Derivatives - Energy-Related, Interest Rate, and Foreign Currency Derivatives Information (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 MMBTU	Oct. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 21,000,000		$ 27,000,000
Derivative Liability, Fair Value, Gross Liability	225,000,000		56,000,000
Interest rate derivative contracts
Notional Amount	2,050,000,000
Fair Value Gain (Loss)	(16,000,000)
Alabama Power [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,000,000		7,000,000
Derivative Liability, Fair Value, Gross Liability	61,000,000		8,000,000
Energy-related derivative contracts
Net Purchased mmBtu	56,000,000
Longest Hedge Date	2017
Interest rate derivative contracts
Notional Amount		200,000,000
Georgia Power [Member]
Interest rate derivative contracts
Notional Amount	1,600,000,000
Fair Value Gain (Loss)	(9,000,000)
Mississippi Power [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	52,000		4,803,000
Derivative Liability, Fair Value, Gross Liability	45,418,000		10,282,000
Energy-related derivative contracts
Net Purchased mmBtu	54,000,000
Longest Hedge Date	2018
Maturity Date October 2025 [Member] | Cash Flow Hedges Of Forecasted Debt [Member]
Interest rate derivative contracts
Notional Amount	200,000,000
Derivative Interest Rate Received	3-month LIBOR
Notional Amount of Interest Rate Derivatives Interest Rate Paid	2.93%
Derivative, Maturity Date	Oct. 01, 2025
Fair Value Gain (Loss)	(8,000,000)
Maturity Date October 2025 [Member] | Alabama Power [Member] | Cash Flow Hedges Of Forecasted Debt [Member]
Interest rate derivative contracts
Notional Amount	200,000,000
Derivative Interest Rate Received	3-month  LIBOR
Notional Amount of Interest Rate Derivatives Interest Rate Paid	2.93%
Derivative, Maturity Date	Oct. 01, 2025
Fair Value Gain (Loss)	(8,000,000)
Maturity Date May 2025 [Member] | Cash Flow Hedges Of Forecasted Debt [Member]
Interest rate derivative contracts
Notional Amount	350,000,000
Derivative Interest Rate Received	3-month LIBOR
Notional Amount of Interest Rate Derivatives Interest Rate Paid	2.57%
Derivative, Maturity Date	May 01, 2025
Fair Value Gain (Loss)	(6,000,000)
Maturity Date May 2025 [Member] | Georgia Power [Member] | Cash Flow Hedges Of Forecasted Debt [Member]
Interest rate derivative contracts
Notional Amount	350,000,000
Derivative Interest Rate Received	3-month LIBOR
Notional Amount of Interest Rate Derivatives Interest Rate Paid	2.57%
Derivative, Maturity Date	May 01, 2025
Fair Value Gain (Loss)	(6,000,000)
Maturity Date March 2016 [Member] | Cash Flow Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	250,000,000
Derivative Interest Rate Received	3-month LIBOR + 0.32%
Fair Value Hedges Weighted Average Interest Rate	0.0075
Notional Amount of Interest Rate Derivatives Interest Rate Paid	0.32%
Derivative, Maturity Date	Mar. 01, 2016
Fair Value Gain (Loss)	0
Maturity Date March 2016 [Member] | Georgia Power [Member] | Cash Flow Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	250,000,000
Derivative Interest Rate Received	3-month LIBOR + 0.32%
Notional Amount of Interest Rate Derivatives Interest Rate Paid	0.75%
Derivative, Maturity Date	Mar. 01, 2016
Fair Value Gain (Loss)	0
Maturity Date March 2016 [Member] | Interest Rate Contract [Member] | Georgia Power [Member] | Cash Flow Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount of Interest Rate Derivatives Interest Rate Paid	0.32%
Maturity Date August 2016 [Member] | Cash Flow Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	200,000,000
Derivative Interest Rate Received	3-month LIBOR + 0.40%
Fair Value Hedges Weighted Average Interest Rate	0.0101
