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 ($)	Dec. 31, 2017 USD ($) MMBTU	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Nov. 30, 2015 USD ($)
Derivative [Line Items]
Notional amount						$ 3,650,000,000
Derivative collateral obligation to return cash						$ 0
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU						32,000,000
Realized gain (loss) on termination of interest rate derivatives						$ 91,000,000	$ (220,000,000)	$ (22,000,000)
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period						(20,000,000)
Cash flow hedge gain (loss) to be reclassified within twelve months						(11,000,000)
ALABAMA POWER CO
Derivative [Line Items]
Derivative collateral obligation to return cash						$ 0
Longest hedge date						2020
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU						5,000,000
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period						$ (6,000,000)
Fair value of derivative liabilities with contingent features						1,000,000
Cash flow hedge ineffectiveness recorded in earnings						0
Derivative liability, fair value of collateral						$ 12,000,000
GEORGIA POWER CO
Derivative [Line Items]
Required period for options and hedges						48 months
Notional amount						$ 950,000,000
Derivative collateral obligation to return cash						$ 0
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU						10,000,000
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period						$ (4,000,000)
Fair value of derivative liabilities with contingent features						2,000,000
Derivative liability, fair value of collateral						12,000,000
GULF POWER CO
Derivative [Line Items]
Derivative collateral obligation to return cash						$ 0
Net volume of energy-related derivative contracts for natural gas positions | MMBTU						22,000,000
Longest hedge date						2020
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU						3,000,000
Derivative liability, fair value of collateral						$ 12,000,000
MISSISSIPPI POWER CO
Derivative [Line Items]
Increase (Decrease) Cash Collateral from Counterparties						$ 0
Net volume of energy-related derivative contracts for natural gas positions | MMBTU						53,000,000
Longest hedge date						2021
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU						4,000,000
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period						$ (500,000)
Fair value of derivative liabilities with contingent features						1,000,000
Derivative liability, fair value of collateral						12,000,000
SOUTHERN POWER CO
Derivative [Line Items]
Derivative collateral obligation to return cash					$ 0	$ 0	0
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU						10,000,000
Realized gain (loss) on termination of interest rate derivatives						$ 102,000,000	(44,000,000)	0
Fair value of derivative liabilities with contingent features						8,000,000
Cash flow hedge gain (loss) to be reclassified within twelve months						(7,000,000)
Interest rate derivatives outstanding						0
Deferred gain (loss) on interest rate cash flow hedges, accumulated other comprehensive income						0
Cash flow hedge ineffectiveness recorded in earnings						0
Derivative liability, fair value of collateral						12,000,000
SOUTHERN Co GAS
Derivative [Line Items]
Increase (Decrease) Cash Collateral from Counterparties						0
Derivative collateral obligation to return cash						0
Realized gain (loss) on termination of interest rate derivatives					(3,000,000)
Fair value of derivative liabilities with contingent features						3,000,000
Maximum potential collateral requirements arising the from credit-risk-related contingent features						2,000,000
Cash flow hedge gain (loss) to be reclassified within twelve months						4,000,000
Parent Company and Southern Power
Derivative [Line Items]
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months						(23,000,000)
Interest rate derivatives
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives						(2,000,000)	(180,000,000)	(22,000,000)
Fair value of derivative liabilities with contingent features						7,000,000
Interest rate derivatives | ALABAMA POWER CO
Derivative [Line Items]
Notional amount						0
Realized gain (loss) on termination of interest rate derivatives						0	(3,000,000)	(7,000,000)
Interest rate derivatives | GEORGIA POWER CO
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives						1,000,000	0	(15,000,000)
Interest rate derivatives | GULF POWER CO
Derivative [Line Items]
Notional amount						0
Interest rate derivatives | SOUTHERN POWER CO
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives						$ 0	0	0
Interest rate derivatives | SOUTHERN Co GAS
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives					(5,000,000)
Interest Rate Swap | SOUTHERN Co GAS
Derivative [Line Items]
Notional amount	$ 800,000,000
Public Utilities, Inventory, Natural Gas
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU						621,000,000
Public Utilities, Inventory, Natural Gas | ALABAMA POWER CO
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU						69,000,000
Public Utilities, Inventory, Natural Gas | GEORGIA POWER CO
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU						163,000,000
Longest hedge date						2021
Public Utilities, Inventory, Natural Gas | SOUTHERN POWER CO
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU						14,000,000
Longest non-hedge date						2018
Public Utilities, Inventory, Natural Gas | SOUTHERN Co GAS
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU						300,000,000
Public Utilities, Inventory, Power Position | SOUTHERN POWER CO
Derivative [Line Items]
Net volume of energy-related derivative contracts for natural gas positions | MMBTU						3,000,000
Public Utilities, Inventory, Fuel
Derivative [Line Items]
Longest hedge date						2021
Longest non-hedge date						2026
Public Utilities, Inventory, Fuel | SOUTHERN Co GAS
Derivative [Line Items]
Longest hedge date						2020
Longest non-hedge date						2026
Energy-related derivatives
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives						$ (47,000,000)	18,000,000	0
Fair value of derivative liabilities with contingent features						15,000,000
Derivative liability, fair value of collateral						14,000,000
Energy-related derivatives | SOUTHERN POWER CO
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives						(38,000,000)	14,000,000	0
Energy-related derivatives | SOUTHERN Co GAS
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives					$ 2,000,000	(9,000,000)
Minimum | Interest Rate Swap | SOUTHERN Co GAS
Derivative [Line Items]
Term of contract	10 years
Maximum | Interest Rate Swap | SOUTHERN Co GAS
Derivative [Line Items]
Term of contract	30 years
Cash Flow Hedging | MISSISSIPPI POWER CO
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives						0	$ 0	$ 0
Cash Flow Hedging | Interest rate derivatives | GEORGIA POWER CO
Derivative [Line Items]
Notional amount						$ 0
Cash Flow Hedging | Interest rate derivatives | SOUTHERN Co GAS
Derivative [Line Items]
Realized gain (loss) on termination of interest rate derivatives				$ (5,000,000)
Cash Flow Hedging | Interest Rate Swap | SOUTHERN Co GAS
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