Derivatives - Narrative (Details) MMBTU in Millions	3 Months Ended
	Mar. 31, 2023 USD ($) MMBTU	Dec. 31, 2022 USD ($)
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	22
Energy-related derivative hedge gain (loss) to be reclassified within twelve months	$ (42,000,000)
Collateral already posted, assets, aggregate fair value	60,000,000
Derivatives	756,000,000	$ 617,000,000
Interest rate derivatives
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified within twelve months	(15,000,000)
Derivatives	$ 73,000,000
SOUTHERN POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	5
Energy-related derivative hedge gain (loss) to be reclassified within twelve months	$ (12,000,000)
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months	(11,000,000)
Collateral already posted, assets, aggregate fair value	15,000,000
Derivatives	61,000,000	59,000,000
SOUTHERN POWER CO | Interest rate derivatives
Derivative [Line Items]
Derivatives	23,000,000
SOUTHERN Co GAS
Derivative [Line Items]
Energy-related derivative hedge gain (loss) to be reclassified within twelve months	(30,000,000)
Collateral already posted, assets, aggregate fair value	60,000,000	41,000,000
Derivatives	$ 119,000,000	110,000,000
ALABAMA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	6
Energy-related derivative hedge gain (loss) to be reclassified within twelve months	$ 0
Collateral already posted, assets, aggregate fair value	0
Derivatives	$ 68,000,000	15,000,000
GEORGIA POWER CO
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | MMBTU	8
Energy-related derivative hedge gain (loss) to be reclassified within twelve months	$ 0
Derivatives	$ 114,000,000	41,000,000
MISSISSIPPI 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
Derivatives	37,000,000	$ 15,000,000
Registrants | Derivative Counterparties
Derivative [Line Items]
Collateral already posted, assets, aggregate fair value	$ 0