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Financing - Narrative (Details)				1 Months Ended				3 Months Ended	9 Months Ended
Financing - Narrative (Details)	Jun. 27, 2016 USD ($)	Mar. 08, 2016 USD ($)	Jan. 28, 2016 USD ($)	Sep. 30, 2016 USD ($)	May 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Jan. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Jul. 10, 2016	Jul. 01, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2016 EUR (€)	May 24, 2016 USD ($)	Jan. 19, 2016 USD ($)	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding				$ 1,900,000,000				$ 1,900,000,000	$ 1,900,000,000
Maximum borrowing capacity				8,445,000,000				8,445,000,000	8,445,000,000
Senior note issuances									11,981,000,000
Remaining borrowing capacity				8,281,000,000				8,281,000,000	8,281,000,000
Bridge Agreement [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity															$ 8,100,000,000.0
Southern Natural Gas Company, LLC [Member]
Debt Instrument [Line Items]
Noncontrolling interest, ownership percentage by parent											50.00%
Alabama Power [Member]
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding				890,000,000				890,000,000	890,000,000
Fixed rate pollution control revenue bonds outstanding				87,000,000				87,000,000	87,000,000
Maximum borrowing capacity				1,335,000,000				1,335,000,000	1,335,000,000
Senior note issuances									400,000,000
Repayments of senior debt									200,000,000	$ 250,000,000
Capital contributions									253,000,000	13,000,000
Remaining borrowing capacity				1,335,000,000				1,335,000,000	1,335,000,000
Alabama Power [Member] \| Series FF [Member]
Debt Instrument [Line Items]
Debt stated interest rate							5.20%
Alabama Power [Member] \| Senior Notes [Member] \| Series 2016A [Member]
Debt Instrument [Line Items]
Debt face amount							$ 400,000,000
Debt stated interest rate							4.30%
Alabama Power [Member] \| Unsecured Debt [Member] \| Series FF [Member]
Debt Instrument [Line Items]
Repayments of senior debt							$ 200,000,000
Alabama Power [Member] \| Bank Loans [Member]
Debt Instrument [Line Items]
Debt face amount						$ 45,000,000
Debt stated interest rate						2.38%
Georgia Power [Member]
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding				868,000,000				868,000,000	868,000,000
Fixed rate pollution control revenue bonds outstanding				250,000,000				250,000,000	250,000,000
Current borrowing capacity													$ 300,000,000
Maximum borrowing capacity				1,750,000,000				1,750,000,000	1,750,000,000
Senior note issuances									650,000,000
Repayments of senior debt									700,000,000	525,000,000
Capital contributions									294,000,000	41,000,000
Remaining borrowing capacity				1,732,000,000				1,732,000,000	1,732,000,000
Georgia Power [Member] \| Senior Notes [Member] \| Series 2016A [Member]
Debt Instrument [Line Items]
Debt face amount						$ 325,000,000
Debt stated interest rate						3.25%
Georgia Power [Member] \| Senior Notes [Member] \| Series 2016B [Member]
Debt Instrument [Line Items]
Debt face amount						$ 325,000,000
Debt stated interest rate						2.40%
Georgia Power [Member] \| Unsecured Debt [Member] \| Series 2013B [Member]
Debt Instrument [Line Items]
Repayments of senior debt						$ 250,000,000
Georgia Power [Member] \| Line of Credit [Member] \| FFB Credit Facility due 2044 [Member]
Debt Instrument [Line Items]
Debt stated interest rate													2.571%	2.571%
Gulf Power [Member]
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				21,000,000				21,000,000	21,000,000
Maximum borrowing capacity				280,000,000				280,000,000	280,000,000
Senior note issuances									0
Repayments of senior debt									125,000,000	60,000,000
Remaining borrowing capacity				280,000,000				280,000,000	280,000,000
Gulf Power [Member] \| Series 2011A [Member]
Debt Instrument [Line Items]
Redemption amount of principal notes					$ 125,000,000
