Derivatives - Derivative Financial Statement Presentation and Amounts With Balance Sheet Offsetting (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Collateral already posted, aggregate fair value	$ 71
Southern Company
Derivatives, Fair Value [Line Items]
Derivatives, assets	450	$ 690
Derivatives, liabilities	410	718
Derivative asset amount offset	(219)	(462)
Derivative liability amount offset	(290)	(524)
Derivative asset	231	228
Derivative liability	120	194
Southern Company | Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivatives, assets	339	556
Derivatives, liabilities	288	564
Southern Company | Derivatives not designated as hedging instruments | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	237	489
Southern Company | Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	102	66
Southern Company | Derivatives not designated as hedging instruments | Energy-related derivatives | Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	202	483
Southern Company | Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	86	81
Southern Company | Derivatives not designated as hedging instruments | Interest rate derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Southern Company | Derivatives not designated as hedging instruments | Interest rate derivatives | Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Derivatives, assets	31	98
Derivatives, liabilities	66	60
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	23	73
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	8	25
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	35	27
Southern Company | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	31	33
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivatives, assets	80	36
Derivatives, liabilities	56	94
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	13	23
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Energy-related derivatives | Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	10	7
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Interest rate derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	11	12
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Interest rate derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Interest rate derivatives | Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	1	1
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Interest rate derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	22	28
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Foreign currency derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Foreign currency derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	56	0
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Foreign currency derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	33
Southern Company | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Foreign currency derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	23	25
ALABAMA POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	9	20
Derivatives, liabilities	11	9
Derivative asset amount offset	(6)	(8)
Derivative liability amount offset	(6)	(8)
Derivative asset	3	12
Derivative liability	5	1
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivatives, assets	9	20
Derivatives, liabilities	11	9
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	7	13
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	7
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	7	5
ALABAMA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	4	4
GEORGIA POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	16	46
Derivatives, liabilities	17	11
Derivative asset amount offset	(9)	(8)
Derivative liability amount offset	(9)	(8)
Derivative asset	7	38
Derivative liability	8	3
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivatives, assets	15	44
Derivatives, liabilities	14	8
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	10	30
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	5	14
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	10	7
GEORGIA POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	4	1
GEORGIA POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	2
Derivatives, liabilities	3	3
GEORGIA POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Interest rate derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	2
GEORGIA POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Interest rate derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
GEORGIA POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Interest rate derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	2	3
GEORGIA POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Interest rate derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	1	0
GULF POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	5
Derivatives, liabilities	29	29
Derivative asset amount offset	(1)	(4)
Derivative liability amount offset	(1)	(4)
Derivative asset	0	1
Derivative liability	28	25
GULF POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	5
Derivatives, liabilities	29	29
GULF POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	4
GULF POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
GULF POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	16	12
GULF POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	13	17
MISSISSIPPI POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	5	7
Derivatives, liabilities	10	11
Derivative asset amount offset	(2)	(3)
Derivative liability amount offset	(2)	(3)
Derivative asset	3	4
Derivative liability	8	8
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivatives, assets	2	4
Derivatives, liabilities	10	11
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	2
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	2
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	4	5
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	6	6
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	3
Derivatives, liabilities	0	0
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Interest rate derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	3	2
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Interest rate derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Interest rate derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
MISSISSIPPI POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Interest rate derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
SOUTHERN POWER CO
Derivatives, Fair Value [Line Items]
Derivatives, assets	70	22
Derivatives, liabilities	32	63
Derivative asset amount offset	(2)	(5)
Derivative liability amount offset	(2)	(5)
Derivative asset	68	17
Derivative liability	30	58
SOUTHERN POWER CO | Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	4
Derivatives, liabilities	1	1
SOUTHERN POWER CO | Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	1	3
SOUTHERN POWER CO | Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	1	1
SOUTHERN POWER CO | Derivatives not designated as hedging instruments | Interest rate derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
SOUTHERN POWER CO | Derivatives not designated as hedging instruments | Interest rate derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivatives, assets	69	18
Derivatives, liabilities	31	62
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Energy-related derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	13	18
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Energy-related derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	8	4
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Foreign currency derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	0
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Foreign currency derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	56	0
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Foreign currency derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	33
SOUTHERN POWER CO | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Foreign currency derivatives | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	23	25
SOUTHERN Co GAS
Derivatives, Fair Value [Line Items]
Derivatives, assets	342	581
Derivatives, liabilities	291	569
Derivative asset amount offset	(196)	(435)
Derivative liability amount offset	(267)	(497)
Derivative asset	146	146
Derivative liability	24	72
Collateral already posted, aggregate fair value	71	62
SOUTHERN Co GAS | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Collateral already posted, aggregate fair value	1	8
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Derivatives, assets	338	552
Derivatives, liabilities	287	563
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	102	66
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	86	81
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Energy-related derivatives | Assets From Risk Management Activities
Derivatives, Fair Value [Line Items]
Derivatives, assets	236	486
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Energy-related derivatives | Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	201	482
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives
Derivatives, Fair Value [Line Items]
Derivatives, assets	4	25
Derivatives, liabilities	2	3
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other deferred charges and assets
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	1
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Other deferred credits and liabilities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	0	0
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Assets From Risk Management Activities
Derivatives, Fair Value [Line Items]
Derivatives, assets	4	24
SOUTHERN Co GAS | Derivatives designated as hedging instruments for regulatory purposes | Designated as Hedging Instrument | Energy-related derivatives | Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	2	3
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Energy-related derivatives | Assets From Risk Management Activities
Derivatives, Fair Value [Line Items]
Derivatives, assets	0	4
SOUTHERN Co GAS | Derivatives designated as hedging instruments in cash flow and fair value hedges | Designated as Hedging Instrument | Energy-related derivatives | Liabilities from risk management activities
Derivatives, Fair Value [Line Items]
Derivatives, liabilities	$ 2	$ 3