Derivatives - Narrative (Details) MMBTU in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) MMBTU	Mar. 31, 2023 USD ($)	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
Energy-related derivative hedge gain (loss) to be reclassified within twelve months	$ 20,000,000
Gain (Loss) Recognized in OCI on Derivatives	1,000,000	$ (86,000,000)
Collateral already posted, assets, aggregate fair value	54,000,000
Derivatives	718,000,000		$ 659,000,000
Interest rate derivatives
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months	(17,000,000)
Derivatives	66,000,000
Interest rate derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	23,000,000	(13,000,000)
Interest rate derivatives | Cash Flow Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(4,000,000)	(4,000,000)
Interest rate derivatives | Fair Value Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(31,000,000)	43,000,000
Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(8,000,000)	(45,000,000)
Foreign currency derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(14,000,000)	0
Foreign currency derivatives | Cash Flow Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(3,000,000)	(3,000,000)
Foreign currency derivatives | Fair Value Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	$ 0	(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
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months	0
Gain (Loss) Recognized in OCI on Derivatives	(15,000,000)	(11,000,000)
Collateral already posted, assets, aggregate fair value	13,000,000
Derivatives	41,000,000		27,000,000
SOUTHERN POWER CO | Interest rate derivatives
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months	0
Derivatives	17,000,000
SOUTHERN POWER CO | Energy-related derivatives
Derivative [Line Items]
Derivatives	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
SOUTHERN POWER CO | Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(1,000,000)	(11,000,000)
SOUTHERN POWER CO | Foreign currency derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	(14,000,000)	0
SOUTHERN POWER CO | Foreign currency derivatives | Cash Flow Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(3,000,000)	(3,000,000)
SOUTHERN Co GAS
Derivative [Line Items]
Energy-related derivative hedge gain (loss) to be reclassified within twelve months	16,000,000
Gain (Loss) Recognized in OCI on Derivatives	(7,000,000)	(33,000,000)
Collateral already posted, assets, aggregate fair value	54,000,000		62,000,000
Derivatives	92,000,000		87,000,000
SOUTHERN Co GAS | Interest rate derivatives
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months	0
SOUTHERN Co GAS | Interest rate derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	0	1,000,000
SOUTHERN Co GAS | Interest rate derivatives | Cash Flow Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	0	(1,000,000)
SOUTHERN Co GAS | Interest rate derivatives | Fair Value Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(4,000,000)	13,000,000
SOUTHERN Co GAS | Energy-related derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	$ (7,000,000)	(34,000,000)
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
Derivatives	92,000,000		100,000,000
ALABAMA POWER CO | Interest rate derivatives
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months	0
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
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	$ 104,000,000		113,000,000
GEORGIA POWER CO | Interest rate derivatives
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months	0
GEORGIA POWER CO | Interest rate derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	16,000,000	(1,000,000)
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
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	$ 47,000,000		$ 47,000,000
MISSISSIPPI POWER CO | Interest rate derivatives
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months	0
MISSISSIPPI POWER CO | Interest rate derivatives | Cash Flow Hedging
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivatives	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
Registrants | Derivative Counterparties
Derivative [Line Items]
Collateral already posted, assets, aggregate fair value	0
Traditional Electric Operating Companies | Interest rate derivatives | Cash Flow Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	0	0
Traditional Electric Operating Companies | Interest rate derivatives | Fair Value Hedging | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	0	$ 0
Traditional Electric Operating Companies | Energy-related derivatives
Derivative [Line Items]
Derivatives	$ 0