Revenue from Contracts with Customers - Disaggregate Revenue Sources (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 5,412	$ 6,372
Revenue from leases	139
Total retail electric and gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	4,245	4,768
Retail electric revenues
Disaggregation of Revenue [Line Items]
Revenue from leases	8	18
Increase (decrease) in revenue from cost recovery mechanisms	(103)	117
Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	1,288	1,539
Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	1,093	1,243
Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	677	756
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	26	30
Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,163	1,224
Alternative revenue programs
Disaggregation of Revenue [Line Items]
Total operating revenues	(2)	(24)
Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	367	472
Revenue from leases	66	69
Revenue from transactions accounted for as derivatives	53	93
Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	132	151
Revenue from leases	25	30
Other natural gas revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	313	407
Revenue from leases	9
Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	355	574
Revenue from leases	31	33
Revenues not accounted for under ASC 606	96	90
ALABAMA POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	1,408	1,473
ALABAMA POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,213	1,285
Increase (decrease) in revenue from cost recovery mechanisms	(57)	47
ALABAMA POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	540	570
ALABAMA POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	354	371
ALABAMA POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	313	338
ALABAMA POWER CO | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	6	6
ALABAMA POWER CO | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	94	101
Revenue from transactions accounted for as derivatives	3	5
ALABAMA POWER CO | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	27	24
ALABAMA POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	74	63
Revenues not accounted for under ASC 606	28	25
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	1,833	1,961
Revenue from leases	19
GEORGIA POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,668	1,798
Revenue from leases	8	18
Increase (decrease) in revenue from cost recovery mechanisms	(47)	10
GEORGIA POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	688	744
GEORGIA POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	674	717
GEORGIA POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	289	316
GEORGIA POWER CO | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	17	21
GEORGIA POWER CO | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	18	40
Revenue from transactions accounted for as derivatives	4	7
GEORGIA POWER CO | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	14	14
GEORGIA POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	133	109
Revenue from leases	11	33
Revenues not accounted for under ASC 606	31	26
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	287	302
Revenue from leases	2
MISSISSIPPI POWER CO | Retail electric revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	203	194
Increase (decrease) in revenue from cost recovery mechanisms	1	76
MISSISSIPPI POWER CO | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	60	60
MISSISSIPPI POWER CO | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	65	62
MISSISSIPPI POWER CO | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	74	70
MISSISSIPPI POWER CO | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	4	2
MISSISSIPPI POWER CO | Wholesale energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	78	98
Revenue from transactions accounted for as derivatives	1	1
MISSISSIPPI POWER CO | Wholesale capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1	4
MISSISSIPPI POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	5	6
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Total operating revenues	443	509
Revenue from leases	113
SOUTHERN POWER CO | PPA capacity revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	127	138
Revenue from leases	41	47
SOUTHERN POWER CO | PPA energy revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	227	254
Revenue from leases	72	76
SOUTHERN POWER CO | Non-PPA revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	85	115
Revenue from transactions accounted for as derivatives	45	79
SOUTHERN POWER CO | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	4	2
SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Total operating revenues	1,474	1,639
Revenue from leases	9
SOUTHERN Co GAS | Wholesale Gas Services | Third Party Gross Revenues
Disaggregation of Revenue [Line Items]
Revenue from transactions accounted for as derivatives	1,200	1,100
SOUTHERN Co GAS | Natural gas distribution revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1,161	1,200
SOUTHERN Co GAS | Residential
Disaggregation of Revenue [Line Items]
Total operating revenues	601	660
SOUTHERN Co GAS | Commercial
Disaggregation of Revenue [Line Items]
Total operating revenues	170	192
SOUTHERN Co GAS | Transportation
Disaggregation of Revenue [Line Items]
Total operating revenues	256	277
SOUTHERN Co GAS | Industrial
Disaggregation of Revenue [Line Items]
Total operating revenues	17	17
SOUTHERN Co GAS | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	119	78
SOUTHERN Co GAS | Alternative revenue programs
Disaggregation of Revenue [Line Items]
Total operating revenues	(2)	(24)
SOUTHERN Co GAS | Gas pipeline investments
Disaggregation of Revenue [Line Items]
Total operating revenues	8	8
Revenue from leases	8
SOUTHERN Co GAS | Wholesale Gas Services
Disaggregation of Revenue [Line Items]
Total operating revenues	66	146
SOUTHERN Co GAS | Gas marketing services
Disaggregation of Revenue [Line Items]
Total operating revenues	229	271
Revenues not accounted for under ASC 606	6	4
SOUTHERN Co GAS | Other revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	10	14
Operating Segments | SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Total operating revenues	1,495	1,657
Operating Segments | SOUTHERN Co GAS | Wholesale Gas Services
Disaggregation of Revenue [Line Items]
Total operating revenues	86	166
Operating Segments | SOUTHERN Co GAS | Wholesale Gas Services | Third Party Gross Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 1,926	$ 1,938