Gulf Power [Member] \| Senior Notes [Member] \| Series 2011A [Member]
Debt Instrument [Line Items]
Debt stated interest rate					5.75%
Gulf Power [Member] \| Bank Loans [Member]
Debt Instrument [Line Items]
Debt face amount					$ 100,000,000
Debt instrument term					11 months
Nicor Gas [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				700,000,000				700,000,000	700,000,000
Mississippi Power [Member]
Debt Instrument [Line Items]
Variable rate pollution control revenue bonds outstanding				40,000,000				40,000,000	40,000,000
Current borrowing capacity				100,000,000				100,000,000	100,000,000							$ 100,000,000
Maximum borrowing capacity				175,000,000				175,000,000	175,000,000
Senior note issuances									0
Promissory note			$ 275,000,000						0	301,000,000
Capital contributions	$ 225,000,000								227,000,000	153,000,000
Long-term debt affiliated				551,000,000				551,000,000	551,000,000								$ 576,000,000
Remaining borrowing capacity				150,000,000				150,000,000	150,000,000
Mississippi Power [Member] \| Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Debt face amount													$ 10,000,000
Mississippi Power [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Debt stated interest rate													2.35%	2.35%
Redemption amount of principal notes		$ 300,000,000
Mississippi Power [Member] \| Unsecured Debt [Member]
Debt Instrument [Line Items]
Current borrowing capacity		900,000,000
Maximum borrowing capacity		1,200,000,000.00
Remaining borrowing capacity		300,000,000
Mississippi Power [Member] \| Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Repayments of senior debt		$ 900,000,000
Traditional Operating Companies [Member]
Debt Instrument [Line Items]
Fixed rate pollution control revenue bonds outstanding				358,000,000				358,000,000	358,000,000
Southern Power [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				600,000,000				600,000,000	600,000,000
Senior note issuances									1,531,000,000
Repayments of senior debt									0	525,000,000
Capital contributions									800,000,000	$ 226,000,000
Remaining borrowing capacity				532,000,000				532,000,000	532,000,000
Southern Power [Member] \| Senior Notes [Member] \| Series 2016A [Member]
Debt Instrument [Line Items]
Debt face amount \| €														€ 600,000,000
Debt stated interest rate													1.00%	1.00%
Southern Power [Member] \| Senior Notes [Member] \| Series 2016B [Member]
Debt Instrument [Line Items]
Debt face amount \| €														€ 500,000,000
Debt stated interest rate													1.85%	1.85%
Southern Power [Member] \| Senior Notes [Member] \| Series 2016C [Member]
Debt Instrument [Line Items]
Debt face amount				$ 290,000,000				$ 290,000,000	$ 290,000,000
Debt stated interest rate				2.75%				2.75%	2.75%
Southern Power [Member] \| Bank Loans [Member]
Debt Instrument [Line Items]
Debt face amount				$ 60,000,000				$ 60,000,000	$ 60,000,000
Repayments of senior debt				80,000,000
Southern Power [Member] \| Bank Loans [Member] \| Debt Due 2016 [Member]
Debt Instrument [Line Items]
Debt face amount				400,000,000				400,000,000	400,000,000
Southern Power [Member] \| Bank Loans [Member] \| Debt Due 2018 [Member]
Debt Instrument [Line Items]
Debt face amount				320,000,000				320,000,000	320,000,000
Southern Power [Member] \| Letter of Credit [Member]
Debt Instrument [Line Items]
Debt face amount				34,000,000				34,000,000	34,000,000
Southern Power [Member] \| Project Credit Facilities [Member]
Debt Instrument [Line Items]
Current borrowing capacity				$ 828,000,000				$ 828,000,000	$ 828,000,000
Weighted average interest rate				2.05%				2.05%	2.05%
Maximum borrowing capacity				$ 828,000,000				$ 828,000,000	$ 828,000,000
Average amount outstanding				805,000,000				$ 805,000,000	805,000,000
Interest rate during period								2.02%
