Contingencies - General Litigation Matters (Details) $ in Millions	1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended	16 Months Ended
	Jul. 31, 2023 USD ($)	Mar. 31, 2019 plaintiff	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2018 USD ($) defendant plaintiff	Jan. 31, 2023 claim	Jul. 31, 2021 project
Loss Contingencies [Line Items]
Amount awarded					$ 18.0
Increase in other revenues			$ 6,980.0	$ 8,378.0	19,208.0	$ 22,232.0
Allocation to NCI			10.0	12.0	(68.0)	(55.0)
Other revenues
Loss Contingencies [Line Items]
Increase in other revenues			222.0	178.0	662.0	519.0
GEORGIA POWER CO
Loss Contingencies [Line Items]
Increase in other revenues			3,237.0	3,889.0	7,805.0	9,218.0
GEORGIA POWER CO | Other revenues
Loss Contingencies [Line Items]
Increase in other revenues			172.0	130.0	516.0	403.0
GEORGIA POWER CO | Pending Litigation | Class Action Lawsuit
Loss Contingencies [Line Items]
Complaints filed | claim								8
MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Increase in other revenues			436.0	510.0	1,137.0	1,279.0
MISSISSIPPI POWER CO | Other revenues
Loss Contingencies [Line Items]
Increase in other revenues			10.0	13.0	31.0	34.0
MISSISSIPPI POWER CO | Pending Litigation | Purported Violations of Mississippi Consumer Protection Act
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff							10
Number of defendants | defendant							3
Number of additional plaintiffs | plaintiff		4
Underpayment of refunds							$ 23.5
SOUTHERN POWER CO
Loss Contingencies [Line Items]
Amount awarded			18.0
Increase in other revenues			653.0	1,180.0	1,686.0	2,618.0
Allocation to NCI			10.0	12.0	(68.0)	(55.0)
SOUTHERN POWER CO | Other revenues
Loss Contingencies [Line Items]
Increase in other revenues			18.0	$ 9.0	$ 46.0	$ 27.0
SOUTHERN POWER CO | Settled Litigation | Southern Power vs First Solar
Loss Contingencies [Line Items]
Number of solar projects | project									5
Proceeds from legal settlements	$ 36.0
Amount awarded	$ 18.0		18.0
Reduction to other operations and maintenance expense			11.0
Allocation to NCI			6.0
SOUTHERN POWER CO | Settled Litigation | Southern Power vs First Solar | Other revenues
Loss Contingencies [Line Items]
Increase in other revenues			$ 7.0