Derivatives - Narrative (Details) MMBTU in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) MMBTU	Sep. 30, 2022 USD ($)	Sep. 30, 2024 USD ($)	Dec. 31, 2022 USD ($)
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU			14
Gain (Loss) Recognized in OCI on Derivatives	$ 5,000,000	$ 2,000,000	$ (45,000,000)	$ (32,000,000)
Collateral already posted, assets, aggregate fair value	49,000,000		49,000,000
Derivatives	708,000,000		708,000,000			$ 617,000,000
Scenario, Forecast
Derivative [Line Items]
Energy-related derivative hedge gain (loss) to be reclassified within twelve months					$ 30,000,000
Interest rate derivatives
Derivative [Line Items]
Derivatives	78,000,000		78,000,000
Interest rate derivatives | Scenario, Forecast
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months					19,000,000
Interest rate derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(3,000,000)	6,000,000	(12,000,000)	36,000,000
Interest rate derivatives | Cash Flow Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(22,000,000)	(7,000,000)	(31,000,000)	(19,000,000)
Interest rate derivatives | Fair Value Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(47,000,000)	(102,000,000)	(50,000,000)	(300,000,000)
Energy-related derivatives | Energy-related derivatives not designated as hedging instruments
Derivative [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	7,000,000	1,000,000	36,000,000	(17,000,000)
Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(4,000,000)	11,000,000	$ (55,000,000)	51,000,000
SOUTHERN POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU			3
Gain (Loss) Recognized in OCI on Derivatives	(15,000,000)	(46,000,000)	$ (20,000,000)	(141,000,000)
Collateral already posted, assets, aggregate fair value	18,000,000		18,000,000
Derivatives	47,000,000		47,000,000			59,000,000
SOUTHERN POWER CO | Scenario, Forecast
Derivative [Line Items]
Foreign currency cash flow hedge gain (loss to be reclassified					10,000,000
SOUTHERN POWER CO | Interest rate derivatives
Derivative [Line Items]
Derivatives	20,000,000		20,000,000
SOUTHERN POWER CO | Interest rate derivatives | Scenario, Forecast
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months					0
SOUTHERN POWER CO | Energy-related derivatives | Energy-related derivatives not designated as hedging instruments
Derivative [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	0	0	0	0
SOUTHERN POWER CO | Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	0	(11,000,000)	(14,000,000)	(4,000,000)
SOUTHERN Co GAS
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(8,000,000)	27,000,000	(41,000,000)	55,000,000
Collateral already posted, assets, aggregate fair value	49,000,000		49,000,000			41,000,000
Derivatives	102,000,000		102,000,000			110,000,000
SOUTHERN Co GAS | Scenario, Forecast
Derivative [Line Items]
Energy-related derivative hedge gain (loss) to be reclassified within twelve months					25,000,000
SOUTHERN Co GAS | Interest rate derivatives | Scenario, Forecast
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months					0
SOUTHERN Co GAS | Interest rate derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(4,000,000)	5,000,000	0	0
SOUTHERN Co GAS | Interest rate derivatives | Cash Flow Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(18,000,000)	(2,000,000)	(18,000,000)	(3,000,000)
SOUTHERN Co GAS | Interest rate derivatives | Fair Value Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(11,000,000)	(30,000,000)	(14,000,000)	(87,000,000)
SOUTHERN Co GAS | Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(4,000,000)	22,000,000	$ (41,000,000)	55,000,000
ALABAMA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU			4
Collateral already posted, assets, aggregate fair value	0		$ 0
Derivatives	58,000,000		58,000,000			15,000,000
ALABAMA POWER CO | Interest rate derivatives | Scenario, Forecast
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months					0
ALABAMA POWER CO | Energy-related derivatives | Energy-related derivatives not designated as hedging instruments
Derivative [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	0	0	0	0
ALABAMA POWER CO | Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	0	0	$ 0	0
GEORGIA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU			5
Derivatives	72,000,000		$ 72,000,000			41,000,000
GEORGIA POWER CO | Interest rate derivatives | Scenario, Forecast
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months					0
GEORGIA POWER CO | Interest rate derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	0	0	(3,000,000)	31,000,000
GEORGIA POWER CO | Energy-related derivatives | Energy-related derivatives not designated as hedging instruments
Derivative [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	0	0	$ 0	0
MISSISSIPPI POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU			2
Derivatives	27,000,000		$ 27,000,000			$ 15,000,000
MISSISSIPPI POWER CO | Interest rate derivatives | Scenario, Forecast
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months					$ 0
MISSISSIPPI POWER CO | Energy-related derivatives | Energy-related derivatives not designated as hedging instruments
Derivative [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	0	0	0	0
MISSISSIPPI POWER CO | Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	0	0	0	0
Registrants | Derivative Counterparties
Derivative [Line Items]
Collateral already posted, assets, aggregate fair value	0		0
Traditional Electric Operating Companies | Interest rate derivatives | Cash Flow Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	0	0	0	0
Traditional Electric Operating Companies | Interest rate derivatives | Fair Value Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	$ 0	$ 0	$ 0	$ 0