Derivatives - Pre-tax Effects of Derivatives Designated as Cash Flow Hedging Instruments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Collateral already posted, aggregate fair value	$ 71		$ 71
Southern Company
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	61	$ (33)	46	$ (223)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	67	(25)	68	(28)
Southern Company | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(34)		(34)		$ 33
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(9)	0	(20)	0
Southern Company | Energy-related derivatives | Depreciation and amortization
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(2)	0	(6)	0
Southern Company | Energy-related derivatives | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(24)		(24)		(16)
Southern Company | Energy-related derivatives | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(23)		(23)		(19)
Southern Company | Energy-related derivatives | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	13		13		56
Southern Company | Energy-related derivatives | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet					12
Southern Company | Interest Rate Contract
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(1)	6	(1)	(184)
Southern Company | Interest Rate Contract | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(5)	(4)	(10)	(7)
Southern Company | Foreign Exchange Contract
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	71	(39)	67	(39)
Southern Company | Foreign Exchange Contract | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(5)	(1)	(12)	(1)
Southern Company | Foreign Exchange Contract | Other income (expense), net
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	79	(20)	96	(20)
ALABAMA POWER CO | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(2)		(2)		11
ALABAMA POWER CO | Energy-related derivatives | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(3)		(3)		(1)
ALABAMA POWER CO | Energy-related derivatives | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(2)		(2)		0
ALABAMA POWER CO | Energy-related derivatives | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	3		3		8
ALABAMA POWER CO | Energy-related derivatives | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet					4
ALABAMA POWER CO | Interest Rate Contract
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	0	0	0	(4)
ALABAMA POWER CO | Interest Rate Contract | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(2)	(2)	(3)	(3)
GEORGIA POWER CO | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	1		1		36
GEORGIA POWER CO | Energy-related derivatives | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0		0
GEORGIA POWER CO | Energy-related derivatives | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(5)		(5)		0
GEORGIA POWER CO | Energy-related derivatives | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	6		6		29
GEORGIA POWER CO | Energy-related derivatives | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet					7
GEORGIA POWER CO | Interest Rate Contract
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	0	0	0	0
GEORGIA POWER CO | Interest Rate Contract | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(1)	(1)	(3)	(2)
GULF POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)			(2)	(7)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)			0	0
GULF POWER CO | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(28)		(28)		(24)
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)			(1)	0
GULF POWER CO | Energy-related derivatives | Depreciation and amortization
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)			0	0
GULF POWER CO | Energy-related derivatives | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(15)		(15)		(9)
GULF POWER CO | Energy-related derivatives | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(13)		(13)		(16)
GULF POWER CO | Energy-related derivatives | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0		1
GULF POWER CO | Energy-related derivatives | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet					0
GULF POWER CO | Interest Rate Contract
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(1)	(2)	(1)	(7)
GULF POWER CO | Interest Rate Contract | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	0	0	0	0
MISSISSIPPI POWER CO | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(8)		(8)		(7)
MISSISSIPPI POWER CO | Energy-related derivatives | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(5)		(5)		(5)
MISSISSIPPI POWER CO | Energy-related derivatives | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(3)		(3)		(3)
MISSISSIPPI POWER CO | Energy-related derivatives | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0		1
MISSISSIPPI POWER CO | Energy-related derivatives | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet					0
MISSISSIPPI POWER CO | Interest Rate Contract
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)			0	0
MISSISSIPPI POWER CO | Interest Rate Contract | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)			(1)	(1)
SOUTHERN Co GAS
Derivative Instruments, Gain (Loss) [Line Items]
Collateral already posted, aggregate fair value	71		71		62
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(2)		(4)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	0		0
SOUTHERN Co GAS | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	3		3		17
Collateral already posted, aggregate fair value	1		1		8
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(2)		(4)
SOUTHERN Co GAS | Energy-related derivatives | Cost of natural gas
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	0		0
SOUTHERN Co GAS | Energy-related derivatives | Other regulatory assets, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	(1)		(1)		(1)
SOUTHERN Co GAS | Energy-related derivatives | Other regulatory assets, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	0		0		0
SOUTHERN Co GAS | Energy-related derivatives | Other regulatory liabilities, current
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet	4		4		17
SOUTHERN Co GAS | Energy-related derivatives | Other regulatory liabilities, deferred
Derivative Instruments, Gain (Loss) [Line Items]
Regulatory hedge unrealized gain (loss) recognized on the balance sheet					$ 1
SOUTHERN Co GAS | Interest Rate Contract
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	0		0
SOUTHERN Co GAS | Interest Rate Contract | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	0		0
SOUTHERN POWER CO
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	64	(39)	52	(39)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	72	(21)	78	(22)
SOUTHERN POWER CO | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(7)	0	(15)	0
SOUTHERN POWER CO | Energy-related derivatives | Depreciation and amortization
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(2)	0	(6)	0
SOUTHERN POWER CO | Interest Rate Contract
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)			0	0
SOUTHERN POWER CO | Interest Rate Contract | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)			0	(1)
SOUTHERN POWER CO | Foreign Exchange Contract
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	71	(39)	67	(39)
SOUTHERN POWER CO | Foreign Exchange Contract | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(5)	(1)	(12)	(1)
SOUTHERN POWER CO | Foreign Exchange Contract | Other income (expense), net
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	$ 79	(20)	$ 96	(20)
Predecessor | SOUTHERN Co GAS
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)		(19)		(64)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)		(2)		(1)
Predecessor | SOUTHERN Co GAS | Energy-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)		0		0
Predecessor | SOUTHERN Co GAS | Energy-related derivatives | Cost of natural gas
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)		(1)		(1)
Predecessor | SOUTHERN Co GAS | Interest Rate Contract
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)		(19)		(64)
Predecessor | SOUTHERN Co GAS | Interest Rate Contract | Interest expense, net of amounts capitalized
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)		$ (1)		$ 0