SEGMENT AND RELATED INFORMATION - Financial Data for Business Segments (Details) $ in Millions		3 Months Ended		6 Months Ended
	Jan. 17, 2020 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($) business_unit	Jun. 30, 2020 USD ($) business_unit	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Operating revenues		$ 4,620	$ 5,098	$ 9,638	$ 10,510
Segment net income (loss)		612	899	1,480	2,982
Goodwill		5,280		5,280		$ 5,280
Total assets		119,731		119,731		118,700
Leveraged lease investments impairment loss		154	0	154	0
Preliminary gain on sale				35	2,512
GEORGIA POWER CO
Segment Reporting Information [Line Items]
Operating revenues		1,928	2,117	3,754	3,951
Total assets		45,825		45,825		44,541
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues		439	510	814	953
Segment net income (loss)		63	174	138	230
Total assets		13,557		13,557		14,300
Preliminary gain on sale				39	23
SOUTHERN POWER CO | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Plant Mankato
Segment Reporting Information [Line Items]
Gain on sale				39
Gain on sale, net of tax				23
Preliminary gain on sale	$ 39
Preliminary gain on sale, net of tax	$ 23
SOUTHERN POWER CO | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Plant Nacogdoches
Segment Reporting Information [Line Items]
Preliminary gain on sale			23	23
Preliminary gain on sale, net of tax			88	88
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		636	689	1,885	2,163
Segment net income (loss)		71	106	346	376
Goodwill		5,015		5,015		5,015
Total assets		21,500		21,500		21,687
Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues		3,884	4,290	7,579	8,085
Segment net income (loss)		708	956	1,425	1,576
Goodwill		2		2		2
Total assets		96,002		96,002		94,650
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		636	689	1,885	2,163
All Other
Segment Reporting Information [Line Items]
Leveraged lease investments impairment loss		154		154
Leveraged lease investments impairment loss, net of tax		74		$ 74
All Other | Disposal Group, Disposed of by Sale, Not Discontinued Operations | GULF POWER CO
Segment Reporting Information [Line Items]
Preliminary pre-tax gain on sale			(15)		2,500
Preliminary after-tax gain on sale			(11)		1,300
Impairment charges			$ 32		32
Number of business units contemplated for sale | business_unit			1	1
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		(19)	$ 48	32	134
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		632	682	1,888	2,177
Segment net income (loss)		77	103	351	376
Total assets		22,010		22,010		22,228
Operating Segments | Traditional Electric Operating Companies | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues		3,539	3,899	6,946	7,343
Segment net income (loss)		645	782	1,287	1,346
Goodwill		0		0		0
Total assets		83,158		83,158		81,063
Operating Segments | SOUTHERN POWER CO | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues		439	510	814	953
Segment net income (loss)		63	174	138	230
Goodwill		2		2		2
Total assets		13,557		13,557		14,300
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		636	689	1,885	2,163
Segment net income (loss)		71	106	346	376
Goodwill		5,015		5,015		5,015
Total assets		21,500		21,500		21,687
Operating Segments | All Other
Segment Reporting Information [Line Items]
Operating revenues		135	186	248	368
Segment net income (loss)		(177)	(154)	(299)	1,041
Goodwill		263		263		263
Total assets		3,325		3,325		3,511
Operating Segments | All Other | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		8	13	16	24
Segment net income (loss)		(6)	3	(5)	0
Total assets		10,645		10,645		10,759
Operating Segments | Gas Distribution Operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		587	568	1,607	1,740
Segment net income (loss)		74	58	238	191
Total assets		18,276		18,276		18,204
Operating Segments | Gas Pipeline Investments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		8	8	16	16
Segment net income (loss)		21	25	51	57
Total assets		1,617		1,617		1,678
Operating Segments | Wholesale Gas Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		(19)	48	32	134
Segment net income (loss)		(23)	23	0	70
Total assets		637		637		850
Operating Segments | Gas Marketing Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		56	58	233	287
Segment net income (loss)		5	(3)	62	58
Total assets		1,480		1,480		1,496
Eliminations
Segment Reporting Information [Line Items]
Operating revenues		(35)	(67)	(74)	(106)
Segment net income (loss)		10	(9)	8	(11)
Goodwill		0		0		0
Total assets		(1,096)		(1,096)		(1,148)
Eliminations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		(4)	(6)	(19)	(38)
Segment net income (loss)		0	0	0	0
Total assets		(11,155)		(11,155)		(11,300)
Eliminations | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues		(94)	(119)	(181)	(211)
Segment net income (loss)		0	$ 0	0	$ 0
Goodwill		0		0		0
Total assets		(713)		(713)		$ (713)
Plant Vogtle Units 3 And 4 | GEORGIA POWER CO
Segment Reporting Information [Line Items]
Estimated loss on Plant Vogtle Units 3 and 4		149		149
Estimated loss on plants under construction, after tax		$ 111		$ 111