Financing - Narrative (Details)			1 Months Ended				3 Months Ended	6 Months Ended
	Aug. 07, 2018 USD ($)	May 20, 2018	Jun. 30, 2018 USD ($) agreement	May 31, 2018 USD ($) agreement	Apr. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Jan. 31, 2018 USD ($)	Jan. 04, 2018 USD ($)	Sep. 30, 2017 USD ($)
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding			$ 1,500,000,000				$ 1,500,000,000	$ 1,500,000,000
Maximum borrowing capacity			8,143,000,000				8,143,000,000	8,143,000,000
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				2,000,000,000	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
Southern Company | Uncommitted Bank Credit Arrangement | Notes Payable to Banks
Debt Instrument [Line Items]
Debt face amount					$ 250,000,000
Debt instrument, payable by demand from bank, term					30 days
Southern Company | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 1
Debt Instrument [Line Items]
Number of loan agreements | agreement			2
Southern Company | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 4
Debt Instrument [Line Items]
Debt face amount			$ 100,000,000				100,000,000	100,000,000
Southern Company | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 5
Debt Instrument [Line Items]
Debt face amount			100,000,000				100,000,000	100,000,000
ALABAMA POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding			854,000,000				854,000,000	854,000,000
Fixed rate pollution control revenue bonds outstanding			120,000,000				120,000,000	120,000,000
Maximum borrowing capacity			1,333,000,000				1,333,000,000	1,333,000,000
ALABAMA POWER CO | Senior Notes | Series 2018A Floating Rate Senior Notes
Debt Instrument [Line Items]
Debt face amount			$ 500,000,000				$ 500,000,000	$ 500,000,000
Debt stated interest rate			4.30%				4.30%	4.30%
ALABAMA POWER CO | Senior Notes | Series 2008B 5.40% Senior Notes due June 1, 2018
Debt Instrument [Line Items]
Debt stated interest rate					5.40%
Repurchased face amount					$ 250,000,000
GEORGIA POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding			$ 550,000,000				$ 550,000,000	$ 550,000,000
Fixed rate pollution control revenue bonds outstanding			232,000,000				232,000,000	232,000,000
Maximum borrowing capacity			1,750,000,000				1,750,000,000	$ 1,750,000,000
Amortization period for line of credit facility								5 years
Percent of eligible project costs to be reimbursed								70.00%
GEORGIA POWER CO | Loan Guarantee Agreement
Debt Instrument [Line Items]
Conditional borrowing commitment											$ 1,670,000,000
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 | Senior Notes
Debt Instrument [Line Items]
Repayments of debt				$ 902,000,000
GEORGIA POWER CO | Senior Notes | Series 2007A 5.65% Senior Notes
Debt Instrument [Line Items]
Debt instrument, repurchase amount				89,000,000
Debt face amount				$ 250,000,000
Debt stated interest rate				5.65%
GEORGIA POWER CO | Senior Notes | Series 2009A 5.95% Senior Notes
Debt Instrument [Line Items]
Debt instrument, repurchase amount				$ 326,000,000
Debt face amount				$ 500,000,000
Debt stated interest rate				5.95%
GEORGIA POWER CO | Senior Notes | Series 2010B 5.40% Senior Notes
Debt Instrument [Line Items]
Debt instrument, repurchase amount				$ 335,000,000
Debt face amount				$ 600,000,000
Debt stated interest rate				5.40%
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
GEORGIA POWER CO | Municipal Bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Fifth Series 1994
Debt Instrument [Line Items]
Debt face amount					$ 55,000,000
GEORGIA POWER CO | Municipal Bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Second Series 2008
Debt Instrument [Line Items]
Debt face amount			65,000,000				65,000,000	$ 65,000,000
GULF POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding			82,000,000				82,000,000	82,000,000
Fixed rate pollution control revenue bonds outstanding			37,000,000				37,000,000	37,000,000
Maximum borrowing capacity			280,000,000				280,000,000	280,000,000
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding			40,000,000				40,000,000	40,000,000
Fixed rate pollution control revenue bonds outstanding			93,000,000				93,000,000	93,000,000
Maximum borrowing capacity			100,000,000				100,000,000	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 | Promissory Notes | Promissory Notes
Debt Instrument [Line Items]
Repayments of debt							200,000,000
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			482,000,000				482,000,000	482,000,000
SOUTHERN POWER CO
Debt Instrument [Line Items]
Repayments of debt				$ 770,000,000
Maximum borrowing capacity			750,000,000				750,000,000	750,000,000
SOUTHERN POWER CO | Floating Rate Bank Term Loan Agreement 1 | Notes Payable to Banks
Debt Instrument [Line Items]
Debt face amount				$ 100,000,000
Number of loan agreements | agreement				2
Repurchased face amount			$ 420,000,000				$ 420,000,000	$ 420,000,000
SOUTHERN POWER CO | Senior Notes | Series 2015A 1.50% Senior Notes
Debt Instrument [Line Items]
Debt stated interest rate			1.50%				1.50%	1.50%
Repurchased face amount			$ 350,000,000				$ 350,000,000	$ 350,000,000
SOUTHERN Co GAS
Debt Instrument [Line Items]
Maximum borrowing capacity			1,900,000,000				1,900,000,000	1,900,000,000
SOUTHERN Co GAS | Uncommitted Bank Credit Arrangement | Notes Payable to Banks
Debt Instrument [Line Items]
Debt face amount				$ 95,000,000
Debt instrument, payable by demand from bank, term				30 days
SOUTHERN Co GAS | Senior Notes | Series 2017A
Debt Instrument [Line Items]
Debt face amount			200,000,000				200,000,000	200,000,000
Nicor Gas
Debt Instrument [Line Items]
Maximum borrowing capacity			500,000,000				500,000,000	500,000,000
Nicor Gas | Collateralized Mortgage Backed Securities | First Mortgage Bonds
Debt Instrument [Line Items]
Debt face amount			181,000,000				$ 181,000,000	181,000,000
Subsequent Event | MISSISSIPPI POWER CO | Municipal Bonds | Pollution Control Revenue Bonds
Debt Instrument [Line Items]
Debt instrument, repurchase amount	$ 43,000,000
Subsequent Event | MISSISSIPPI POWER CO | Promissory Notes | Promissory Notes
Debt Instrument [Line Items]
Repayments of debt	$ 50,000,000
SP Solar Holdings I, LP | SOUTHERN POWER CO
Debt Instrument [Line Items]
Limited liability company or limited partnership, members or limited partners, ownership interest		33.00%		33.00%			33.00%
FFB Loan | GEORGIA POWER CO
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 2,600,000,000				$ 2,600,000,000	$ 2,600,000,000
Conditional borrowing commitment											$ 1,670,000,000