Contingencies - General Litigation Matters (Details) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended	16 Months Ended
	Mar. 31, 2019 plaintiff	Mar. 31, 2022 USD ($)	Dec. 31, 2018 USD ($) defendant plaintiff	Jan. 31, 2023 claim	Sep. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2021 project	Dec. 31, 2016 USD ($)	Dec. 31, 2010 USD ($)
MISSISSIPPI POWER CO | Kemper IGCC
Loss Contingencies [Line Items]
DOE awards								$ 137.0	$ 270.0
Government grants received			$ 387.0
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
GEORGIA POWER CO | Pending Litigation | Class Action Lawsuit
Loss Contingencies [Line Items]
Complaints filed | claim				8
SOUTHERN POWER CO | Proceeds From Issuance Of Solid Waste Disposal Facility Revenue Bonds
Loss Contingencies [Line Items]
Restricted cash					$ 16.0	$ 17.0
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