Derivatives - Financial Statement Presentation (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair value of energy-related derivatives and interest rate derivatives
Collateral already posted, aggregate fair value	$ 62
Energy-related derivatives
Fair value of energy-related derivatives and interest rate derivatives
Collateral already posted, aggregate fair value	8
Parent Company [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	690	$ 29
Derivative asset, gross amount offset	(462)	(15)
Derivative Asset	228	14
Derivative liability, gross	718	250
Derivative liability, gross amounts offset	(524)	(15)
Derivative Liability	194	235
Parent Company [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	556	4
Derivative liability, gross	564	1
Parent Company [Member] | Energy-related derivatives | Other current assets [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	489	1
Parent Company [Member] | Energy-related derivatives | Liabilities from risk management activities, net of collateral [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	483	1
Parent Company [Member] | Energy-related derivatives | Other deferred charges and assets [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	66	0
Parent Company [Member] | Energy-related derivatives | Other deferred credits and liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	81	0
Parent Company [Member] | Interest rate derivatives | Other current assets [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	1	3
Alabama Power [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	20	1
Derivative asset, gross amount offset	(8)	(1)
Derivative Asset	12	0
Derivative liability, gross	9	70
Derivative liability, gross amounts offset	(8)	(1)
Derivative Liability	1	69
Georgia Power [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	46	7
Derivative asset, gross amount offset	(8)	(6)
Derivative Asset	38	1
Derivative liability, gross	11	21
Derivative liability, gross amounts offset	(8)	(6)
Derivative Liability	3	15
Gulf Power [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	5	1
Derivative asset, gross amount offset	(4)	0
Derivative Asset	1	1
Derivative liability, gross	29	100
Derivative liability, gross amounts offset	(4)	0
Derivative Liability	25	100
Mississippi Power [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	7	0
Derivative asset, gross amount offset	(3)	0
Derivative Asset	4	0
Derivative liability, gross	11	47
Derivative liability, gross amounts offset	(3)	0
Derivative Liability	8	47
Southern Power [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	4	4
Derivative liability, gross	1	1
Southern Power [Member] | Energy-related derivatives | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	22	7
Derivative asset, gross amount offset	(5)	(1)
Derivative Asset	17	6
Derivative liability, gross	63	3
Derivative liability, gross amounts offset	(5)	(1)
Derivative Liability	58	2
Southern Power [Member] | Energy-related derivatives | Other deferred charges and assets [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	3	1
Southern Power [Member] | Energy-related derivatives | Other deferred credits and liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	1	1
Southern Power [Member] | Interest rate derivatives | Other current assets [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	1	3
Southern Power [Member] | Interest rate derivatives | Other Current Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	0	0
Hedging Instruments for Regulatory Purposes [Member] | Parent Company [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	98	3
Derivative liability, gross	60	217
Hedging Instruments for Regulatory Purposes [Member] | Parent Company [Member] | Energy-related derivatives | Other current assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	73	3
Hedging Instruments for Regulatory Purposes [Member] | Parent Company [Member] | Energy-related derivatives | Liabilities from risk management activities, net of collateral [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	27	130
Hedging Instruments for Regulatory Purposes [Member] | Parent Company [Member] | Energy-related derivatives | Other deferred charges and assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	25	0
Hedging Instruments for Regulatory Purposes [Member] | Parent Company [Member] | Energy-related derivatives | Other deferred credits and liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	33	87
Hedging Instruments for Regulatory Purposes [Member] | Parent Company [Member] | Interest rate derivatives | Liabilities from risk management activities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	0	0
Hedging Instruments for Regulatory Purposes [Member] | Alabama Power [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	20	1
Derivative liability, gross	9	55
Hedging Instruments for Regulatory Purposes [Member] | Alabama Power [Member] | Energy-related derivatives | Other current assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	13	1
Hedging Instruments for Regulatory Purposes [Member] | Alabama Power [Member] | Energy-related derivatives | Other deferred charges and assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	7	0
Hedging Instruments for Regulatory Purposes [Member] | Alabama Power [Member] | Energy-related derivatives | Other Current Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	5	40
Hedging Instruments for Regulatory Purposes [Member] | Alabama Power [Member] | Energy-related derivatives | Other deferred credits and liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	4	15
