Financing - Narrative (Details) shares in Thousands				1 Months Ended				6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 03, 2015 USD ($)	Feb. 20, 2014	Jun. 30, 2017 USD ($) agreement	May 31, 2017 USD ($) shares	Apr. 30, 2017 USD ($)	Feb. 28, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Short-term debt	$ 3,274,000,000			$ 3,274,000,000				$ 3,274,000,000			$ 2,241,000,000
Variable rate pollution control revenue bonds outstanding	1,600,000,000			1,600,000,000				1,600,000,000
Maximum borrowing capacity	8,168,000,000			8,168,000,000				8,168,000,000
Senior Note Issuances								2,450,000,000
Preference stock redemption								150,000,000
Southern Company
Debt Instrument [Line Items]
Maximum borrowing capacity	2,000,000,000			2,000,000,000	$ 1,250,000,000.00			2,000,000,000
Senior Note Issuances								300,000,000
Southern Company | Senior Notes | Series 2017A
Debt Instrument [Line Items]
Debt face amount	$ 500,000,000			$ 500,000,000				$ 500,000,000
Debt stated interest rate	5.325%			5.325%				5.325%
Southern Company | Senior Notes | Series 2017A Floating Rate Senior Notes
Debt Instrument [Line Items]
Debt face amount	$ 300,000,000			$ 300,000,000				$ 300,000,000
Southern Company | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement
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
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Working capital	930,000,000			930,000,000				930,000,000
Senior notes, current	17,000,000			17,000,000				17,000,000
Short-term debt	17,000,000			17,000,000				17,000,000			23,000,000
Long-term pollution control bond	50,000,000			50,000,000				50,000,000
Variable rate pollution control revenue bonds outstanding	40,000,000			40,000,000				40,000,000
Fixed rate pollution control revenue bonds outstanding	50,000,000			50,000,000				50,000,000
Maximum borrowing capacity	113,000,000			113,000,000				113,000,000
Senior Note Issuances								0
Promissory note		$ 301,000,000
Capital contributions from parent company	1,000,000,000							1,001,000,000	$ 226,000,000
MISSISSIPPI POWER CO | Unsecured Debt
Debt Instrument [Line Items]
Loans payable to bank	935,000,000			935,000,000				935,000,000
MISSISSIPPI POWER CO | Tax-Exempt Variable Rate Demand Obligations
Debt Instrument [Line Items]
Short-term debt	40,000,000			40,000,000				40,000,000
MISSISSIPPI POWER CO | Short Term Note
Debt Instrument [Line Items]
Debt face amount										$ 9,000,000
Debt stated interest rate										5.00%
MISSISSIPPI POWER CO | Bank Loans | Loans Payable [Member]
Debt Instrument [Line Items]
Repayments of debt				10,000,000
MISSISSIPPI POWER CO | Promissory Notes | Promissory Notes
Debt Instrument [Line Items]
Repayments of debt				591,000,000
Increase in debt instrument						$ 40,000,000
MISSISSIPPI POWER CO | Unsecured Debt | Term Loan
Debt Instrument [Line Items]
Debt face amount	1,200,000,000.0			1,200,000,000.0				1,200,000,000.0
Repayments of debt				300,000,000
GEORGIA POWER CO
Debt Instrument [Line Items]
Short-term debt	1,228,000,000			1,228,000,000				1,228,000,000			391,000,000
Debt instrument, basis spread on variable rate			0.375%
Amortization period for line of credit facility			5 years
Variable rate pollution control revenue bonds outstanding	550,000,000			550,000,000				550,000,000
Variable rate pollution control revenue bonds outstanding, amount remarketed	318,000,000			318,000,000				318,000,000
Fixed rate pollution control revenue bonds outstanding	436,000,000			436,000,000				436,000,000
Maximum borrowing capacity	1,750,000,000			1,750,000,000				1,750,000,000
Senior Note Issuances								850,000,000
Capital contributions from parent company								380,000,000	239,000,000
GEORGIA POWER CO | Line of Credit | Uncommitted Bank Credit Arrangement
Debt Instrument [Line Items]
Increase in debt instrument				$ 500,000,000
GEORGIA POWER CO | Senior Notes | Series 2017A
Debt Instrument [Line Items]
Debt face amount										$ 450,000,000
Debt stated interest rate										2.00%
GEORGIA POWER CO | Senior Notes | Series 2017B
Debt Instrument [Line Items]
Debt face amount										$ 400,000,000
Debt stated interest rate										3.25%
GEORGIA POWER CO | Municipal Bonds [Member] | 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						$ 27,000,000
GEORGIA POWER CO | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement
Debt Instrument [Line Items]
Number of loan agreements | agreement				3
Payable to bank by demand, term				30 days
GEORGIA POWER CO | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 1
Debt Instrument [Line Items]
Debt face amount	50,000,000			$ 50,000,000				50,000,000
GEORGIA POWER CO | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 2
Debt Instrument [Line Items]
Debt face amount	150,000,000			150,000,000				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			100,000,000				100,000,000
ALABAMA POWER CO
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding	890,000,000			890,000,000				890,000,000
Maximum borrowing capacity	1,335,000,000			1,335,000,000				1,335,000,000
Senior Note Issuances								550,000,000
Capital contributions from parent company								327,000,000	237,000,000
ALABAMA POWER CO | Senior Notes | Series 2017A
Debt Instrument [Line Items]
Debt face amount	$ 550,000,000			$ 550,000,000				$ 550,000,000
Debt stated interest rate	2.45%			2.45%				2.45%
GULF POWER CO
Debt Instrument [Line Items]
Short-term debt	$ 78,000,000			$ 78,000,000				$ 78,000,000			268,000,000
Variable rate pollution control revenue bonds outstanding	82,000,000			82,000,000				82,000,000
Fixed rate pollution control revenue bonds outstanding	140,000,000			140,000,000				140,000,000
Maximum borrowing capacity	280,000,000			280,000,000				280,000,000
Senior Note Issuances								300,000,000
Capital contributions from parent company								5,000,000	5,000,000
GULF POWER CO | Senior Notes | Series 2017A
Debt Instrument [Line Items]
Debt face amount					$ 300,000,000
Debt stated interest rate					3.30%
GULF POWER CO | Senior Notes | Series 2007A
Debt Instrument [Line Items]
Debt stated interest rate					5.90%
Repayments of debt					$ 85,000,000
GULF POWER CO | Senior Notes | Series Preference Stock
Debt Instrument [Line Items]
Debt stated interest rate					6.00%
Stock redeemed during period (in shares) | shares					550
Preference stock redemption					$ 55,000,000
GULF POWER CO | Senior Notes | Series 2007A Preference Stock
Debt Instrument [Line Items]
Debt stated interest rate					6.45%
Stock redeemed during period (in shares) | shares					450
Preference stock redemption					$ 45,000,000
GULF POWER CO | Senior Notes | Series 2013A Preference Stock
Debt Instrument [Line Items]
Debt stated interest rate					5.60%
Stock redeemed during period (in shares) | shares					500
Preference stock redemption					$ 50,000,000
GULF POWER CO | Senior Notes | Short-term Floating Rate Bank Loan
Debt Instrument [Line Items]
Repayments of debt					100,000,000
GULF POWER CO | Bank Loans
Debt Instrument [Line Items]
Debt face amount										$ 100,000,000
Traditional Electric Operating Companies
Debt Instrument [Line Items]
Fixed rate pollution control revenue bonds outstanding	626,000,000			626,000,000				626,000,000
SOUTHERN POWER CO
Debt Instrument [Line Items]
Short-term debt	398,000,000			398,000,000				398,000,000			209,000,000
Maximum borrowing capacity	750,000,000			750,000,000	600,000,000			750,000,000
Senior Note Issuances								0
Capital contributions from parent company								0	$ 300,000,000
Southern Company Gas Capital
Debt Instrument [Line Items]
Maximum borrowing capacity	1,200,000,000.0			1,200,000,000.0	1,200,000,000.0			1,200,000,000.0
Nicor Gas
Debt Instrument [Line Items]
Maximum borrowing capacity	700,000,000			700,000,000	700,000,000			700,000,000
SOUTHERN Co GAS
Debt Instrument [Line Items]
Short-term debt	626,000,000			626,000,000				626,000,000			$ 1,257,000,000
Maximum borrowing capacity	$ 1,900,000,000			$ 1,900,000,000				1,900,000,000
Senior Note Issuances								450,000,000
Capital contributions from parent company								$ 57,000,000
SOUTHERN Co GAS | Senior Notes | Series 2017A
Debt Instrument [Line Items]
Debt face amount					$ 450,000,000
Debt stated interest rate					4.40%
Southern Company | MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Promissory note							$ 551,000,000
Line of Credit | Southern Company | Line of Credit
Debt Instrument [Line Items]
Extinguishment of debt, amount					$ 1,000,000,000
Line of Credit | Southern Company Gas Capital
Debt Instrument [Line Items]
Termination of Credit Arrangement					1,300,000,000
Line of Credit | Nicor Gas | Line of Credit
Debt Instrument [Line Items]
Termination of Credit Arrangement					$ 700,000,000