Derivatives - Balance Sheet Presentation (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	$ 1
Southern Company [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	24	$ 21
Derivatives, liabilities	247	225
Southern Company [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets		6
Southern Company [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		4
Southern Company [Member] | Hedging Instruments for Regulatory Purposes [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	4	7
Derivatives, liabilities	211	197
Southern Company [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	7
Southern Company [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	0
Southern Company [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	117	118
Southern Company [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	94	79
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	19	8
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		24
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	11	7
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	8	1
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	36	17
Southern Company [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		7
Alabama Power [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	1
Derivatives, liabilities	71	61
Alabama Power [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets		0
Alabama Power [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		0
Alabama Power [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0
Alabama Power [Member] | Hedging Instruments for Regulatory Purposes [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	1
Derivatives, liabilities	54	53
Alabama Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	1
Alabama Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	0
Alabama Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	36	32
Alabama Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	18	21
Alabama Power [Member] | Cash Flow and Fair Value Hedging [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Alabama Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		8
Alabama Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Alabama Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Alabama Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	17	8
Alabama Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		0
Georgia Power [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	11	13
Derivatives, liabilities	35	41
Georgia Power [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets		0
Georgia Power [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		0
Georgia Power [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0
Georgia Power [Member] | Hedging Instruments for Regulatory Purposes [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	7
Derivatives, liabilities	16	27
Georgia Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	6
Georgia Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Georgia Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	14	23
Georgia Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	2	4
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	9	6
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		14
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	5	5
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	4	1
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	19	9
Georgia Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		5
Gulf Power [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Derivatives, liabilities	94	72
Gulf Power [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets		0
Gulf Power [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		0
Gulf Power [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Derivatives, liabilities	94	72
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	41	37
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	53	35
Gulf Power [Member] | Cash Flow and Fair Value Hedging [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Gulf Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		0
Gulf Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Gulf Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Gulf Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
Gulf Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		0
Mississippi Power [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Derivatives, liabilities	47	45
Mississippi Power [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets		0
Mississippi Power [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		0
Mississippi Power [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Derivatives, liabilities	47	45
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	26	26
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	21	19
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		0
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
Mississippi Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		0
Southern Power [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	5
Derivatives, liabilities	0	4
Southern Power [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets		5
Southern Power [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		4
Southern Power [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other deferred charges and assets [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	1
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member]
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		0
Southern Power [Member] | Cash Flow and Fair Value Hedging [Member] | Interest Rate 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] | Interest Rate 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] | 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] | Interest Rate Contract [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivatives, liabilities		$ 0