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	44	2
Derivative liability, gross	8	15
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Energy-related derivatives | Other current assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	30	2
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Energy-related derivatives | Other deferred charges and assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	14	0
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Energy-related derivatives | Other Current Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	1	12
Hedging Instruments for Regulatory Purposes [Member] | Georgia Power [Member] | Energy-related derivatives | Other deferred credits and liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	7	3
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Energy-related derivatives
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	5	0
Derivative liability, gross	29	100
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Energy-related derivatives | Other current assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	4	0
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Energy-related derivatives | Liabilities from risk management activities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	12	49
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Energy-related derivatives | Other deferred charges and assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	1	0
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Energy-related derivatives | Other deferred credits and liabilities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	17	51
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Interest rate derivatives | Other current assets [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	0	1
Hedging Instruments for Regulatory Purposes [Member] | Gulf Power [Member] | Interest rate derivatives | Liabilities from risk management activities [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	0	0
Hedging Instruments for Regulatory Purposes [Member] | Mississippi Power [Member] | Energy-related derivatives | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	4	0
Derivative liability, gross	11	47
Hedging Instruments for Regulatory Purposes [Member] | Mississippi Power [Member] | Energy-related derivatives | Other current assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	2	0
Hedging Instruments for Regulatory Purposes [Member] | Mississippi Power [Member] | Energy-related derivatives | Other deferred charges and assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	2	0
Hedging Instruments for Regulatory Purposes [Member] | Mississippi Power [Member] | Energy-related derivatives | Other Current Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	6	29
Hedging Instruments for Regulatory Purposes [Member] | Mississippi Power [Member] | Energy-related derivatives | Other deferred credits and liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	5	18
Cash Flow and Fair Value Hedging [Member] | Parent Company [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	36	22
Derivative liability, gross	94	32
Cash Flow and Fair Value Hedging [Member] | Parent Company [Member] | Energy-related derivatives | Other current assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	23	3
Cash Flow and Fair Value Hedging [Member] | Parent Company [Member] | Energy-related derivatives | Liabilities from risk management activities, net of collateral [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	7	2
Cash Flow and Fair Value Hedging [Member] | Parent Company [Member] | Foreign currency derivatives | Other current assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	0	0
Cash Flow and Fair Value Hedging [Member] | Parent Company [Member] | Foreign currency derivatives | Other deferred charges and assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	0	0
Cash Flow and Fair Value Hedging [Member] | Parent Company [Member] | Foreign currency derivatives | Other Current Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	25	0
Cash Flow and Fair Value Hedging [Member] | Parent Company [Member] | Foreign currency derivatives | Other deferred credits and liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	33	0
Cash Flow and Fair Value Hedging [Member] | Parent Company [Member] | Interest rate derivatives | Other current assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	12	19
Cash Flow and Fair Value Hedging [Member] | Parent Company [Member] | Interest rate derivatives | Liabilities from risk management activities, net of collateral [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	1	23
Cash Flow and Fair Value Hedging [Member] | Parent Company [Member] | Interest rate derivatives | Other deferred charges and assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	1	0
Cash Flow and Fair Value Hedging [Member] | Parent Company [Member] | Interest rate derivatives | Other deferred credits and liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	28	7
Cash Flow and Fair Value Hedging [Member] | Alabama Power [Member] | Interest rate derivatives | Other current assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	0	0
Cash Flow and Fair Value Hedging [Member] | Alabama Power [Member] | Interest rate derivatives | Other Current Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	0	15
