Derivatives - Balance Sheet Offsetting (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Southern Company [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	$ 24	$ 21
Derivatives presented in the Balance Sheet, liabilities	247	225
Southern Company [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets	0	4
Net interest rate derivative liabilities	207	192
Southern Company [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	4	13
Derivatives presented in the Balance Sheet, liabilities	211	201
Southern Company [Member] | Energy Related Derivative [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	(4)	(9)
Gross amounts not offset in the Balance Sheet, liabilities	(4)	(9)
Southern Company [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets	11	0
Net interest rate derivative liabilities	27	16
Southern Company [Member] | Interest Rate Contract [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	20	8
Derivatives presented in the Balance Sheet, liabilities	36	24
Southern Company [Member] | Interest Rate Contract [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	(9)	(8)
Gross amounts not offset in the Balance Sheet, liabilities	(9)	(8)
Alabama Power [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	2	1
Derivatives presented in the Balance Sheet, liabilities	71	61
Alabama Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets	0	1
Net interest rate derivative liabilities	52	53
Alabama Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	2	1
Derivatives presented in the Balance Sheet, liabilities	54	53
Alabama Power [Member] | Energy Related Derivative [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	(2)	0
Gross amounts not offset in the Balance Sheet, liabilities	(2)	0
Alabama Power [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets	0	0
Net interest rate derivative liabilities	17	8
Alabama Power [Member] | Interest Rate Contract [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	0	0
Derivatives presented in the Balance Sheet, liabilities	17	8
Alabama Power [Member] | Interest Rate Contract [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	0	0
Gross amounts not offset in the Balance Sheet, liabilities	0	0
Georgia Power [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	11	13
Derivatives presented in the Balance Sheet, liabilities	35	41
Georgia Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets	0	0
Net interest rate derivative liabilities	14	20
Georgia Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	2	7
Derivatives presented in the Balance Sheet, liabilities	16	27
Georgia Power [Member] | Energy Related Derivative [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	(2)	(7)
Gross amounts not offset in the Balance Sheet, liabilities	(2)	(7)
Georgia Power [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets	7	0
Net interest rate derivative liabilities	17	8
Georgia Power [Member] | Interest Rate Contract [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	9	6
Derivatives presented in the Balance Sheet, liabilities	19	14
Georgia Power [Member] | Interest Rate Contract [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	(2)	(6)
Gross amounts not offset in the Balance Sheet, liabilities	(2)	(6)
Gulf Power [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	0	0
Derivatives presented in the Balance Sheet, liabilities	94	72
Gulf Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets	0	0
Net interest rate derivative liabilities	94	72
Gulf Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	0	0
Derivatives presented in the Balance Sheet, liabilities	94	72
Gulf Power [Member] | Energy Related Derivative [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	0	0
Gross amounts not offset in the Balance Sheet, liabilities	0	0
Gulf Power [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets	0	0
Net interest rate derivative liabilities	0	0
Gulf Power [Member] | Interest Rate Contract [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	0	0
Derivatives presented in the Balance Sheet, liabilities	0	0
Gulf Power [Member] | Interest Rate Contract [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	0	0
Gross amounts not offset in the Balance Sheet, liabilities	0	0
Mississippi Power [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	0	0
Derivatives presented in the Balance Sheet, liabilities	47	45
Mississippi Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets	0	0
Net interest rate derivative liabilities	47	45
Mississippi Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	0	0
Derivatives presented in the Balance Sheet, liabilities	47	45
Mississippi Power [Member] | Energy Related Derivative [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	0	0
Gross amounts not offset in the Balance Sheet, liabilities	0	0
Mississippi Power [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets	0	0
Net interest rate derivative liabilities	0	0
Mississippi Power [Member] | Interest Rate Contract [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	0	0
Derivatives presented in the Balance Sheet, liabilities	0	0
Mississippi Power [Member] | Interest Rate Contract [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	0	0
Gross amounts not offset in the Balance Sheet, liabilities	0	0
Southern Power [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	1	5
Derivatives presented in the Balance Sheet, liabilities	0	4
Southern Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets	0	5
Net interest rate derivative liabilities	0	4
Southern Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	0	5
Derivatives presented in the Balance Sheet, liabilities	0	4
Southern Power [Member] | Energy Related Derivative [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	0	0
Gross amounts not offset in the Balance Sheet, liabilities	0	0
Southern Power [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets	1	0
Net interest rate derivative liabilities	0	0
Southern Power [Member] | Interest Rate Contract [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	1	0
Derivatives presented in the Balance Sheet, liabilities	0	0
Southern Power [Member] | Interest Rate Contract [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	0	0
Gross amounts not offset in the Balance Sheet, liabilities	$ 0	$ 0