Financing - Narrative (Details) $ / shares in Units, shares in Thousands				1 Months Ended					3 Months Ended	9 Months Ended
	Nov. 05, 2015 USD ($)	Jul. 15, 2015 USD ($)	Jun. 03, 2015 USD ($)	Sep. 30, 2015 USD ($)	Aug. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	May. 31, 2015 USD ($) $ / shares shares	Apr. 30, 2015 USD ($) loan	Sep. 30, 2015 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Mar. 31, 2015 USD ($)
Debt Instrument [Line Items]
Amount of Variable Rate Pollution Control Revenue Bonds Outstanding Requiring Liquidity Support				$ 1,800,000,000					$ 1,800,000,000	$ 1,800,000,000
Ratio of Indebtedness to Capitalization Covenant				70.00%	65.00%				70.00%	70.00%
Line Of Credit Expire Year Four				$ 1,500,000,000					$ 1,500,000,000	$ 1,500,000,000
Line of Credit Facility, Maximum Borrowing Capacity				6,520,000,000					6,520,000,000	6,520,000,000
Line of Credit Expire Year One				35,000,000					35,000,000	35,000,000
Derivative, Notional Amount				2,065,000,000					2,065,000,000	2,065,000,000
Revenue Bond Issuances and Reofferings of Purchased Bonds										367,000,000
Scenario, Plan [Member]
Debt Instrument [Line Items]
Expected Equity Issuance				1,000,000,000					1,000,000,000	1,000,000,000
Scenario, Plan [Member] | Bridge Agreement [Member]
Debt Instrument [Line Items]
Expected Debt Issuance				7,000,000,000					7,000,000,000	7,000,000,000
Expected Equity Issuance				2,000,000,000					2,000,000,000	2,000,000,000
Line of Credit Facility, Maximum Borrowing Capacity				8,100,000,000.0					$ 8,100,000,000.0	8,100,000,000.0
Period After Funding That Loan Will Mature And Be Payable in Full									364 days
Alabama Power [Member]
Debt Instrument [Line Items]
Amount of Variable Rate Pollution Control Revenue Bonds Outstanding Requiring Liquidity Support				810,000,000					$ 810,000,000	810,000,000
Amount of Fixed Rate Pollution Control Revenue Bonds Outstanding Requiring Liquidity Support				200,000,000					200,000,000	200,000,000
Line Of Credit Expire Year Four				500,000,000					500,000,000	$ 500,000,000
Debt Instrument, Term										3 years
Line of Credit Facility, Maximum Borrowing Capacity				1,340,000,000					1,340,000,000	$ 1,340,000,000
Line of Credit Expire Year One				0					0	0
Revenue Bond Issuances and Reofferings of Purchased Bonds										80,000,000
Repayments of Senior Debt										250,000,000	$ 0
Alabama Power [Member] | 5.20% Class A Preferred Stock [Member]
Debt Instrument [Line Items]
Temporary Equity, Shares Outstanding | shares							6,480
Temporary Equity, Dividend Rate Percentage							0.052
Redemption price (in dollars per share) | $ / shares							$ 25
Alabama Power [Member] | 5.30% Class A Preferred Stock [Member]
Debt Instrument [Line Items]
Temporary Equity, Shares Outstanding | shares							4,000
Temporary Equity, Dividend Rate Percentage							0.053
Redemption price (in dollars per share) | $ / shares							$ 25
Alabama Power [Member] | 5.625% Series Preference Stock [Member]
Debt Instrument [Line Items]
Temporary Equity, Shares Outstanding | shares							6,000
Temporary Equity, Dividend Rate Percentage							0.05625
Redemption price (in dollars per share) | $ / shares							$ 25
Alabama Power [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Remarketed Pollution Control Bonds	$ 120,000,000
Alabama Power [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Redemption Amount Of Principal Notes												$ 250,000,000
Alabama Power [Member] | Series 2015A [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount								$ 175,000,000				$ 550,000,000
Debt Instrument, Interest Rate, Stated Percentage								3.75%				3.75%
Alabama Power [Member] | Series DD [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage												5.65%
Alabama Power [Member] | Series 2007B [Member]
Debt Instrument [Line Items]
Remarketing Revenue Bond								$ 80,000,000
Alabama Power [Member] | Series 2015B [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount								$ 250,000,000
Debt Instrument, Interest Rate, Stated Percentage								2.80%
Alabama Power [Member] | Aggregate Stated Capital [Member] | 5.20% Class A Preferred Stock [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount							$ 162,000,000
Alabama Power [Member] | Aggregate Stated Capital [Member] | 5.30% Class A Preferred Stock [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount							100,000,000
Alabama Power [Member] | Aggregate Stated Capital [Member] | 5.625% Series Preference Stock [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount							150,000,000
Georgia Power [Member]
Debt Instrument [Line Items]
Amount of Variable Rate Pollution Control Revenue Bonds Outstanding Requiring Liquidity Support				872,000,000					872,000,000	872,000,000
Amount of Fixed Rate Pollution Control Revenue Bonds Outstanding Requiring Liquidity Support				121,000,000					121,000,000	121,000,000
Line of Credit Facility, Increase (Decrease), Net					$ 150,000,000
Line Of Credit Expire Year Three Terminated					150,000,000
Line Of Credit Expire Year Four				0					0	0
Line of Credit Facility, Maximum Borrowing Capacity				1,750,000,000					1,750,000,000	1,750,000,000
Line of Credit Expire Year One				0					0	0
Line of Credit Facility, Current Borrowing Capacity						$ 600,000,000
