REVENUE FROM CONTRACTS WITH CUSTOMERS - Disaggregate Revenue Sources (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 23,463	$ 21,097	$ 22,596
Total operating revenues	23,113	20,375	21,419
Retail electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14,244	13,677	14,445
Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6,207	6,113	6,164
Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4,877	4,699	5,065
Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,067	2,775	3,126
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	93	90	90
Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,625	2,888	2,989
Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,799	1,338	1,413
Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	470	340	389
Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,038	971	907
Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	49	30	35
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	269	209	245
Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,851	1,399	1,518
PPA energy revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,122	735	833
PPA capacity revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	493	454	453
Non-PPA revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	236	210	232
Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,668	2,151	2,609
Gas pipeline investments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers			32
Wholesale gas services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,168	1,727	2,095
Gas marketing services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	464	391	440
Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	36	33	42
Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,075	982	1,035
Other revenue sources
Disaggregation of Revenue [Line Items]
Other	3,349	3,764	4,266
Other adjustments
Disaggregation of Revenue [Line Items]
Other	(3,699)	(4,486)	(5,443)
Alabama Power
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6,141	5,646	6,152
Total operating revenues	6,413	5,830	6,125
Alabama Power | Retail electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5,470	5,203	5,671
Alabama Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,467	2,377	2,509
Alabama Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,600	1,512	1,677
Alabama Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,386	1,293	1,460
Alabama Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	17	21	25
Alabama Power | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	469	284	328
Alabama Power | PPA energy revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	184	133	145
Alabama Power | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	115	108	102
Alabama Power | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	170	43	81
Alabama Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers			0
Alabama Power | Wholesale gas services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Gas marketing services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Alabama Power | Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	202	159	153
Alabama Power | Other revenue sources
Disaggregation of Revenue [Line Items]
Other	272	184	(27)
Alabama Power | Other adjustments
Disaggregation of Revenue [Line Items]
Other	0	0	0
Georgia Power
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8,563	8,215	8,418
Total operating revenues	9,260	8,309	8,408
Georgia Power | Retail electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7,940	7,666	7,888
Georgia Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,471	3,476	3,377
Georgia Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,010	2,933	3,097
Georgia Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,391	1,197	1,360
Georgia Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	68	60	54
Georgia Power | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	171	102	123
Georgia Power | PPA energy revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	95	42	60
Georgia Power | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	55	50	54
Georgia Power | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	21	10	9
Georgia Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers			0
Georgia Power | Wholesale gas services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Gas marketing services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Georgia Power | Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	452	447	407
Georgia Power | Other revenue sources
Disaggregation of Revenue [Line Items]
Other	697	94	(10)
Georgia Power | Other adjustments
Disaggregation of Revenue [Line Items]
Other	0	0	0
Mississippi Power
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,282	1,157	1,271
Total operating revenues	1,322	1,172	1,264
Mississippi Power | Retail electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	834	808	886
Mississippi Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	269	260	278
Mississippi Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	267	254	291
Mississippi Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	290	285	306
Mississippi Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8	9	11
Mississippi Power | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	417	323	366
Mississippi Power | PPA energy revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11	9	11
Mississippi Power | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5	3	3
Mississippi Power | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	401	311	352
Mississippi Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers			0
Mississippi Power | Wholesale gas services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Gas marketing services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Mississippi Power | Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	31	26	19
Mississippi Power | Other revenue sources
Disaggregation of Revenue [Line Items]
Other	40	15	(7)
Mississippi Power | Other adjustments
Disaggregation of Revenue [Line Items]
Other	0	0	0
Southern Power
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,605	1,119	1,220
Total operating revenues	2,216	1,733	1,938
Southern Power | Retail electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,575	1,105	1,208
Southern Power | PPA energy revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	854	570	648
Southern Power | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	323	296	322
Southern Power | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	398	239	238
Southern Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers			0
Southern Power | Wholesale gas services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Gas marketing services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Power | Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	30	14	12
Southern Power | Other revenue sources
Disaggregation of Revenue [Line Items]
Other	611	614	718
Southern Power | Other adjustments
Disaggregation of Revenue [Line Items]
Other	0	0	0
Southern Company Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6,293	5,039	5,598
Total operating revenues	4,380	3,434	3,792
Southern Company Gas | Retail electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,625	2,888	2,989
Southern Company Gas | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,799	1,338	1,413
Southern Company Gas | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	470	340	389
Southern Company Gas | Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,038	971	907
Southern Company Gas | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	49	30	35
Southern Company Gas | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	269	209	245
Southern Company Gas | Wholesale electric revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | PPA energy revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,668	2,151	2,609
Southern Company Gas | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers			32
Southern Company Gas | Wholesale gas services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,168	1,727	2,095
Southern Company Gas | Gas marketing services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	464	391	440
Southern Company Gas | Other natural gas revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	36	33	42
Southern Company Gas | Other revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Southern Company Gas | Other revenue sources
Disaggregation of Revenue [Line Items]
Other	1,786	2,881	3,637
Southern Company Gas | Other adjustments
Disaggregation of Revenue [Line Items]
Other	$ (3,699)	$ (4,486)	$ (5,443)