Southern Power [Member] \| Construction Loans [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				235,000,000				$ 235,000,000	235,000,000
Southern Power [Member] \| Henrietta [Member]
Debt Instrument [Line Items]
Construction loan												$ 217,000,000
Southern Power [Member] \| Henrietta [Member] \| Construction Loans [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				217,000,000				217,000,000	217,000,000
Average amount outstanding				137,000,000				$ 137,000,000	137,000,000
Interest rate during period								2.21%
Southern Company [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				2,250,000,000				$ 2,250,000,000	2,250,000,000
Senior note issuances					$ 8,500,000,000.0				8,500,000,000
Remaining borrowing capacity				$ 2,250,000,000				$ 2,250,000,000	$ 2,250,000,000
Southern Company [Member] \| Series 2011A [Member]
Debt Instrument [Line Items]
Debt stated interest rate				1.95%				1.95%	1.95%
Southern Company [Member] \| Senior Notes [Member] \| Senior Notes due July 1, 2018 [Member]
Debt Instrument [Line Items]
Debt face amount					$ 500,000,000
Debt stated interest rate					1.55%
Southern Company [Member] \| Senior Notes [Member] \| Senior Notes due July 1, 2019 [Member]
Debt Instrument [Line Items]
Debt face amount					$ 1,000,000,000
Debt stated interest rate					1.85%
Southern Company [Member] \| Senior Notes [Member] \| Senior Notes due July 1, 2021 [Member]
Debt Instrument [Line Items]
Debt face amount					$ 1,500,000,000.0
Debt stated interest rate					2.35%
Southern Company [Member] \| Senior Notes [Member] \| Senior Notes due July 1, 2023 [Member]
Debt Instrument [Line Items]
Debt face amount					$ 1,250,000,000.00
Debt stated interest rate					2.95%
Southern Company [Member] \| Senior Notes [Member] \| Senior Notes due July 1, 2026 [Member]
Debt Instrument [Line Items]
Debt face amount					$ 1,750,000,000.00
Debt stated interest rate					3.25%
Southern Company [Member] \| Senior Notes [Member] \| Senior Notes due July 1, 2036 [Member]
Debt Instrument [Line Items]
Debt face amount					$ 500,000,000
Debt stated interest rate					4.25%
Southern Company [Member] \| Senior Notes [Member] \| Senior Notes due July 1, 2046 [Member]
Debt Instrument [Line Items]
Debt face amount					$ 2,000,000,000
Debt stated interest rate					4.40%
Southern Company [Member] \| Junior Subordinated Debt [Member] \| Senior Notes Due 2076 [Member]
Debt Instrument [Line Items]
Debt face amount				$ 800,000,000				$ 800,000,000	$ 800,000,000
Debt stated interest rate				5.25%				5.25%	5.25%
Southern Company [Member] \| Unsecured Debt [Member] \| Series 2011A [Member]
Debt Instrument [Line Items]
Repayments of senior debt				$ 500,000,000
Southern Power's Subsidiary(ies) [Member]
Debt Instrument [Line Items]
Proceeds from long-term lines of credit									$ 691,000,000
Southern Power's Subsidiary(ies) [Member] \| Line of Credit [Member]
Debt Instrument [Line Items]
Weighted average interest rate				2.05%				2.05%	2.05%
Southern Power's Subsidiary(ies) [Member] \| Letter of Credit [Member]
Debt Instrument [Line Items]
Debt face amount				$ 16,000,000				$ 16,000,000	$ 16,000,000
Southern Company Gas [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				2,000,000,000				2,000,000,000	2,000,000,000
Senior note issuances									900,000,000
Repayments of senior debt				120,000,000
Promissory note				360,000,000
Remaining borrowing capacity				1,947,000,000				1,947,000,000	1,947,000,000
Southern Company Gas [Member] \| Senior Notes [Member] \| Senior Notes due July 1, 2023 [Member]
Debt Instrument [Line Items]
Debt face amount				$ 350,000,000				$ 350,000,000	$ 350,000,000
Debt stated interest rate				2.45%				2.45%	2.45%
Southern Company Gas [Member] \| Senior Notes [Member] \| Senior Notes due July 1, 2046 [Member]
Debt Instrument [Line Items]
Debt face amount				$ 550,000,000				$ 550,000,000	$ 550,000,000
Debt stated interest rate				3.95%				3.95%	3.95%