Contingencies and Regulatory Matters - General (Details) $ in Thousands						6 Months Ended
	Jun. 12, 2018 USD ($)	May 18, 2018 USD ($)	May 14, 2018 USD ($)	Mar. 02, 2018 USD ($) generating_plant	Feb. 07, 2018	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
ALABAMA POWER CO
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage						46.60%
MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Public utilities, requested return on equity, percentage					9.33%
GEORGIA POWER CO
Loss Contingencies [Line Items]
Environmental remediation liability						$ 25,000	$ 22,000
GULF POWER CO
Loss Contingencies [Line Items]
Environmental remediation liability						48,000	52,000
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental remediation liability						$ 305,000	388,000
RE Roserock, LLC | SOUTHERN POWER CO
Loss Contingencies [Line Items]
Ownership percentage by parent						51.00%
Location One | SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental remediation liability						$ 2,000
Location One | SOUTHERN Co GAS | Elizabethtown Gas
Loss Contingencies [Line Items]
Environmental remediation liability						$ 77,000	$ 85,000
Alabama Department of Environmental Management (ADEM) | ALABAMA POWER CO
Loss Contingencies [Line Items]
Litigation settlement, amount awarded to other party				$ 1,250
Number of electric generating plants | generating_plant				5
Deepwater Horizon Oil Spill Litigation Case | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Litigation settlement awarded from other party			$ 18,000
Martin Product Sales, LLC Litigation | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Damages sought by litigation		$ 143,000
Nicor Energy Services Company Litigation | SOUTHERN Co GAS
Loss Contingencies [Line Items]
Litigation amount awarded to other party	$ 11,000
Open Access Transmission Tariff
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage						11.25%
Public utilities, requested return on equity, percentage						8.65%