Notional Amount of Interest Rate Derivatives Interest Rate Paid	0.40%
Derivative, Maturity Date	Aug. 01, 2016
Fair Value Gain (Loss)	0
Maturity Date August 2016 [Member] | Georgia Power [Member] | Cash Flow Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	200,000,000
Derivative Interest Rate Received	3-month LIBOR + 0.40%
Notional Amount of Interest Rate Derivatives Interest Rate Paid	1.01%
Derivative, Maturity Date	Aug. 01, 2016
Fair Value Gain (Loss)	0
Maturity Date August 2016 [Member] | Interest Rate Contract [Member] | Georgia Power [Member] | Cash Flow Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount of Interest Rate Derivatives Interest Rate Paid	0.40%
Maturity Date June 2018 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	250,000,000
Derivative Interest Rate Received	3-month LIBOR + 4.02%
Derivative, Fixed Interest Rate	4.02%
Notional Amount of Interest Rate Derivatives Interest Rate Paid	5.40%
Derivative, Maturity Date	Jun. 01, 2018
Fair Value Gain (Loss)	(1,000,000)
Maturity Date June 2018 [Member] | Georgia Power [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	250,000,000
Derivative Interest Rate Received	3-month LIBOR + 4.02%
Derivative, Fixed Interest Rate	4.02%
Notional Amount of Interest Rate Derivatives Interest Rate Paid	5.40%
Derivative, Maturity Date	Jun. 01, 2018
Fair Value Gain (Loss)	(1,000,000)
Maturity Date December 2019 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	200,000,000
Derivative Interest Rate Received	3-month LIBOR + 2.46%
Derivative, Fixed Interest Rate	2.46%
Notional Amount of Interest Rate Derivatives Interest Rate Paid	4.25%
Derivative, Maturity Date	Dec. 01, 2019
Fair Value Gain (Loss)	0
Maturity Date December 2019 [Member] | Georgia Power [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	200,000,000
Derivative Interest Rate Received	3-month LIBOR + 2.46%
Derivative, Fixed Interest Rate	4.46%
Notional Amount of Interest Rate Derivatives Interest Rate Paid	4.25%
Derivative, Maturity Date	Dec. 01, 2019
Fair Value Gain (Loss)	0
Maturity Date November 2025 [Member] | Cash Flow Hedges Of Forecasted Debt [Member]
Interest rate derivative contracts
Notional Amount	350,000,000
Derivative Interest Rate Received	3-month LIBOR
Notional Amount of Interest Rate Derivatives Interest Rate Paid	2.57%
Derivative, Maturity Date	Nov. 01, 2025
Fair Value Gain (Loss)	(2,000,000)
Maturity Date November 2025 [Member] | Georgia Power [Member] | Cash Flow Hedges Of Forecasted Debt [Member]
Interest rate derivative contracts
Notional Amount	350,000,000
Derivative Interest Rate Received	3-month LIBOR
Notional Amount of Interest Rate Derivatives Interest Rate Paid	2.57%
Derivative, Maturity Date	Nov. 01, 2025
Fair Value Gain (Loss)	(2,000,000)
Maturity Date August 2017 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	250,000,000
Derivative Interest Rate Received	3-month LIBOR + 0.17%
Derivative, Fixed Interest Rate	0.17%
Notional Amount of Interest Rate Derivatives Interest Rate Paid	1.30%
Derivative, Maturity Date	Aug. 01, 2017
Fair Value Gain (Loss)	1,000,000
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	6,000,000		1,000,000
Derivative Liability, Fair Value, Gross Liability	4,000,000		1,000,000
Other Current Assets [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	6,000,000		0
Liabilities from risk management activities [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	4,000,000		1,000,000
Other deferred charges and assets [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	0		1,000,000
Other deferred credits and liabilities [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ 0		$ 0