	0			0		0
Total assets	(736)			(736)		(904)
Eliminations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	(6)		(4)	(20)	(19)
Segment net income (loss)	0		0	0	0
Total assets	(12,095)			(12,095)		(11,746)
Eliminations | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	(114)		(94)	(201)	(181)
Segment net income (loss)	0		$ 0	0	$ 0
Goodwill	0			0		0
Assets held for sale	0			0		0
Total assets	$ (693)			$ (693)		$ (680)