Cash Flow and Fair Value Hedging [Member] | Georgia Power [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	2	5
Derivative liability, gross	3	6
Cash Flow and Fair Value Hedging [Member] | Georgia Power [Member] | Interest rate derivatives | Other current assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	2	5
Cash Flow and Fair Value Hedging [Member] | Georgia Power [Member] | Interest rate derivatives | Other deferred charges and assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	0	0
Cash Flow and Fair Value Hedging [Member] | Georgia Power [Member] | Interest rate derivatives | Other Current Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	0	0
Cash Flow and Fair Value Hedging [Member] | Georgia Power [Member] | Interest rate derivatives | Other deferred credits and liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	3	6
Cash Flow and Fair Value Hedging [Member] | Mississippi Power [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	3	0
Derivative liability, gross	0	0
Cash Flow and Fair Value Hedging [Member] | Mississippi Power [Member] | Interest rate derivatives | Other current assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	2	0
Cash Flow and Fair Value Hedging [Member] | Mississippi Power [Member] | Interest rate derivatives | Other deferred charges and assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	1	0
Cash Flow and Fair Value Hedging [Member] | Mississippi Power [Member] | Interest rate derivatives | Other Current Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	0	0
Cash Flow and Fair Value Hedging [Member] | Mississippi Power [Member] | Interest rate derivatives | Other deferred credits and liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	0	0
Cash Flow and Fair Value Hedging [Member] | Southern Power [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	18	3
Derivative liability, gross	62	2
Cash Flow and Fair Value Hedging [Member] | Southern Power [Member] | Energy-related derivatives | Other current assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	18	3
Cash Flow and Fair Value Hedging [Member] | Southern Power [Member] | Energy-related derivatives | Other Current Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	4	2
Cash Flow and Fair Value Hedging [Member] | Southern Power [Member] | Foreign currency derivatives | Other current assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	0	0
Cash Flow and Fair Value Hedging [Member] | Southern Power [Member] | Foreign currency derivatives | Other deferred charges and assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	0	0
Cash Flow and Fair Value Hedging [Member] | Southern Power [Member] | Foreign currency derivatives | Other Current Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	25	0
Cash Flow and Fair Value Hedging [Member] | Southern Power [Member] | Foreign currency derivatives | Other deferred credits and liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	33	0
Successor [Member] | Southern Company Gas [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	581
Derivative asset, gross amount offset	(435)
Derivative Asset	146
Derivative liability, gross	569
Derivative liability, gross amounts offset	(497)
Derivative Liability	72
Collateral already posted, aggregate fair value	62	96
Successor [Member] | Southern Company Gas [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	552
Derivative liability, gross	563
Successor [Member] | Southern Company Gas [Member] | Energy-related derivatives
Fair value of energy-related derivatives and interest rate derivatives
Collateral already posted, aggregate fair value	8
Successor [Member] | Southern Company Gas [Member] | Energy-related derivatives | Liabilities from risk management activities [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	482
Successor [Member] | Southern Company Gas [Member] | Energy-related derivatives | Other deferred charges and assets [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	66
Successor [Member] | Southern Company Gas [Member] | Energy-related derivatives | Assets From Risk Management Activities [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	486
Successor [Member] | Southern Company Gas [Member] | Energy-related derivatives | Other deferred credits and liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	81
Successor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Southern Company Gas [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	25
Derivative liability, gross	3
Successor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Southern Company Gas [Member] | Energy-related derivatives | Liabilities from risk management activities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	3
Successor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Southern Company Gas [Member] | Energy-related derivatives | Other deferred charges and assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	1
Successor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Southern Company Gas [Member] | Energy-related derivatives | Assets From Risk Management Activities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	24
Successor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Southern Company Gas [Member] | Energy-related derivatives | Other deferred credits and liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	0
Successor [Member] | Cash Flow and Fair Value Hedging [Member] | Southern Company Gas [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	4
