Segment and Related Information - Schedule of Financial Data for Business Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Operating revenues	$ 5,910	$ 5,018
Segment net income (loss)	1,135	868
Goodwill	5,280		$ 5,280
Total assets	125,393		122,935
Estimated loss on Plant Vogtle Units 3 and 4	48	0
Gain on sale	41	38
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues	440	375
Segment net income (loss)	97	75
Total assets	13,995		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	1,694	1,249
Segment net income (loss)	398	275
Goodwill	5,015		5,015
Total assets	23,377		22,630
GEORGIA POWER CO
Segment Reporting Information [Line Items]
Operating revenues	1,970	1,825
Total assets	47,349		47,080
Estimated loss on Plant Vogtle Units 3 and 4	48	0
Estimated loss on Plant Vogtle Units 3 and 4, net of tax	36
Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	4,117	3,695
Segment net income (loss)	853	717
Goodwill	2		2
Total assets	99,411		98,041
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	1,694	1,249
Gas distribution operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Goodwill	4,034		4,034
Wholesale Gas Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	298	51
Gas marketing services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Goodwill	981		981
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	1,701	1,256
Segment net income (loss)	394	274
Total assets	24,249		23,040
Operating Segments | Traditional Electric Operating Companies | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	3,764	3,407
Segment net income (loss)	756	642
Goodwill	0		0
Total assets	86,053		85,486
Operating Segments | SOUTHERN POWER CO | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	440	375
Segment net income (loss)	97	75
Goodwill	2		2
Total assets	13,995		13,235
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	1,694	1,249
Segment net income (loss)	398	275
Goodwill	5,015		5,015
Total assets	23,377		22,630
Operating Segments | All Other
Segment Reporting Information [Line Items]
Operating revenues	134	114
Segment net income (loss)	(108)	(121)
Goodwill	263		263
Total assets	3,392		3,168
Operating Segments | All Other | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	7	8
Segment net income (loss)	4	1
Total assets	11,477		11,336
Operating Segments | Gas distribution operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	1,200	1,020
Segment net income (loss)	183	164
Total assets	20,161		19,090
Operating Segments | Gas Pipeline Investments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	8	8
Segment net income (loss)	29	30
Total assets	1,596		1,597
Operating Segments | Wholesale Gas Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	298	51
Segment net income (loss)	126	23
Total assets	939		850
Operating Segments | Gas marketing services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	195	177
Segment net income (loss)	56	57
Total assets	1,553		1,503
Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(35)	(40)
Segment net income (loss)	(8)	(3)
Goodwill	0		0
Total assets	(787)		(904)
Eliminations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	(14)	(15)
Segment net income (loss)	0	0
Total assets	(12,349)		(11,746)
Eliminations | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	(87)	(87)
Segment net income (loss)	0	$ 0
Goodwill	0		0
Total assets	$ (637)		$ (680)