SEGMENT AND RELATED INFORMATION - Financial Data for Business Segments (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
	Jan. 17, 2020	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Operating revenues		$ 5,620		$ 5,995	$ 15,258	$ 16,505
Segment net income (loss)		1,251		1,316	2,732	4,298
Goodwill		5,280			5,280		$ 5,280
Total assets		123,158			123,158		118,700
Leveraged lease investments impairment loss		0	$ 154	0	154	0
Leveraged lease investments impairment loss, net of tax			$ 74
Impairment charges		0		110	0	142
Preliminary gain on sale					36	2,517
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues		523		574	1,337	1,527
Segment net income (loss)		74		86	212	316
Total assets		13,424			13,424		14,300
Preliminary gain on sale					39	24
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
Preliminary gain on sale, net of tax				88
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		477		498	2,362	2,661
Segment net income (loss)		14		(29)	360	347
Goodwill		5,015			5,015		5,015
Total assets		21,932			21,932		21,687
Impairment charges		0		92	0	92
Impairment charges, net of tax				65		65
GEORGIA POWER CO
Segment Reporting Information [Line Items]
Operating revenues		2,617		2,755	6,371	6,706
Total assets		47,046			47,046		44,541
Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues		5,049		5,363	12,628	13,448
Segment net income (loss)		1,358		1,459	2,783	3,035
Goodwill		2			2		2
Total assets		97,971			97,971		94,650
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		477		498	2,362	2,661
All Other
Segment Reporting Information [Line Items]
Leveraged lease investments impairment loss					154
Leveraged lease investments impairment loss, net of tax					74
All Other | Disposal Group, Disposed of by Sale, Not Discontinued Operations | GULF POWER CO
Segment Reporting Information [Line Items]
Impairment charges				18		50
Preliminary pre-tax gain on sale						2,500
Preliminary after-tax gain on sale						1,300
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		(51)		(2)	(19)	132
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		475		493	2,363	2,670
Segment net income (loss)		21		30	372	406
Total assets		22,435			22,435		22,228
Operating Segments | Traditional Electric Operating Companies | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues		4,629		4,908	11,576	12,252
Segment net income (loss)		1,284		1,373	2,571	2,719
Goodwill		0			0		0
Total assets		85,218			85,218		81,063
Operating Segments | SOUTHERN POWER CO | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues		523		574	1,337	1,527
Segment net income (loss)		74		86	212	316
Goodwill		2			2		2
Total assets		13,424			13,424		14,300
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		477		498	2,362	2,661
Segment net income (loss)		14		(29)	360	347
Goodwill		5,015			5,015		5,015
Total assets		21,932			21,932		21,687
Operating Segments | All Other
Segment Reporting Information [Line Items]
Operating revenues		132		146	380	514
Segment net income (loss)		(122)		(110)	(420)	931
Goodwill		263			263		263
Total assets		4,116			4,116		3,511
Operating Segments | All Other | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		8		10	24	34
Segment net income (loss)		(7)		(59)	(12)	(59)
Total assets		10,979			10,979		10,759
Operating Segments | Gas Distribution Operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		479		448	2,086	2,188
Segment net income (loss)		46		37	284	228
Total assets		18,715			18,715		18,204
Operating Segments | Gas Pipeline Investments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		8		8	24	24
Segment net income (loss)		23		6	74	63
Total assets		1,609			1,609		1,678
Operating Segments | Wholesale Gas Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		(51)		(2)	(19)	132
Segment net income (loss)		(45)		(9)	(45)	61
Total assets		650			650		850
Operating Segments | Gas Marketing Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		39		39	272	326
Segment net income (loss)		(3)		(4)	59	54
Total assets		1,461			1,461		1,496
Eliminations
Segment Reporting Information [Line Items]
Operating revenues		(38)		(12)	(112)	(118)
Segment net income (loss)		1		(4)	9	(15)
Goodwill		0			0		0
Total assets		(861)			(861)		(1,148)
Eliminations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		(6)		(5)	(25)	(43)
Segment net income (loss)		0		0	0	0
Total assets		(11,482)			(11,482)		(11,300)
Eliminations | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues		(103)		(119)	(285)	(331)
Segment net income (loss)		0		$ 0	0	$ 0
Goodwill		0			0		0
Total assets		(671)			(671)		$ (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