Derivatives - Textual (Details)		1 Months Ended		3 Months Ended	6 Months Ended	12 Months Ended
	Jan. 23, 2015 USD ($)	Sep. 30, 2016 USD ($)	May 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) MMBTU	Dec. 31, 2016 USD ($) MMBTU	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Nov. 30, 2015 USD ($)
Derivative [Line Items]
Notional Amount					$ 4,027,000,000	$ 4,027,000,000
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU						9,000,000
Realized gain (loss) on termination of interest rate derivatives						$ (220,000,000)	$ (22,000,000)	$ (16,000,000)
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period					(21,000,000)	(21,000,000)
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months						17,000,000
Gulf Power [Member]
Derivative [Line Items]
Derivative collateral obligation to return cash					$ 0	$ 0
Net volume of energy-related derivative contracts for natural gas positions | MMBTU					51,000,000	51,000,000
Longest Hedge Date						2020
Mississippi Power [Member]
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU					36,000,000	36,000,000
Longest Hedge Date						2020
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period					$ (2,000,000)	$ (2,000,000)
Georgia Power [Member]
Derivative [Line Items]
Required Period For Options And Hedges						48 months	24 months
Notional Amount					950,000,000	$ 950,000,000
Derivative collateral obligation to return cash					0	$ 0
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU						3,000,000
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period					4,000,000	$ 4,000,000
Southern Company Gas [Member]
Derivative [Line Items]
Fair value of derivative liabilities with contingent features					5,000,000	5,000,000
Maximum potential collateral requirements arising the from credit-risk-related contingent features					9,000,000	9,000,000
Alabama Power [Member]
Derivative [Line Items]
Derivative collateral obligation to return cash					0	$ 0
Longest Hedge Date						2020
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period					(6,000,000)	$ (6,000,000)
Southern Power [Member]
Derivative [Line Items]
Derivative collateral obligation to return cash					0	$ 0
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU						3,000,000
Realized gain (loss) on termination of interest rate derivatives						$ (44,000,000)	$ 0	0
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months						14,000,000
Parent Company and Southern Power [Member]
Derivative [Line Items]
Foreign Currency Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months					$ (25,000,000)	(25,000,000)
Interest rate derivatives
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives						(180,000,000)	(22,000,000)	(16,000,000)
Interest rate derivatives | Gulf Power [Member]
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives						0	1,000,000	0
Interest rate derivatives | Georgia Power [Member]
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives						0	(15,000,000)	(8,000,000)
Interest rate derivatives | Alabama Power [Member]
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives						(3,000,000)	(7,000,000)	(8,000,000)
Interest rate derivatives | Southern Power [Member]
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives						$ 0	0	0
Interest Rate Swap [Member] | Southern Company Gas [Member]
Derivative [Line Items]
Notional Amount	$ 800,000,000
Public Utilities, Inventory, Natural Gas [Member]
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU					500,000,000	500,000,000
Public Utilities, Inventory, Natural Gas [Member] | Georgia Power [Member]
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU					155,000,000	155,000,000
Longest Hedge Date						2020
Public Utilities, Inventory, Natural Gas [Member] | Southern Company Gas [Member]
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU					157,000,000	157,000,000
Public Utilities, Inventory, Natural Gas [Member] | Alabama Power [Member]
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU					74,000,000	74,000,000
Public Utilities, Inventory, Natural Gas [Member] | Southern Power [Member]
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU					27,000,000	27,000,000
Longest Non-Hedge Date						2017
Public Utilities, Inventory, Power Position [Member] | Southern Power [Member]
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU					6,100,000	6,100,000
Public Utilities, Inventory, Fuel [Member]
Derivative [Line Items]
Longest Hedge Date						2020
Longest Non-Hedge Date						2022
Public Utilities, Inventory, Fuel [Member] | Southern Company Gas [Member]
Derivative [Line Items]
Longest Non-Hedge Date						2022
Minimum [Member] | Interest Rate Swap [Member] | Southern Company Gas [Member]
Derivative [Line Items]
Term of contract	10 years
Maximum [Member] | Interest Rate Swap [Member] | Southern Company Gas [Member]
Derivative [Line Items]
Term of contract	30 years
Cash Flow Hedging [Member] | Mississippi Power [Member]
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives						$ 3,000,000	$ 0	$ 0
Cash Flow Hedging [Member] | Interest rate derivatives | Georgia Power [Member]
Derivative [Line Items]
Notional Amount					$ 0	$ 0
Cash Flow Hedging [Member] | Interest Rate Swap [Member] | Southern Company Gas [Member]
Derivative [Line Items]
Derivative, Settlement, Notional Amount		$ 200,000,000	$ 400,000,000	$ 200,000,000					$ 200,000,000
Derivative Instruments, Loss Recognized in Other Comprehensive Income (Loss), Effective Portion		$ 35,000,000	$ 26,000,000
Successor [Member] | Southern Company Gas [Member]
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives					(3,000,000)
Successor [Member] | Interest rate derivatives | Southern Company Gas [Member]
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives					$ (5,000,000)
Successor [Member] | Cash Flow Hedging [Member] | Interest rate derivatives | Southern Company Gas [Member]
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives				$ (5,000,000)