Derivatives - Financial Statement Presentation (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Loss	$ 217,000	$ 197,000
Regulatory Hedge Unrealized Gain	3,000	7,000
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	29,000	21,000
Liability Derivatives	250,000	225,000
Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	4,000	6,000
Liability Derivatives	1,000	4,000
Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	7,000	13,000
Liability Derivatives	220,000	201,000
Energy Related Derivative [Member] | Other regulatory assets current [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Loss	130,000	118,000
Energy Related Derivative [Member] | Other current assets [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	1,000	6,000
Energy Related Derivative [Member] | Liabilities from risk management activities [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	1,000	4,000
Energy Related Derivative [Member] | Other regulatory liabilities current [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Gain	3,000	7,000
Energy Related Derivative [Member] | Other regulatory assets deferred [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Loss	87,000	79,000
Energy Related Derivative [Member] | Other regulatory liabilities deferred [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Gain	0	0
Energy Related Derivative [Member] | Gross Amount Of Derivatives [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(6,000)	(9,000)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(6,000)	(9,000)
Interest rate derivatives [Member] | Net Amount Of Derivatives [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	22,000	8,000
Liability Derivatives	30,000	24,000
Interest rate derivatives [Member] | Other current assets [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	3,000	0
Interest rate derivatives [Member] | Liabilities from risk management activities [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	0	0
Interest rate derivatives [Member] | Gross Amount Of Derivatives [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(9,000)	(8,000)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(9,000)	(8,000)
Georgia Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	2,000	7,000
Liability Derivatives	15,000	27,000
Georgia Power [Member] | Energy Related Derivative [Member] | Gross Amount Of Derivatives [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(2,000)	(7,000)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(2,000)	(7,000)
Georgia Power [Member] | Interest rate derivatives [Member] | Net Amount Of Derivatives [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	5,000	6,000
Liability Derivatives	6,000	14,000
Georgia Power [Member] | Interest rate derivatives [Member] | Gross Amount Of Derivatives [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(4,000)	(6,000)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(4,000)	(6,000)
Alabama Power [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	1,000	1,000
Liability Derivatives	70,000	61,000
Alabama Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	1,000	1,000
Liability Derivatives	55,000	53,000
Alabama Power [Member] | Energy Related Derivative [Member] | Other regulatory assets current [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Loss	40,000	32,000
Alabama Power [Member] | Energy Related Derivative [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Gain	1,000	1,000
Alabama Power [Member] | Energy Related Derivative [Member] | Other regulatory assets deferred [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Loss	15,000	21,000
Alabama Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities deferred [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Gain	0	0
Alabama Power [Member] | Energy Related Derivative [Member] | Gross Amount Of Derivatives [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(1,000)	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(1,000)	0
Gulf Power [Member] | Energy Related Derivative [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	1,000	0
Liability Derivatives	100,000	72,000
Southern Power [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	7,000	5,000
Liability Derivatives	3,000	4,000
Southern Power [Member] | Energy Related Derivative [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	4,000	5,000
Liability Derivatives	1,000	4,000
Southern Power [Member] | Energy Related Derivative [Member] | Net Amount Of Derivatives [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	4,000	5,000
Liability Derivatives	3,000	4,000
Southern Power [Member] | Energy Related Derivative [Member] | Assets from risk management activities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	3,000	0
Southern Power [Member] | Energy Related Derivative [Member] | Assets from risk management activities [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	1,000	5,000
Southern Power [Member] | Energy Related Derivative [Member] | Other Current Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	2,000	0
Southern Power [Member] | Energy Related Derivative [Member] | Other Current Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	1,000	4,000
Southern Power [Member] | Energy Related Derivative [Member] | Gross Amount Of Derivatives [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(1,000)	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(1,000)	0
Southern Power [Member] | Interest rate derivatives [Member] | Other deferred charges and assets [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	0	0
Southern Power [Member] | Interest rate derivatives [Member] | Assets from risk management activities [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	3,000	0
Hedging Instruments for Regulatory Purposes [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	3,000	7,000
Liability Derivatives	217,000	197,000
Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	3,000	7,000
Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	130,000	118,000
Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	0	0
Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	87,000	79,000
Hedging Instruments for Regulatory Purposes [Member] | Mississippi Power [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Loss	47,000	45,000
Regulatory Hedge Unrealized Gain	0	0
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	0	0
Liability Derivatives	47,000	45,000
Hedging Instruments for Regulatory Purposes [Member] | Mississippi Power [Member] | Energy Related Derivative [Member] | Other regulatory assets current [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Loss	29,000	26,000
Hedging Instruments for Regulatory Purposes [Member] | Mississippi Power [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	0	0
Hedging Instruments for Regulatory Purposes [Member] | Mississippi Power [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	29,000	26,000
Hedging Instruments for Regulatory Purposes [Member] | Mississippi Power [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	0	0