Period Of Amortization Of Gain (Loss) On Settlement Of Derivatives						10 years
Revenue Bond Issuances and Reofferings of Purchased Bonds										274,000,000
Repayments of Senior Debt										525,000,000	0
Georgia Power [Member] | Interest Rate Swap [Member]
Debt Instrument [Line Items]
Gain (Loss) on Settlement Of Derivatives						$ (6,000,000)
Georgia Power [Member] | Interest Rate Swap [Member] | Cash Flow Hedges Of Forecasted Debt [Member] | Maturity Date May 2025 [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount						$ 350,000,000
Georgia Power [Member] | Second Series 2008 [Member]
Debt Instrument [Line Items]
Long-term Pollution Control Bond								$ 65,000,000
Georgia Power [Member] | Debt Held Since 2013 [Member]
Debt Instrument [Line Items]
Remarketing Revenue Bond							104,600,000
Revenue Bond Issuances and Reofferings of Purchased Bonds					10,000,000					104,600,000
Georgia Power [Member] | Debt Due 2044 [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						3.283%
Georgia Power [Member] | Debt Held Since 2009 [Member]
Debt Instrument [Line Items]
Revenue Bond Issuances and Reofferings of Purchased Bonds					94,600,000
Gulf Power [Member]
Debt Instrument [Line Items]
Amount of Variable Rate Pollution Control Revenue Bonds Outstanding Requiring Liquidity Support				82,000,000					82,000,000	82,000,000
Amount of Fixed Rate Pollution Control Revenue Bonds Outstanding Requiring Liquidity Support				33,000,000					33,000,000	33,000,000
Line Of Credit Expire Year Four				0					0	0
Line of Credit Facility, Maximum Borrowing Capacity				275,000,000					275,000,000	275,000,000
Line of Credit Expire Year One				20,000,000					20,000,000	20,000,000
Revenue Bond Issuances and Reofferings of Purchased Bonds										13,000,000
Repayments of Senior Debt										60,000,000	0
Mississippi Power [Member]
Debt Instrument [Line Items]
Amount of Variable Rate Pollution Control Revenue Bonds Outstanding Requiring Liquidity Support				40,000,000					40,000,000	40,000,000
Line Of Credit Expire Year Four				0					0	0
Line of Credit Facility, Maximum Borrowing Capacity				235,000,000					235,000,000	235,000,000
Line of Credit Expire Year One				15,000,000					15,000,000	15,000,000
Aggregate Principal Amount Of Floating Rate Bank Loan								$ 475,000,000
Bank Loans Period Of Extension			18 months			18 months
Revenue Bond Issuances and Reofferings of Purchased Bonds										0
Number Of Floating Rate Bank Loans | loan								3
Repayment Aggregate Principal Amount Of Floating Rate Bank Loan								$ 275,000,000
Promissory Note			$ 301,000,000			$ 301,000,000				301,000,000	0
Mississippi Power [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Line of Credit Expire Year One	15,000,000
Mississippi Power [Member] | Debt Due 2016 [Member]
Debt Instrument [Line Items]
Aggregate Principal Amount Of Floating Rate Bank Loan								$ 425,000,000
Number Of Floating Rate Bank Loans | loan								2
Traditional Operating Companies [Member]
Debt Instrument [Line Items]
Amount of Fixed Rate Pollution Control Revenue Bonds Outstanding Requiring Liquidity Support				354,000,000					354,000,000	354,000,000
Southern Company [Member]
Debt Instrument [Line Items]
Expires, 2020				1,250,000,000.00					1,250,000,000.00	1,250,000,000.00
Line Of Credit Expire Year Five				1,000,000,000.0	1,000,000,000.0				1,000,000,000.0	1,000,000,000.0
Line Of Credit Expire Year Four				1,000,000,000					1,000,000,000	1,000,000,000
Line of Credit Facility, Maximum Borrowing Capacity				2,250,000,000					2,250,000,000	2,250,000,000
Line of Credit Expire Year One				0					0	0
Aggregate Principal Amount Of Floating Rate Bank Loan				$ 400,000,000					400,000,000	400,000,000
Bank Loans Period Of Extension				18 months
Revenue Bond Issuances and Reofferings of Purchased Bonds										0
Southern Company [Member] | Series 2015A [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount						$ 600,000,000
Debt Instrument, Interest Rate, Stated Percentage						2.75%
Southern Company [Member] | Series 2015A [Member] | Junior Subordinated Debt [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 1,000,000,000
Debt Instrument, Interest Rate, Stated Percentage	6.25%
Southern Power [Member]
Debt Instrument [Line Items]
Expires, 2020				$ 600,000,000					600,000,000	600,000,000
Line Of Credit Expire Year Five					500,000,000
Line Of Credit Expire Year Four				0					0	0
Line of Credit Facility, Maximum Borrowing Capacity				600,000,000					600,000,000	600,000,000
Line of Credit Expire Year One				$ 0					$ 0	0
Aggregate Principal Amount Of Floating Rate Bank Loan					$ 400,000,000
Bank Loans Period Of Extension					13 months
Revenue Bond Issuances and Reofferings of Purchased Bonds										0
Repayments of Senior Debt										525,000,000	$ 0
Early Repayment of Senior Debt										$ 2,600,000
Southern Power [Member] | Series 2015A [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount							$ 350,000,000
Debt Instrument, Interest Rate, Stated Percentage							1.50%
Southern Power [Member] | Series 2015B [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount							$ 300,000,000
Debt Instrument, Interest Rate, Stated Percentage							2.375%
Southern Power [Member] | Series 2003 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.875%
Repayments of Senior Debt		$ 525,000,000