Derivatives - Narrative (Details) MMBTU in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($) MMBTU	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU			13
Gain (Loss) Recognized in OCI on Derivatives	$ (2,000,000)	$ 5,000,000	$ (7,000,000)	$ (45,000,000)
Collateral already posted, assets, aggregate fair value	22,000,000		22,000,000
Derivatives	469,000,000		469,000,000		$ 659,000,000
Interest rate derivatives
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months	(14,000,000)		(14,000,000)
Derivatives	61,000,000		61,000,000
Interest rate derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(8,000,000)	(3,000,000)	16,000,000	(12,000,000)
Interest rate derivatives | Cash Flow Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(4,000,000)	(22,000,000)	(12,000,000)	(31,000,000)
Interest rate derivatives | Fair Value Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	78,000,000	(47,000,000)	47,000,000	(50,000,000)
Energy-related derivatives | Energy-related derivatives not designated as hedging instruments | Cost of Natural Gas
Derivative [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	6,000,000	7,000,000	69,000,000	36,000,000
Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(7,000,000)	(4,000,000)	(11,000,000)	(55,000,000)
Foreign currency derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	15,000,000	(15,000,000)	(4,000,000)	(6,000,000)
Foreign currency derivatives | Cash Flow Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(3,000,000)	(3,000,000)	(9,000,000)	(8,000,000)
Foreign currency derivatives | Fair Value Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(2,000,000)	27,000,000	$ (8,000,000)	28,000,000
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
Energy-related derivative hedge gain (loss) to be reclassified within twelve months	0		$ 0
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months	0		0
Gain (Loss) Recognized in OCI on Derivatives	13,000,000	(15,000,000)	(6,000,000)	(20,000,000)
Collateral already posted, assets, aggregate fair value	0		0
Derivatives	16,000,000		16,000,000		27,000,000
SOUTHERN POWER CO | Interest rate derivatives
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months	0		0
Derivatives	0		0
SOUTHERN POWER CO | Energy-related derivatives
Derivative [Line Items]
Derivatives	0		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	(2,000,000)	0	(2,000,000)	(14,000,000)
SOUTHERN POWER CO | Foreign currency derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	15,000,000	(15,000,000)	(4,000,000)	(6,000,000)
SOUTHERN POWER CO | Foreign currency derivatives | Cash Flow Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(3,000,000)	(3,000,000)	(9,000,000)	(8,000,000)
SOUTHERN Co GAS
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(10,000,000)	(8,000,000)	(14,000,000)	(41,000,000)
Collateral already posted, assets, aggregate fair value	22,000,000		22,000,000		62,000,000
Derivatives	63,000,000		63,000,000		87,000,000
SOUTHERN Co GAS | Interest rate derivatives
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months	0		0
SOUTHERN Co GAS | Interest rate derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(6,000,000)	(4,000,000)	(5,000,000)	0
SOUTHERN Co GAS | Interest rate derivatives | Cash Flow Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	0	(18,000,000)	0	(18,000,000)
SOUTHERN Co GAS | Interest rate derivatives | Fair Value Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	28,000,000	(11,000,000)	18,000,000	(14,000,000)
SOUTHERN Co GAS | Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(4,000,000)	(4,000,000)	$ (9,000,000)	(41,000,000)
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	52,000,000		52,000,000		100,000,000
ALABAMA POWER CO | Interest rate derivatives
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months	0		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	54,000,000		$ 54,000,000		113,000,000
GEORGIA POWER CO | Interest rate derivatives
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months	0		0
GEORGIA POWER CO | Interest rate derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	1,000,000	0	17,000,000	(3,000,000)
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	38,000,000		$ 38,000,000		$ 47,000,000
MISSISSIPPI POWER CO | Interest rate derivatives
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months	0		0
MISSISSIPPI POWER CO | Interest rate derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	0	0	7,000,000	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
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
Traditional Electric Operating Companies | Energy-related derivatives
Derivative [Line Items]
Derivatives	$ 0		$ 0