Summary of Significant Accounting Policies - Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions		12 Months Ended
	Jan. 01, 2014	Dec. 31, 2015	Dec. 31, 2014
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 5,564	$ 4,664
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Amortization of Regulatory Asset, Vacation Pay		1 year
Other cost of removal obligations [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ (1,177)	(1,229)
Over recovered regulatory clause revenues [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(261)	(48)
Deferred income tax credits [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(187)	(192)
Property damage reserves-liability [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(178)	(181)
Asset retirement obligations-liability [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(45)	(130)
Other regulatory liabilities [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(35)	(47)
Kemper regulatory liability (Mirror CWIP) [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		0	(271)
Retiree benefit plans [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		3,440	3,469
Deferred income tax charges [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		1,514	1,458
Asset retirement obligations-liability [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		481	119
Other regulatory assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		299	275
Loss on reacquired debt [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		248	267
Fuel hedging-asset [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		225	202
Kemper IGCC regulatory assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		216	148
Vacation pay [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		178	177
Deferred PPA charges [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		163	185
Under recovered regulatory clause revenues [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		142	157
Remaining net book value of retired units [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		283	44
Environmental remediation-asset [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		78	64
Property damage reserves - asset [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		92	98
Nuclear outage [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 88	99
Maximum [Member]
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Recovery and Amortization Periods for Regulatory Assets Liabilities Average Remaining Service Period		15 years
Life of New Issue		50 years
Fuel Hedging Assets and Liabilities, Amortization Period		5 years
Power Purchase Agreement Period		8 years
Recovered and Amortized as Approved by Appropriate State PSCs		11 years
Amortization Period For Other Regulatory Liabilities		15 years
Maximum [Member] | Other regulatory assets [Member]
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Amortization Period For Other Regulatory Assets		15 years
Maximum [Member] | Property damage reserves - asset [Member]
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Amortization Period For Other Regulatory Assets		6 years
Maximum [Member] | Asset Group 1 [Member]
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Amortization Period For Other Regulatory Assets		10 years
Gulf Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 296	319
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Life of New Issue		40 years
Fuel Hedging Assets and Liabilities, Amortization Period		5 years
Amortization of Regulatory Asset, Vacation Pay		1 year
Recovered and Amortized as Approved by Appropriate State PSCs		1 year
Gulf Power [Member] | Other cost of removal obligations [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ (262)	(243)
Gulf Power [Member] | Over recovered regulatory clause revenues [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(22)	0
Gulf Power [Member] | Deferred income tax credits [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(3)	(4)
Gulf Power [Member] | Property damage reserves-liability [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(38)	(35)
Gulf Power [Member] | Asset retirement obligations-liability [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(1)	(5)
Gulf Power [Member] | Retiree benefit plans [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		147	148
Gulf Power [Member] | Deferred income tax charges [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		59	53
Gulf Power [Member] | Other regulatory assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		7	9
Gulf Power [Member] | Loss on reacquired debt [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		15	16
Gulf Power [Member] | Fuel hedging-asset [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		104	73
Gulf Power [Member] | Vacation pay [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		10	10
Gulf Power [Member] | Deferred return on transmission upgrades [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		10	0
Gulf Power [Member] | Deferred PPA charges [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		163	185
Gulf Power [Member] | Under recovered regulatory clause revenues [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		1	53
Gulf Power [Member] | Environmental remediation-asset [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		46	48
Gulf Power [Member] | Deferred income tax charges - Medicare subsidy [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		2	3
Gulf Power [Member] | Regulatory Cost of Removal Credit [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		29	8
Gulf Power [Member] | Ash Pond Closure [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 29	0
Gulf Power [Member] | Maximum [Member]
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Recovery and Amortization Periods for Regulatory Assets Liabilities Average Remaining Service Period		14 years
Life of Related Property Over which Deferred Income Tax Liabilities are Amortized		65 years
Recovered and Amortized as Approved by Appropriate State PSCs		14 years
Recovered and Amortization Periods as Approved by Appropriate State Public Service Commission		8 years
Gulf Power [Member] | Maximum [Member] | Generation Site Selection Evaluation Costs [Member]
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Recovered and Amortized as Approved by Appropriate State PSCs		8 years
Alabama Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 791	738
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Fuel Hedging Assets and Liabilities, Amortization Period		3 years 6 months
Amortization of Regulatory Asset, Vacation Pay		1 year
Medicare Drug Subsidy Obligation Related To Subsidiary		$ 17	18
Amortization Period for Regulatory Deferrals		11 years
Alabama Power [Member] | Other cost of removal obligations [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ (722)	(744)
Alabama Power [Member] | Deferred income tax credits [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(70)	(72)
