Derivatives - Energy-Related, Interest Rate, and Foreign Currency Derivatives Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) MMBTU	Dec. 31, 2014 USD ($)
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 29,000	$ 21,000
Derivative Liability, Fair Value, Gross Liability	250,000	225,000
Interest rate derivative contracts
Notional Amount	4,407,000
Fair Value Gain (Loss)	(8,000)
Alabama Power [Member]
Derivative [Line Items]
Estimated pre-tax losses that will be reclassified from OCI to interest expense for the next 12-month period	4,000
Derivative Asset, Fair Value, Gross Asset	1,000	1,000
Derivative Liability, Fair Value, Gross Liability	$ 70,000	61,000
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	50,000,000
Longest Hedge Date	2018
Gulf Power [Member]
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	82,000,000
Longest Hedge Date	2020
Southern Power [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 7,000	5,000
Derivative Liability, Fair Value, Gross Liability	3,000	4,000
Interest rate derivative contracts
Notional Amount	177,000
Fair Value Gain (Loss)	3,000
Georgia Power [Member]
Derivative [Line Items]
Estimated pre-tax losses that will be reclassified from OCI to interest expense for the next 12-month period	4,000
Interest rate derivative contracts
Notional Amount	1,400,000
Fair Value Gain (Loss)	0
Mississippi Power [Member]
Derivative [Line Items]
Estimated pre-tax losses that will be reclassified from OCI to interest expense for the next 12-month period	$ 1,000
Energy-related derivative contracts
Net Purchased mmBtu | MMBTU	32,000,000
Longest Hedge Date	2018
Maturity Date March 2016 [Member] | Cash Flow Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 250,000
Derivative Interest Rate Received	3-month LIBOR + 0.32%
Interest rate	0.75%
Derivative, basis spread on variable interest rate	0.32%
Derivative, Maturity Date	Mar. 15, 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
Derivative Interest Rate Received	3-month LIBOR + 0.32%
Interest rate	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
Derivative, basis spread on variable interest rate	0.32%
Maturity Date August 2016 [Member] | Cash Flow Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 200,000
Derivative Interest Rate Received	3-month LIBOR + 0.40%
Interest rate	1.01%
Derivative, basis spread on variable interest rate	0.40%
Derivative, Maturity Date	Aug. 15, 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
Derivative Interest Rate Received	3-month LIBOR + 0.40%
Interest rate	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
Derivative, basis spread on variable interest rate	0.40%
Maturity Date November 2026 [Member] | Cash Flow Hedges Of Forecasted Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 1,000,000
Derivative Interest Rate Received	3-month LIBOR
Interest rate	2.37%
Derivative, Maturity Date	Nov. 30, 2026
Fair Value Gain (Loss)	$ 1,000
Maturity Date November 2046 [Member] | Cash Flow Hedges Of Forecasted Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 1,000,000
Derivative Interest Rate Received	3-month LIBOR
Interest rate	2.70%
Derivative, Maturity Date	Nov. 30, 2046
Fair Value Gain (Loss)	$ (1,000)
Maturity Date October 2025 [Member] | Cash Flow Hedges Of Forecasted Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 200,000
Derivative Interest Rate Received	3-month LIBOR
Interest rate	2.93%
Derivative, Maturity Date	Oct. 15, 2025
Fair Value Gain (Loss)	$ (15,000)
Maturity Date October 2025 [Member] | Alabama Power [Member] | Cash Flow Hedges Of Forecasted Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 200,000
Derivative Interest Rate Received	3-month  LIBOR
Interest rate	2.93%
Derivative, Maturity Date	Oct. 01, 2025
Fair Value Gain (Loss)	$ (15,000)
Maturity Date November 2025 [Member] | Cash Flow Hedges Of Forecasted Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 80,000
Derivative Interest Rate Received	3-month LIBOR
Interest rate	2.32%
Derivative, Maturity Date	Dec. 15, 2026
Fair Value Gain (Loss)	$ 1,000
Maturity Date October 2025 [Member] | Gulf Power [Member] | Cash Flow Hedges Of Forecasted Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 80,000
Derivative Interest Rate Received	3-month LIBOR
Interest rate	2.32%
Derivative, Maturity Date	Dec. 01, 2026
Fair Value Gain (Loss)	$ 1,000
Maturity Date June 2018 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 250,000
Derivative Interest Rate Received	3-month LIBOR + 4.02%
Interest rate	5.40%
Derivative, basis spread on variable interest rate	4.02%
Derivative, Maturity Date	Jun. 01, 2018
Fair Value Gain (Loss)	$ 1,000
Maturity Date June 2018 [Member] | Georgia Power [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 250,000
