Derivatives - Pre-tax Effects of Derivatives Designated as Cash Flow Hedging Instruments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Southern Company [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	$ 31	$ (28)	$ (191)	$ (26)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(4)	(2)	(32)	(7)
Southern Company [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	(85)		(85)		$ (214)
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	0	0	(1)	0
Southern Company [Member] | Energy Related Derivative [Member] | Amortization [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	1	0	1	0
Southern Company [Member] | Energy Related Derivative [Member] | Other regulatory assets, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	(52)		(52)		(130)
Southern Company [Member] | Energy Related Derivative [Member] | Other regulatory assets, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	(42)		(42)		(87)
Southern Company [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	8		8		3
Southern Company [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	1		1
Southern Company [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(6)	(28)	(189)	(26)
Southern Company [Member] | Interest Rate Contract [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(6)	(2)	(13)	(7)
Southern Company [Member] | Foreign Exchange Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	37	0		0
Southern Company [Member] | Foreign Exchange Contract [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(6)	0	(7)	0
Southern Company [Member] | Foreign Exchange Contract [Member] | Other Income Expense Net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	7	0	(13)	0
Alabama Power [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	(13)		(13)		(54)
Alabama Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	(10)		(10)		(40)
Alabama Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	(4)		(4)		(15)
Alabama Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	1		1		1
Alabama Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	0		0
Alabama Power [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	0	(10)	(3)	(9)
Alabama Power [Member] | Interest Rate Contract [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(2)	(1)	(5)	(2)
Georgia Power [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	(1)		(1)		(13)
Georgia Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	(2)		(2)		(12)
Georgia Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	(4)		(4)		(3)
Georgia Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	4		4		2
Georgia Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	1		1
Georgia Power [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	0	(18)	0	(17)
Georgia Power [Member] | Interest Rate Contract [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(1)	(1)	(3)	(3)
Gulf Power [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	(50)		(50)		(100)
Gulf Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	(24)		(24)		(49)
Gulf Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	(26)		(26)		(51)
Gulf Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	0		0		0
Gulf Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	0		0
Gulf Power [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)			(7)	0
Gulf Power [Member] | Interest Rate Contract [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)			0	0
Mississippi Power [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	(21)		(21)		(47)
Mississippi Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	(13)		(13)		(29)
Mississippi Power [Member] | Energy Related Derivative [Member] | Other regulatory assets, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	(8)		(8)		(18)
Mississippi Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, current [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	0		0		$ 0
Mississippi Power [Member] | Energy Related Derivative [Member] | Other regulatory liabilities, deferred [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory Hedge Unrealized Gain (Loss) Recognized on the Balance Sheet	0		0
Mississippi Power [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)			(1)	0
Mississippi Power [Member] | Interest Rate Contract [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)			(1)	(1)
Southern Power [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	37	0	(2)	0
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	2	0	(20)	(1)
Southern Power [Member] | Energy Related Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	0	0	(1)	0
Southern Power [Member] | Energy Related Derivative [Member] | Amortization [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	1	0	1	0
Southern Power [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)			0	0
Southern Power [Member] | Interest Rate Contract [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)			(1)	(1)
Southern Power [Member] | Foreign Exchange Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	37	0	(1)	0
Southern Power [Member] | Foreign Exchange Contract [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(6)	0	(7)	0
Southern Power [Member] | Foreign Exchange Contract [Member] | Other Income Expense Net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	$ 7	$ 0	$ (13)	$ 0