Hedging Instruments for Regulatory Purposes [Member] | Mississippi Power [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	18,000	19,000
Hedging Instruments for Regulatory Purposes [Member] | Mississippi Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities current [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Gain	0	0
Hedging Instruments for Regulatory Purposes [Member] | Mississippi Power [Member] | Energy Related Derivative [Member] | Other regulatory assets deferred [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Loss	18,000	19,000
Hedging Instruments for Regulatory Purposes [Member] | Mississippi Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities deferred [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Gain	0	0
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	7,000	13,000
Liability Derivatives	21,000	41,000
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Energy Related Derivative [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	2,000	7,000
Liability Derivatives	15,000	27,000
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Energy Related Derivative [Member] | Other regulatory assets current [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Loss	12,000	23,000
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	2,000	6,000
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	12,000	23,000
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	0	1,000
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Gain	0	1,000
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	3,000	4,000
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities current [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Gain	2,000	6,000
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Energy Related Derivative [Member] | Other regulatory assets deferred [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Loss	3,000	4,000
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Interest rate derivatives [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	5,000	6,000
Liability Derivatives	6,000	14,000
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Interest rate derivatives [Member] | Other current assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	5,000	5,000
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Interest rate derivatives [Member] | Liabilities from risk management activities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	0	9,000
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Interest rate derivatives [Member] | Other deferred charges and assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	0	1,000
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Interest rate derivatives [Member] | Other deferred credits and liabilities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	6,000	5,000
Hedging Instruments for Regulatory Purposes [Member] | Alabama Power [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	1,000	1,000
Liability Derivatives	55,000	53,000
Hedging Instruments for Regulatory Purposes [Member] | Alabama Power [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	1,000	1,000
Hedging Instruments for Regulatory Purposes [Member] | Alabama Power [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	40,000	32,000
Hedging Instruments for Regulatory Purposes [Member] | Alabama Power [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	0	0
Hedging Instruments for Regulatory Purposes [Member] | Alabama Power [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	15,000	21,000
Hedging Instruments for Regulatory Purposes [Member] | Alabama Power [Member] | Interest rate derivatives [Member] | Other current assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	0	0
Hedging Instruments for Regulatory Purposes [Member] | Alabama Power [Member] | Interest rate derivatives [Member] | Liabilities from risk management activities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	15,000	8,000
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Energy Related Derivative [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Loss	100,000	72,000
Regulatory Hedge Unrealized Gain	0	0
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	0	0
Liability Derivatives	100,000	72,000
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Energy Related Derivative [Member] | Other regulatory assets current [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Loss	49,000	37,000
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	0	0
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	49,000	37,000
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Energy Related Derivative [Member] | Other deferred charges and assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	0	0
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Energy Related Derivative [Member] | Other deferred credits and liabilities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	51,000	35,000
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities current [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Gain	0	0
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Energy Related Derivative [Member] | Other regulatory assets deferred [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Loss	51,000	35,000
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities deferred [Member]
Derivatives, Fair Value [Line Items]
Regulatory Hedge Unrealized Gain	0	0
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Interest rate derivatives [Member] | Other current assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	1,000	0
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Interest rate derivatives [Member] | Liabilities from risk management activities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	0	0
Cash Flow and Fair Value Hedging [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	22,000	8,000
Liability Derivatives	32,000	24,000
Cash Flow and Fair Value Hedging [Member] | Energy Related Derivative [Member] | Other current assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	3,000	0
Cash Flow and Fair Value Hedging [Member] | Energy Related Derivative [Member] | Liabilities from risk management activities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	2,000	0
Cash Flow and Fair Value Hedging [Member] | Interest rate derivatives [Member] | Other current assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	19,000	7,000
Cash Flow and Fair Value Hedging [Member] | Interest rate derivatives [Member] | Liabilities from risk management activities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	23,000	17,000
Cash Flow and Fair Value Hedging [Member] | Interest rate derivatives [Member] | Other deferred charges and assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Asset Derivatives	0	1,000
Cash Flow and Fair Value Hedging [Member] | Interest rate derivatives [Member] | Other deferred credits and liabilities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Liability Derivatives	$ 7,000	$ 7,000