Derivatives - Derivative Financial Statement Presentation and Amounts With Balance Sheet Offsetting (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Collateral already posted, aggregate fair value	$ 92
Southern Company [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	519	$ 690
Derivatives, liabilities	552	718
Derivative asset amount offset	(303)	(462)
Derivative liability amount offset	(395)	(524)
Derivative asset	216	228
Derivative liability	157	194
Southern Company [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	438	556
Derivatives, liabilities	385	564
Southern Company [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	306	489
Southern Company [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	132	66
Southern Company [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	271	483
Southern Company [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	114	81
Southern Company [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Southern Company [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
Southern Company [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	54	98
Derivatives, liabilities	68	60
Southern Company [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	48	73
Southern Company [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	6	25
Southern Company [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	30	27
Southern Company [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	38	33
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	27	36
Derivatives, liabilities	99	94
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	14	23
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	5	7
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	13	12
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	1
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	32	28
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	37	33
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	25	25
Alabama Power [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	11	20
Derivatives, liabilities	10	9
Derivative asset amount offset	(6)	(8)
Derivative liability amount offset	(6)	(8)
Derivative asset	5	12
Derivative liability	4	1
Alabama Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	11	20
Derivatives, liabilities	10	9
Alabama Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	9	13
Alabama Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	7
Alabama Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	5	5
Alabama Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	5	4
Georgia Power [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	26	46
Derivatives, liabilities	17	11
Derivative asset amount offset	(6)	(8)
Derivative liability amount offset	(6)	(8)
Derivative asset	20	38
Derivative liability	11	3
Georgia Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	24	44
Derivatives, liabilities	13	8
Georgia Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	20	30
Georgia Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	4	14
Georgia Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	11	7
Georgia Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	2	1
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	2
Derivatives, liabilities	4	3
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	2
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	4	3
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
Gulf Power [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	5
Derivatives, liabilities	31	29
Derivative asset amount offset	(2)	(4)
Derivative liability amount offset	(2)	(4)
Derivative asset	0	1
Derivative liability	29	25
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	5
Derivatives, liabilities	31	29
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	4
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	14	12
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	17	17
Mississippi Power [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	7	7
Derivatives, liabilities	12	11
Derivative asset amount offset	(2)	(3)
Derivative liability amount offset	(2)	(3)
Derivative asset	5	4
Derivative liability	10	8
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	4
Derivatives, liabilities	12	11
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	2
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	2
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	5	5
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	7	6
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	4	3
Derivatives, liabilities	0	0
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	4	2
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
Southern Power [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	15	22
Derivatives, liabilities	67	63
Derivative asset amount offset	(3)	(5)
Derivative liability amount offset	(3)	(5)
Derivative asset	12	17
Derivative liability	64	58
Southern Power [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	4
Derivatives, liabilities	1	1
Southern Power [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	3
Southern Power [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	1	1
Southern Power [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Southern Power [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	13	18
Derivatives, liabilities	66	62
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	13	18
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	4	4
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	37	33
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	25	25
Southern Company Gas [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	451	581
Derivatives, liabilities	387	569
Derivative asset amount offset	(272)	(435)
Derivative liability amount offset	(364)	(497)
Derivative asset	179	146
Derivative liability	23	72
Collateral already posted, aggregate fair value	92	62
Southern Company Gas [Member] | Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Collateral already posted, aggregate fair value	4	8
Southern Company Gas [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	436	552
Derivatives, liabilities	384	563
Southern Company Gas [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	132	66
Southern Company Gas [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	114	81
Southern Company Gas [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Assets From Risk Management Activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	304	486
Southern Company Gas [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	270	482
Southern Company Gas [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	14	25
Derivatives, liabilities	2	3
Southern Company Gas [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Southern Company Gas [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
Southern Company Gas [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Assets From Risk Management Activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	14	24
Southern Company Gas [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	2	3
Southern Company Gas [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Assets From Risk Management Activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	4
Southern Company Gas [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	$ 1	$ 3