Segment and Related Information - Financial Data for Business Segments (Details) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($) utility	Mar. 31, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($) utility	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Operating revenues	$ 5,098		$ 5,627		$ 10,510	$ 11,999
Segment net income (loss)	899	$ 2,084	(154)	$ 938	2,982	784
Goodwill	5,282				5,282		$ 5,315
Total assets	114,867				114,867		116,914
Goodwill impairment	32				32
Asset impairment					32	161
Loss on disposition	(8)		36		(2,506)	36
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	689		730		2,163	2,369
Segment net income (loss)	106	270	(31)	279	376	248
Goodwill	5,015				5,015		5,015
Total assets	20,761				20,761		21,448
Goodwill impairment	0		0		0	42
Loss on disposition	0		$ 36		0	$ 36
SOUTHERN Co GAS | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Segment Reporting Information [Line Items]
Number of natural gas distribution utilities disposed | utility			3			3
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues	510		$ 555		953	$ 1,064
Segment net income (loss)	174	$ 56	22	$ 121	230	143
Total assets	14,518				14,518		14,883
Asset impairment	0		119		0	119
Impairment charge, net of tax			89			89
Loss on disposition	(23)		0		(23)	0
SOUTHERN POWER CO | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Plant Nacogdoches
Segment Reporting Information [Line Items]
Pre-tax gain on the sale of Plant Nacogdoches	23				23
Gain on the sale of Plant Nacogdoches, after tax	88				88
Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	4,290		4,565		8,085	8,948
Segment net income (loss)	956		(26)		1,576	706
Goodwill	2				2		2
Total assets	92,049				92,049		93,959
Traditional Electric Operating Companies | GEORGIA POWER AND MISSISSIPPI POWER CO | Kemper County Energy Facility
Segment Reporting Information [Line Items]
Public utilities, property, plant and equipment, amount of loss (recovery) on plant abandonment	4		1,100		6	1,100
Public utilities, property, plant and equipment, amount of loss (recovery) on plant abandonment after tax	3		800		5	800
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	689		730		2,163	2,369
SOUTHERN Co GAS | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Pivotal Home Solutions
Segment Reporting Information [Line Items]
Goodwill impairment						42
All Other | Disposal Group, Disposed of by Sale, Not Discontinued Operations | GULF POWER CO
Segment Reporting Information [Line Items]
Preliminary pre-tax gain (reduction)	15				2,500
Preliminary after-tax gain (reduction)	(11)				1,300
Gas Distribution Operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Goodwill	4,034				4,034		4,034
Gas Distribution Operations | SOUTHERN Co GAS | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Segment Reporting Information [Line Items]
Operating revenues			70			237
Gas Marketing Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Goodwill	981				981		981
Operating revenues			24			55
Loss on disposition			36			36
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	682		724		2,177	2,381
Segment net income (loss)	103		(8)		376	284
Total assets	21,360				21,360		21,918
Operating Segments | Traditional Electric Operating Companies | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	3,899		4,124		7,343	8,104
Segment net income (loss)	782		(48)		1,346	563
Goodwill	0				0		0
Total assets	78,314				78,314		79,382
Operating Segments | SOUTHERN POWER CO | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	510		555		953	1,064
Segment net income (loss)	174		22		230	143
Goodwill	2				2		2
Total assets	14,518				14,518		14,883
Operating Segments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	689		730		2,163	2,369
Segment net income (loss)	106		(31)		376	248
Goodwill	5,015				5,015		5,015
Total assets	20,761				20,761		21,448
Operating Segments | All Other
Segment Reporting Information [Line Items]
Operating revenues	186		381		368	782
Segment net income (loss)	(154)		(100)		1,041	(174)
Goodwill	265				265		298
Total assets	3,343				3,343		3,285
Operating Segments | All Other | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	13		11		24	26
Segment net income (loss)	3		(23)		0	(36)
Total assets	10,934				10,934		11,112
Operating Segments | Gas Distribution Operations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	568		643		1,740	1,856
Segment net income (loss)	58		68		191	216
Total assets	17,397				17,397		17,266
Operating Segments | Gas Pipeline Investments | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	8		8		16	16
Segment net income (loss)	25		21		57	48
Total assets	1,768				1,768		1,763
Operating Segments | Wholesale Gas Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	48		(16)		134	150
Segment net income (loss)	23		(21)		70	83
Total assets	668				668		1,302
Less Gross Gas Costs	1,238		1,454		3,165	3,393
Operating Segments | Wholesale Gas Services | SOUTHERN Co GAS | Third Party Gross Revenues
Segment Reporting Information [Line Items]
Operating revenues	1,223		1,336		3,148	3,274
Operating Segments | Wholesale Gas Services | SOUTHERN Co GAS | Intercompany Revenues
Segment Reporting Information [Line Items]
Operating revenues	63		102		151	269
Operating Segments | Wholesale Gas Services | SOUTHERN Co GAS | Total Gross Revenues
Segment Reporting Information [Line Items]
Operating revenues	1,286		1,438		3,299	3,543
Operating Segments | Gas Marketing Services | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	58		89		287	359
Segment net income (loss)	(3)		(76)		58	(63)
Total assets	1,527				1,527		1,587
Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(67)		(49)		(106)	(100)
Segment net income (loss)	(9)		3		(11)	4
Goodwill	0				0		0
Total assets	(1,286)				(1,286)		(1,778)
Eliminations | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	(6)		(5)		(38)	(38)
Segment net income (loss)	0		0		0	0
Total assets	(11,533)				(11,533)		(11,582)
Eliminations | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	(119)		(114)		(211)	(220)
Segment net income (loss)	0		$ 0		0	$ 0
Goodwill	0				0		0
Total assets	$ (783)				$ (783)		$ (306)