Derivatives - Narrative (Details) MMBTU in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) MMBTU	Jun. 30, 2022 USD ($)	Jun. 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			11
Collateral already posted, assets, aggregate fair value	$ 52,000,000		$ 52,000,000
Derivatives	693,000,000		693,000,000			$ 617,000,000
Gain (Loss) Recognized in OCI on Derivatives	36,000,000	$ (61,000,000)	(50,000,000)	$ (34,000,000)
Scenario, Forecast
Derivative [Line Items]
Energy-related derivative hedge gain (loss) to be reclassified within twelve months					$ 33,000,000
Interest rate derivatives
Derivative [Line Items]
Derivatives	65,000,000		65,000,000
Interest rate derivatives | Scenario, Forecast
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months					(15,000,000)
Interest rate derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	3,000,000	21,000,000	(10,000,000)	30,000,000
Energy-related derivatives | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	16,000,000	(40,000,000)	29,000,000	(18,000,000)
Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(5,000,000)	(1,000,000)	$ (50,000,000)	41,000,000
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
Foreign currency cash flow hedge gain (loss to be reclassified	11,000,000		$ 11,000,000
Collateral already posted, assets, aggregate fair value	15,000,000		15,000,000
Derivatives	37,000,000		37,000,000			59,000,000
Gain (Loss) Recognized in OCI on Derivatives	6,000,000	(72,000,000)	(4,000,000)	(95,000,000)
SOUTHERN POWER CO | Scenario, Forecast
Derivative [Line Items]
Energy-related derivative hedge gain (loss) to be reclassified within twelve months					9,000,000
SOUTHERN POWER CO | Interest rate derivatives
Derivative [Line Items]
Derivatives	13,000,000		13,000,000
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 | Not Designated as Hedging Instrument [Member]
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	(2,000,000)	2,000,000	(13,000,000)	7,000,000
SOUTHERN Co GAS
Derivative [Line Items]
Collateral already posted, assets, aggregate fair value	52,000,000		52,000,000			41,000,000
Derivatives	110,000,000		110,000,000			110,000,000
Gain (Loss) Recognized in OCI on Derivatives	0	(7,000,000)	(33,000,000)	30,000,000
SOUTHERN Co GAS | Scenario, Forecast
Derivative [Line Items]
Energy-related derivative hedge gain (loss) to be reclassified within twelve months					24,000,000
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	3,000,000	(5,000,000)	4,000,000	(5,000,000)
SOUTHERN Co GAS | Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(3,000,000)	(2,000,000)	$ (37,000,000)	35,000,000
ALABAMA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU			3
Collateral already posted, assets, aggregate fair value	0		$ 0
Derivatives	64,000,000		64,000,000			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 | Not Designated as Hedging Instrument [Member]
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			4
Derivatives	90,000,000		$ 90,000,000			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	(1,000,000)	19,000,000	(3,000,000)	31,000,000
GEORGIA POWER CO | Energy-related derivatives | Not Designated as Hedging Instrument [Member]
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			1
Derivatives	36,000,000		$ 36,000,000			$ 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 | Not Designated as Hedging Instrument [Member]
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