Derivatives - Balance Sheet Offsetting (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Southern Company [Member]
Derivative [Line Items]
Derivatives, assets	$ 442	$ 29
Derivatives, liabilities	572	250
Southern Company [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets		1
Net interest rate derivative liabilities		214
Southern Company [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives, assets		7
Derivatives, liabilities		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		(6)
Gross amounts not offset in the Balance Sheet, liabilities		(6)
Southern Company [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets		13
Net interest rate derivative liabilities		21
Southern Company [Member] | Interest Rate Contract [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives, assets		22
Derivatives, liabilities		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		(9)
Gross amounts not offset in the Balance Sheet, liabilities		(9)
Alabama Power [Member]
Derivative [Line Items]
Derivatives, assets	8	1
Derivatives, liabilities	21	70
Alabama Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets		0
Net interest rate derivative liabilities		54
Alabama Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives, assets		1
Derivatives, liabilities		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		(1)
Gross amounts not offset in the Balance Sheet, liabilities		(1)
Alabama Power [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets		0
Net interest rate derivative liabilities		15
Alabama Power [Member] | Interest Rate Contract [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives, assets		0
Derivatives, liabilities		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
Gross amounts not offset in the Balance Sheet, liabilities		0
Georgia Power [Member]
Derivative [Line Items]
Derivatives, assets	25	7
Derivatives, liabilities	16	21
Georgia Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets		0
Net interest rate derivative liabilities		13
Georgia Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives, assets		2
Derivatives, liabilities		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		(2)
Gross amounts not offset in the Balance Sheet, liabilities		(2)
Georgia Power [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets		1
Net interest rate derivative liabilities		2
Georgia Power [Member] | Interest Rate Contract [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives, assets		5
Derivatives, liabilities		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		(4)
Gross amounts not offset in the Balance Sheet, liabilities		(4)
Gulf Power [Member]
Derivative [Line Items]
Derivatives, assets	1	1
Derivatives, liabilities	57	100
Gulf Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets		0
Net interest rate derivative liabilities		100
Gulf Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives, assets		0
Derivatives, liabilities		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
Gross amounts not offset in the Balance Sheet, liabilities		0
Gulf Power [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets		1
Net interest rate derivative liabilities		0
Gulf Power [Member] | Interest Rate Contract [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives, assets		1
Derivatives, liabilities		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
Gross amounts not offset in the Balance Sheet, liabilities		0
Mississippi Power [Member]
Derivative [Line Items]
Derivatives, assets	1
Derivatives, liabilities	22	47
Mississippi Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets		0
Net interest rate derivative liabilities		47
Mississippi Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives, assets		0
Derivatives, liabilities		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
Gross amounts not offset in the Balance Sheet, liabilities		0
Mississippi Power [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets		0
Net interest rate derivative liabilities		0
Mississippi Power [Member] | Interest Rate Contract [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives, assets		0
Derivatives, liabilities		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
Gross amounts not offset in the Balance Sheet, liabilities		0
Southern Power [Member]
Derivative [Line Items]
Derivatives, assets	26	7
Derivatives, liabilities	$ 27	3
Southern Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Net derivative assets		3
Net interest rate derivative liabilities		2
Southern Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives, assets		4
Derivatives, liabilities		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		(1)
Gross amounts not offset in the Balance Sheet, liabilities		(1)
Southern Power [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Net derivative assets		3
Net interest rate derivative liabilities		0
Southern Power [Member] | Interest Rate Contract [Member] | Net Amount Of Derivatives [Member]
Derivative [Line Items]
Derivatives, assets		3
Derivatives, liabilities		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
Gross amounts not offset in the Balance Sheet, liabilities		$ 0