Derivatives - Pre-tax Effect of Derivatives on Balance Sheets and Statements of Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Loss	$ (197,000)	$ (55,000)
Regulatory Hedge Unrealized Gain	7,000	23,000
Other regulatory assets current [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Loss	(118,000)	(26,000)
Other regulatory assets deferred [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Loss	(79,000)	(29,000)
Other regulatory liabilities current [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain	7,000	16,000
Other regulatory liabilities deferred [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain	0	7,000
Alabama Power [Member] | Interest expense, net of amounts capitalized [Member]
Pre-tax effect of derivatives designated as cash flow hedging instruments
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(3,000)	(3,000)	(3,000)
Alabama Power [Member] | Interest rate derivatives [Member]
Pre-tax effect of derivatives designated as cash flow hedging instruments
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(8,000)	0	(18,000)
Alabama Power [Member] | Other regulatory assets current [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Loss	(32,000)	(3,000)
Alabama Power [Member] | Other regulatory assets deferred [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Loss	(21,000)	(5,000)
Alabama Power [Member] | Other regulatory assets [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Loss	(53,000)	(8,000)
Alabama Power [Member] | Other Current Liabilities [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain	1,000	5,000
Alabama Power [Member] | Other regulatory liabilities deferred [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain	0	2,000
Alabama Power [Member] | Other regulatory liabilities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain	1,000	7,000
Georgia Power [Member] | Other regulatory assets current [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Loss	(23,000)	(13,000)
Georgia Power [Member] | Other regulatory assets deferred [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Loss	(4,000)	(8,000)
Georgia Power [Member] | Other regulatory assets [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Loss	(27,000)	(21,000)
Georgia Power [Member] | Other regulatory liabilities current [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain	6,000	3,000
Georgia Power [Member] | Other deferred credits and liabilities [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain	1,000	2,000
Georgia Power [Member] | Other regulatory liabilities [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain	7,000	5,000
Gulf Power [Member] | Interest rate derivatives [Member]
Pre-tax effect of derivatives designated as cash flow hedging instruments
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	0	0	0
Gulf Power [Member] | Interest rate derivatives [Member] | Interest expense, net of amounts capitalized [Member]
Pre-tax effect of derivatives designated as cash flow hedging instruments
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(606)	(769)	(933)
Gulf Power [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Loss	(72,424)	(17,043)
Regulatory Hedge Unrealized Gain	112	6,962
Gulf Power [Member] | Other regulatory assets current [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Loss	(36,922)	(6,470)
Gulf Power [Member] | Other regulatory assets deferred [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Loss	(35,502)	(10,573)
Gulf Power [Member] | Other regulatory liabilities current [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain	34	4,893
Gulf Power [Member] | Other regulatory liabilities deferred [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain	78	2,069
Mississippi Power [Member] | Hedging Instruments for Regulatory Purposes [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Loss	(45,418)	(10,281)
Regulatory Hedge Unrealized Gain	52	4,803
Mississippi Power [Member] | Cash Flow Hedging [Member]
Pre-tax effect of derivatives designated as cash flow hedging instruments
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	0	0	(774)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(1,375)	(1,375)	(1,073)
Mississippi Power [Member] | Cash Flow Hedging [Member] | Energy Related Derivative [Member]
Pre-tax effect of derivatives designated as cash flow hedging instruments
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	0	0	0
Mississippi Power [Member] | Cash Flow Hedging [Member] | Energy Related Derivative [Member] | Fuel [Member]
Pre-tax effect of derivatives designated as cash flow hedging instruments
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	0	0	0
Mississippi Power [Member] | Cash Flow Hedging [Member] | Interest rate derivatives [Member]
Pre-tax effect of derivatives designated as cash flow hedging instruments
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	0	0	(774)
Mississippi Power [Member] | Cash Flow Hedging [Member] | Interest rate derivatives [Member] | Interest expense, net of amounts capitalized [Member]
Pre-tax effect of derivatives designated as cash flow hedging instruments
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(1,375)	(1,375)	(1,073)
Mississippi Power [Member] | Other regulatory assets current [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Loss	(26,259)	(3,652)
Mississippi Power [Member] | Other regulatory assets deferred [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Loss	(19,159)	(6,629)
Mississippi Power [Member] | Other regulatory liabilities current [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain	30	3,352
Mississippi Power [Member] | Other regulatory liabilities deferred [Member] | Hedging Instruments for Regulatory Purposes [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain	22	1,451
Southern Power [Member]
Pre-tax effect of derivatives designated as cash flow hedging instruments
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(500)	(6,100)	(10,100)
Southern Power [Member] | Energy Related Derivative [Member] | Depreciation and amortization [Member]
Pre-tax effect of derivatives designated as cash flow hedging instruments
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	400	400	400
Southern Power [Member] | Interest rate derivatives [Member] | Interest expense, net of amounts capitalized [Member]
Pre-tax effect of derivatives designated as cash flow hedging instruments
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	$ (900)	$ (6,500)	$ (10,500)