Derivative liability, gross	3
Successor [Member] | Cash Flow and Fair Value Hedging [Member] | Southern Company Gas [Member] | Energy-related derivatives | Liabilities from risk management activities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	3
Successor [Member] | Cash Flow and Fair Value Hedging [Member] | Southern Company Gas [Member] | Energy-related derivatives | Other deferred charges and assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	0
Successor [Member] | Cash Flow and Fair Value Hedging [Member] | Southern Company Gas [Member] | Energy-related derivatives | Assets From Risk Management Activities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	4
Successor [Member] | Cash Flow and Fair Value Hedging [Member] | Southern Company Gas [Member] | Energy-related derivatives | Other deferred credits and liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	0
Successor [Member] | Cash Flow and Fair Value Hedging [Member] | Southern Company Gas [Member] | Interest rate derivatives | Liabilities from risk management activities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross	0
Successor [Member] | Cash Flow and Fair Value Hedging [Member] | Southern Company Gas [Member] | Interest rate derivatives | Assets From Risk Management Activities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross	$ 0
Predecessor [Member] | Southern Company Gas [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross		942
Derivative asset, gross amount offset		(724)
Derivative Asset		218
Derivative liability, gross		866
Derivative liability, gross amounts offset		(820)
Derivative Liability		46
Predecessor [Member] | Southern Company Gas [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross		920
Derivative liability, gross		829
Predecessor [Member] | Southern Company Gas [Member] | Energy-related derivatives
Fair value of energy-related derivatives and interest rate derivatives
Collateral already posted, aggregate fair value		19
Predecessor [Member] | Southern Company Gas [Member] | Energy-related derivatives | Liabilities from risk management activities [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross		644
Predecessor [Member] | Southern Company Gas [Member] | Energy-related derivatives | Other deferred charges and assets [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross		179
Predecessor [Member] | Southern Company Gas [Member] | Energy-related derivatives | Assets From Risk Management Activities [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross		741
Predecessor [Member] | Southern Company Gas [Member] | Energy-related derivatives | Other deferred credits and liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross		185
Predecessor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Southern Company Gas [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross		10
Derivative liability, gross		30
Predecessor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Southern Company Gas [Member] | Energy-related derivatives | Liabilities from risk management activities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross		28
Predecessor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Southern Company Gas [Member] | Energy-related derivatives | Other deferred charges and assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross		0
Predecessor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Southern Company Gas [Member] | Energy-related derivatives | Assets From Risk Management Activities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross		10
Predecessor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Southern Company Gas [Member] | Energy-related derivatives | Other deferred credits and liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross		2
Predecessor [Member] | Cash Flow and Fair Value Hedging [Member] | Southern Company Gas [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross		12
Derivative liability, gross		7
Predecessor [Member] | Cash Flow and Fair Value Hedging [Member] | Southern Company Gas [Member] | Energy-related derivatives | Liabilities from risk management activities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross		5
Predecessor [Member] | Cash Flow and Fair Value Hedging [Member] | Southern Company Gas [Member] | Energy-related derivatives | Other deferred charges and assets [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross		0
Predecessor [Member] | Cash Flow and Fair Value Hedging [Member] | Southern Company Gas [Member] | Energy-related derivatives | Assets From Risk Management Activities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross		3
Predecessor [Member] | Cash Flow and Fair Value Hedging [Member] | Southern Company Gas [Member] | Energy-related derivatives | Other deferred credits and liabilities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross		2
Predecessor [Member] | Cash Flow and Fair Value Hedging [Member] | Southern Company Gas [Member] | Interest rate derivatives | Liabilities from risk management activities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative liability, gross		0
Predecessor [Member] | Cash Flow and Fair Value Hedging [Member] | Southern Company Gas [Member] | Interest rate derivatives | Assets From Risk Management Activities [Member] | Designated as Hedging Instrument [Member]
Fair value of energy-related derivatives and interest rate derivatives
Derivative asset, gross		$ 9