Derivative Interest Rate Received	3-month LIBOR + 4.02%
Interest rate	5.40%
Derivative, basis spread on variable interest rate	4.02%
Derivative, Maturity Date	Jun. 01, 2018
Fair Value Gain (Loss)	$ 1,000
Maturity Date December 2019 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 200,000
Derivative Interest Rate Received	3-month LIBOR + 2.46%
Interest rate	4.25%
Derivative, basis spread on variable interest rate	2.46%
Derivative, Maturity Date	Dec. 01, 2019
Fair Value Gain (Loss)	$ 2,000
Maturity Date December 2019 [Member] | Georgia Power [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 200,000
Derivative Interest Rate Received	3-month LIBOR + 2.46%
Interest rate	4.25%
Derivative, basis spread on variable interest rate	2.46%
Derivative, Maturity Date	Dec. 01, 2019
Fair Value Gain (Loss)	$ 2,000
Maturity Date August 2017 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 250,000
Derivative Interest Rate Received	3-month LIBOR + 0.17%
Interest rate	1.30%
Derivative, basis spread on variable interest rate	0.17%
Derivative, Maturity Date	Aug. 15, 2017
Fair Value Gain (Loss)	$ 1,000
Maturity Date June 2020 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 300,000
Derivative Interest Rate Received	3-month LIBOR + 0.92%
Interest rate	2.75%
Derivative, basis spread on variable interest rate	0.92%
Derivative, Maturity Date	Jun. 15, 2020
Fair Value Gain (Loss)	$ 2,000
Maturity Date December 2018 [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 500,000
Derivative Interest Rate Received	3-month LIBOR + 0.76%
Interest rate	1.95%
Derivative, basis spread on variable interest rate	0.76%
Derivative, Maturity Date	Dec. 01, 2018
Fair Value Gain (Loss)	$ (3,000)
Maturity Date December 2018 [Member] | Georgia Power [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Notional Amount	$ 500,000
Derivative Interest Rate Received	3-month LIBOR + .76%
Interest rate	1.95%
Derivative, basis spread on variable interest rate	0.76%
Derivative, Maturity Date	Dec. 01, 2018
Fair Value Gain (Loss)	$ (3,000)
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	4,000	6,000
Derivative Liability, Fair Value, Gross Liability	1,000	4,000
Not Designated as Hedging Instrument [Member] | Gulf Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,000	0
Derivative Liability, Fair Value, Gross Liability	100,000	72,000
Not Designated as Hedging Instrument [Member] | Southern Power [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	4,000	5,000
Derivative Liability, Fair Value, Gross Liability	$ 1,000	4,000
Not Designated as Hedging Instrument [Member] | Maturity Date October 2016 [Member] | Southern Power [Member]
Derivative [Line Items]
Derivative, Term of Contract	15 years
Not Designated as Hedging Instrument [Member] | Maturity Date November 2016 [Member] | Southern Power [Member]
Derivative [Line Items]
Derivative, Term of Contract	12 years
Other Current Assets [Member] | Not Designated as Hedging Instrument [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 1,000	6,000
Other Current Assets [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	3,000	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	1,000	4,000
Liabilities from risk management activities [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	0	0
Other deferred charges and assets [Member] | Not Designated as Hedging Instrument [Member] | Southern Power [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	0	$ 0
RE Tranquility Holdings, LLC [Member] | Not Designated as Hedging Instrument [Member] | Maturity Date October 2016 [Member] | Southern Power [Member]
Interest rate derivative contracts
Notional Amount	$ 65,000
Derivative Interest Rate Received	3-month LIBOR
Interest rate	2.50%
Derivative, Maturity Date	Oct. 31, 2016
Fair Value Gain (Loss)	$ 1,000
RE Roserock Holdings, LLC [Member] | Not Designated as Hedging Instrument [Member] | Maturity Date October 2016 [Member] | Southern Power [Member]
Interest rate derivative contracts
Notional Amount	$ 47,000
Derivative Interest Rate Received	3-month LIBOR
Interest rate	2.21%
Fair Value Gain (Loss)	$ 1,000
RE Garland Holdings, LLC [Member] | Maturity Date November 2016 [Member] | Southern Power [Member] | Fair Value Hedges Of Existing Debt [Member]
Interest rate derivative contracts
Derivative, Maturity Date	Nov. 22, 2016
RE Garland Holdings, LLC [Member] | Not Designated as Hedging Instrument [Member] | Maturity Date November 2016 [Member] | Southern Power [Member]
Interest rate derivative contracts
Notional Amount	$ 65,000
Derivative Interest Rate Received	3-month LIBOR
Interest rate	2.21%
Fair Value Gain (Loss)	$ 1,000