Alabama Power [Member] | Asset retirement obligations-liability [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(40)	(125)
Alabama Power [Member] | Other regulatory liabilities [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(8)	(17)
Alabama Power [Member] | Nuclear disaster reserve [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(75)	(84)
Alabama Power [Member] | Retiree benefit plans [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		903	882
Alabama Power [Member] | Deferred income tax charges [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		522	525
Alabama Power [Member] | Other regulatory assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		53	49
Alabama Power [Member] | Loss on reacquired debt [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		75	80
Alabama Power [Member] | Fuel hedging-asset [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		55	53
Alabama Power [Member] | Vacation pay [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		66	65
Alabama Power [Member] | Under recovered regulatory clause revenues [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(97)	57
Alabama Power [Member] | Nuclear outage [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		53	56
Alabama Power [Member] | Regulatory deferrals [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 76	13
Alabama Power [Member] | Maximum [Member]
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Recovery and Amortization Periods for Regulatory Assets Liabilities Average Remaining Service Period		15 years
Life of Related Property Over which Deferred Income Tax Liabilities are Amortized		50 years
Life of New Issue		50 years
Recovered and Amortized as Approved by Appropriate State PSCs		15 years
Recovery and Amortization Periods for Regulatory Assets Liabilities Approved by PSCs		10 years
Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 2,933	2,529
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Recovery and Amortization Periods for Regulatory Assets Liabilities Average Remaining Service Period		14 years
Other Cost of Removal Obligations Related to Subsidiary		$ 14
Amortization Period of Other Cost of Removal Obligations		12 months
Amortization of Regulatory Asset, Vacation Pay		1 year
Refueling Cycles Maximum Period		24 months
Period for Environmental Construction	9 years	9 years
Georgia Power [Member] | Other cost of removal obligations [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ (31)	(60)
Georgia Power [Member] | Deferred income tax credits [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(105)	(106)
Georgia Power [Member] | Other regulatory liabilities [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(2)	(7)
Georgia Power [Member] | Retiree benefit plans [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		1,307	1,325
Georgia Power [Member] | Deferred income tax charges [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		653	668
Georgia Power [Member] | Asset retirement obligations-liability [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		411	108
Georgia Power [Member] | Other regulatory assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 140	153
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Recovered and Amortized as Approved by Appropriate State PSCs		12 years
Georgia Power [Member] | Loss on reacquired debt [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 150	163
Georgia Power [Member] | Vacation pay [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		91	91
Georgia Power [Member] | Remaining net book value of retired units [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		171	29
Georgia Power [Member] | Canceled construction projects [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 56	67
Georgia Power [Member] | Deferred income tax charges - Medicare subsidy [Member]
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Recovered and Amortized as Approved by Appropriate State PSCs		6 years
Georgia Power [Member] | Storm Reserve [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 92	98
Georgia Power [Member] | Maximum [Member]
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Life of Related Property Over which Deferred Income Tax Liabilities are Amortized		70 years
Life of New Issue		38 years
Recovered and Amortized as Approved by Appropriate State PSCs		10 years
Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 667	172
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Recovery and Amortization Periods for Regulatory Assets Liabilities Average Remaining Service Period		14 years
Fuel Hedging Assets and Liabilities, Amortization Period		3 years
Mississippi Power [Member] | Other cost of removal obligations [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ (167)	(166)
Mississippi Power [Member] | Property damage reserves-liability [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(64)	(62)
Mississippi Power [Member] | Other regulatory liabilities [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		(11)	(13)
Mississippi Power [Member] | Deferred income tax charges [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		291	227
Mississippi Power [Member] | Asset retirement obligations-liability [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		70	11
Mississippi Power [Member] | Other regulatory assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		16	18
Mississippi Power [Member] | Fuel hedging-asset [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		50	47
Mississippi Power [Member] | Vacation pay [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 11	11
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Amortization of Regulatory Asset, Vacation Pay		1 year
Mississippi Power [Member] | Remaining net book value of retired units [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 36	2
Mississippi Power [Member] | Mirror Construction Work In Progress [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		0	(271)
Mississippi Power [Member] | Kemper IGCC [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		216	148
Mississippi Power [Member] | Property tax [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 27	28
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Amortization Period of Regulatory Assets and Liabilities		12 months
Mississippi Power [Member] | Retiree Benefit Plans - Regulatory Assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 163	169
Mississippi Power [Member] | Plant Daniel Units 3 and 4 [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total assets (liabilities), net		$ 29	$ 23
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Recovery and Amortization Periods for Regulatory Assets Liabilities Approved by PSCs		10 years
Regulatory Assets Associated with Asset Retirement Obligations [Member] | Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities - Other Information [Abstract]
Amortization Period of Regulatory Assets and Liabilities		49 years