Derivatives - Balance Sheet Offsetting (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Southern Company [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	$ 45	$ 29
Derivatives presented in the Balance Sheet, liabilities	394	250
Southern Company [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets	2	1
Net interest rate derivative liabilities	191	214
Southern Company [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	12	7
Derivatives presented in the Balance Sheet, liabilities	201	220
Southern Company [Member] | Energy Related Derivative [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	(10)	(6)
Gross amounts not offset in the Balance Sheet, liabilities	(10)	(6)
Southern Company [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets	12	13
Net interest rate derivative liabilities	172	21
Southern Company [Member] | Interest Rate Contract [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	33	22
Derivatives presented in the Balance Sheet, liabilities	193	30
Southern Company [Member] | Interest Rate Contract [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	(21)	(9)
Gross amounts not offset in the Balance Sheet, liabilities	(21)	(9)
Alabama Power [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	3	1
Derivatives presented in the Balance Sheet, liabilities	49	70
Alabama Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets	0	0
Net interest rate derivative liabilities	46	54
Alabama Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	3	1
Derivatives presented in the Balance Sheet, liabilities	49	55
Alabama Power [Member] | Energy Related Derivative [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	(3)	(1)
Gross amounts not offset in the Balance Sheet, liabilities	(3)	(1)
Alabama Power [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets	0	0
Net interest rate derivative liabilities	0	15
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	0	15
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	18	7
Derivatives presented in the Balance Sheet, liabilities	11	21
Georgia Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets	1	0
Net interest rate derivative liabilities	8	13
Georgia Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	4	2
Derivatives presented in the Balance Sheet, liabilities	11	15
Georgia Power [Member] | Energy Related Derivative [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	(3)	(2)
Gross amounts not offset in the Balance Sheet, liabilities	(3)	(2)
Georgia Power [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets	14	1
Net interest rate derivative liabilities	0	2
Georgia Power [Member] | Interest Rate Contract [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	14	5
Derivatives presented in the Balance Sheet, liabilities	0	6
Georgia Power [Member] | Interest Rate Contract [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	0	(4)
Gross amounts not offset in the Balance Sheet, liabilities	0	(4)
Gulf Power [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	0	1
Derivatives presented in the Balance Sheet, liabilities	99	100
Gulf Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets	0	0
Net interest rate derivative liabilities	94	100
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	100
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	1
Net interest rate derivative liabilities	5	0
Gulf Power [Member] | Interest Rate Contract [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	0	1
Derivatives presented in the Balance Sheet, liabilities	5	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	44	47
Mississippi Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets	0	0
Net interest rate derivative liabilities	44	47
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	44	47
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	6	7
Derivatives presented in the Balance Sheet, liabilities	3	3
Southern Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets	3	3
Net interest rate derivative liabilities	1	2
Southern Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives presented in the Balance Sheet, assets	5	4
Derivatives presented in the Balance Sheet, liabilities	3	3
Southern Power [Member] | Energy Related Derivative [Member] | Gross Amount Of Derivatives [Member]
Derivative [Line Items]
Gross amounts not offset in the Balance Sheet, assets	(2)	(1)
Gross amounts not offset in the Balance Sheet, liabilities	(2)	(1)
Southern Power [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets	1	4
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	4
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