Segment and Related Information - Financial Data for Business Segments and Products and Services (Details) - USD ($) $ in Millions	3 Months Ended								6 Months Ended		9 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Jun. 30, 2016	Oct. 03, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financial data for business segments
Operating revenues	$ 5,181	$ 6,264	$ 4,459	$ 3,992	$ 3,568	$ 5,401	$ 4,337	$ 4,183				$ 19,896	$ 17,489	$ 18,467
Depreciation and amortization												2,502	2,034	1,945
Depreciation and amortization												2,923	2,395	2,293
Earnings from equity method investments											$ 15	59	0	0
Interest income												20	23	19
Interest expense												(1,317)	(840)	(835)
Income taxes												951	1,194	977
Segment net income (loss)	197	1,139	623	489	271	959	629	508				2,448	2,367	1,963
Gross property additions												7,624	6,169	6,522
Total assets	109,697				78,318				$ 109,697			109,697	78,318	70,233
Segment and Related Information (Textual) [Abstract]
Estimated loss on Kemper IGCC												428	365	868
Unamortized Debt Issuance Expense	213				241				213			213	241	202
Kemper IGCC [Member]
Segment and Related Information (Textual) [Abstract]
After Tax Charge To Income	127	54	50	33	113	93	14	6				264	226	536
Electric Utilities [Member]
Financial data for business segments
Operating revenues												17,941	17,442	18,406
Depreciation and amortization												2,233	2,020	1,929
Earnings from equity method investments												2	1	1
Interest income												13	22	18
Interest expense												(931)	(774)	(794)
Income taxes												1,091	1,326	1,053
Segment net income (loss)												2,571	2,401	1,969
Gross property additions												6,966	6,129	6,510
Total assets	86,994				77,560				86,994			86,994	77,560	69,402
Traditional Operating Companies | Electric Utilities [Member]
Financial data for business segments
Operating revenues												16,803	16,491	17,354
Depreciation and amortization												1,881	1,772	1,709
Earnings from equity method investments												2	1	1
Interest income												6	19	17
Interest expense												(814)	(697)	(705)
Income taxes												1,286	1,305	1,056
Segment net income (loss)												2,233	2,186	1,797
Gross property additions												4,852	5,124	5,568
Total assets	72,141				69,052				72,141			72,141	69,052	64,300
Southern Power [Member]
Financial data for business segments
Operating revenues												419	417	383
Southern Power [Member] | Electric Utilities [Member]
Financial data for business segments
Operating revenues												1,577	1,390	1,501
Depreciation and amortization												352	248	220
Earnings from equity method investments												0	0	0
Interest income												7	2	1
Interest expense												(117)	(77)	(89)
Income taxes												(195)	21	(3)
Segment net income (loss)												338	215	172
Gross property additions												2,114	1,005	942
Total assets	15,169				8,905				15,169			15,169	8,905	5,233
Southern Company Gas [Member] | Electric Utilities [Member]
Financial data for business segments
Operating revenues												1,652	0	0
Depreciation and amortization												238	0	0
Earnings from equity method investments												60	0	0
Interest income												2	0	0
Interest expense												(81)	0	0
Income taxes												76	0	0
Segment net income (loss)												114	0	0
Gross property additions												618	0	0
Total assets	21,853				0				21,853			21,853	0	0
All Other [Member]
Financial data for business segments
Operating revenues												463	152	159
Depreciation and amortization												31	14	16
Earnings from equity method investments												(3)	(1)	(1)
Interest income												20	6	3
Interest expense												(317)	(69)	(43)
Income taxes												(216)	(132)	(76)
Segment net income (loss)												(230)	(32)	(3)
Gross property additions												41	40	11
Total assets	2,474				1,819				2,474			2,474	1,819	1,143
Intersegment Eliminations [Member]
Financial data for business segments
Operating revenues												(160)	(105)	(98)
Depreciation and amortization												0	0	0
Earnings from equity method investments												0	0	0
Interest income												(15)	(5)	(2)
Interest expense												12	3	2
Income taxes												0	0	0
Segment net income (loss)												(7)	(2)	(3)
Gross property additions												(1)	0	1
Total assets	(1,624)				(1,061)				(1,624)			(1,624)	(1,061)	(312)
Intersegment Eliminations [Member] | Electric Utilities [Member]
Financial data for business segments
Operating revenues												(439)	(439)	(449)
Depreciation and amortization												0	0	0
Earnings from equity method investments												0	0	0
Interest income												0	1	0
Interest expense												0	0	0
Income taxes												0	0	0
Segment net income (loss)												0	0	0
Gross property additions												0	0	0
Total assets	(316)				(397)				(316)			(316)	(397)	(131)
Deferred Tax Liability, Noncurrent [Member]
Segment and Related Information (Textual) [Abstract]
Prior period reclassification adjustment														488
