Financing - Narrative (Details) - USD ($)		1 Months Ended
	May 02, 2018	Mar. 31, 2018	May 23, 2018	Jan. 31, 2018	Jan. 04, 2018	Jul. 31, 2017
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding		$ 1,500,000,000
Maximum borrowing capacity		8,145,000,000
Floating rate Promissory Note Due July 2018
Debt Instrument [Line Items]
Debt face amount					$ 100,000,000
Southern Company
Debt Instrument [Line Items]
Maximum borrowing capacity		2,000,000,000
Southern Company | Floating Rate Bank Term Loan Agreement 1 | Notes Payable to Banks
Debt Instrument [Line Items]
Debt face amount		900,000,000
ALABAMA POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding		854,000,000
Fixed rate pollution control revenue bonds outstanding		120,000,000
Maximum borrowing capacity		1,335,000,000
GEORGIA POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding		550,000,000
Fixed rate pollution control revenue bonds outstanding		192,000,000
Maximum borrowing capacity		1,750,000,000
GEORGIA POWER CO | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 2
Debt Instrument [Line Items]
Debt face amount				$ 150,000,000
GEORGIA POWER CO | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 3
Debt Instrument [Line Items]
Debt face amount				$ 100,000,000
GEORGIA POWER CO | Municipal Bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Fifth Series 1995
Debt Instrument [Line Items]
Debt face amount		104,600,000.0
GEORGIA POWER CO | Municipal Bonds | Development Authority of Bartow County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Bowen Project), First Series 1997
Debt Instrument [Line Items]
Debt face amount		173,000,000
GULF POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding		82,000,000
Fixed rate pollution control revenue bonds outstanding		75,000,000
Maximum borrowing capacity		280,000,000
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding		40,000,000
Fixed rate pollution control revenue bonds outstanding		50,000,000
Maximum borrowing capacity		100,000,000
MISSISSIPPI POWER CO | Notes Payable to Banks
Debt Instrument [Line Items]
Debt face amount		300,000,000
MISSISSIPPI POWER CO | Senior Notes | Series 2018A Floating Rate Senior Notes
Debt Instrument [Line Items]
Debt face amount		300,000,000
MISSISSIPPI POWER CO | Senior Notes | Series 2018B 3.95% Senior Notes
Debt Instrument [Line Items]
Debt face amount		$ 300,000,000
Debt stated interest rate		3.95%
MISSISSIPPI POWER CO | Unsecured Debt | Unsecured Term Loan
Debt Instrument [Line Items]
Repayments of debt		$ 900,000,000
Traditional Electric Operating Companies
Debt Instrument [Line Items]
Fixed rate pollution control revenue bonds outstanding		437,000,000
SOUTHERN Co GAS
Debt Instrument [Line Items]
Maximum borrowing capacity		1,900,000,000
Nicor Gas
Debt Instrument [Line Items]
Maximum borrowing capacity		500,000,000
Nicor Gas | Collateralized Mortgage Backed Securities [Member] | First Mortgage Bonds
Debt Instrument [Line Items]
Debt face amount						$ 181,000,000
Maximum borrowing capacity		$ 181,000,000
Subsequent Event | GEORGIA POWER CO | Municipal Bonds | Pollution Control Revenue Bonds
Debt Instrument [Line Items]
Debt instrument, repurchase amount	$ 55,000,000
Subsequent Event | MISSISSIPPI POWER CO | Promissory Notes | Promissory Notes
Debt Instrument [Line Items]
Proceeds from Issuance of Debt	125,000,000
Subsequent Event | SOUTHERN Co GAS | Senior Notes | Series 2017A
Debt Instrument [Line Items]
Debt face amount	$ 20,000,000
Scenario, Forecast | SOUTHERN Co GAS | Senior Notes | Series 2017A
Debt Instrument [Line Items]
Debt face amount			$ 180,000,000