Successor [Member] | Southern Company Gas [Member]
Financial data for business segments
Operating revenues	1,109	543							1,652
Depreciation and amortization									238
Earnings from equity method investments									60
EBIT	221	50
Interest expense									(81)
Income taxes									76
Segment net income (loss)	110	$ 4							114
Gross property additions									632
Total assets	21,853								21,853			21,853
Successor [Member] | Southern Company Gas [Member] | Operating Segments [Member]
Financial data for business segments
Operating revenues									1,751
Depreciation and amortization									230
Earnings from equity method investments									58
Interest expense									(125)
Income taxes									71
Segment net income (loss)									116
Gross property additions									621
Total assets	24,875								24,875			24,875
Successor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | Gas Distribution Operations [Member]
Financial data for business segments
Operating revenues									1,342
Depreciation and amortization									185
Earnings from equity method investments									0
Interest expense									(105)
Income taxes									51
Segment net income (loss)									77
Gross property additions									561
Total assets	19,453								19,453			19,453
Successor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | Gas Marketing Services [Member]
Financial data for business segments
Operating revenues									354
Depreciation and amortization									35
Earnings from equity method investments									0
Interest expense									(1)
Income taxes									7
Segment net income (loss)									19
Gross property additions									5
Total assets	2,084								2,084			2,084
Successor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Financial data for business segments
Operating revenues									24
Cost of Revenue									6,116
Depreciation and amortization									1
Earnings from equity method investments									0
Interest expense									(3)
Income taxes									(3)
Segment net income (loss)									0
Gross property additions									1
Total assets	1,127								1,127			1,127
Successor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | Gas Midstream Operations [Member]
Financial data for business segments
Operating revenues									31
Depreciation and amortization									9
Earnings from equity method investments									58
Interest expense									(16)
Income taxes									16
Segment net income (loss)									20
Gross property additions									54
Total assets	2,211								2,211			2,211
Successor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | All Other [Member]
Financial data for business segments
Operating revenues									3
Depreciation and amortization									8
Earnings from equity method investments									2
Interest expense									44
Income taxes									5
Segment net income (loss)									(2)
Gross property additions									11
Total assets	11,145								11,145			11,145
Successor [Member] | Southern Company Gas [Member] | Intersegment Eliminations [Member]
Financial data for business segments
Operating revenues									(102)
Depreciation and amortization									0
Earnings from equity method investments									0
Interest expense									0
Income taxes									0
Segment net income (loss)									0
Gross property additions									0
Total assets	$ (14,167)								(14,167)			$ (14,167)
Predecessor [Member] | Southern Company Gas [Member]
Financial data for business segments
Operating revenues			571	1,334	962	584	674	1,721		$ 1,905			3,941	5,385
Depreciation and amortization										206			397	380
Earnings from equity method investments										2			6	8
EBIT			(23)	351	221	62	111	367		328			761	1,112
Interest expense										(96)			(175)	(182)
Income taxes										87			213	350
Segment net income (loss)			$ (51)	$ 182	107	$ 11	$ 42	$ 193		131			353	482
Gross property additions										548			1,027	769
Total assets					14,754								14,754	14,862
Predecessor [Member] | Southern Company Gas [Member] | Operating Segments [Member]
Financial data for business segments
Operating revenues										2,003			4,141	5,661
Depreciation and amortization										199			380	364
EBIT										388			820	1,122
Gross property additions										532			993	743
Total assets					14,832								14,832	14,804
Predecessor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | Gas Distribution Operations [Member]
Financial data for business segments
Operating revenues										1,575			3,049	4,001
Depreciation and amortization										178			336	317
EBIT										353			581	582
Gross property additions										484			957	715
Total assets					12,519								12,519	12,038
Predecessor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | Gas Marketing Services [Member]
Financial data for business segments
Operating revenues										435			835	994
Depreciation and amortization										11			25	28
EBIT										109			152	132
Gross property additions										4			7	11
Total assets					686								686	670
Predecessor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Financial data for business segments
Operating revenues										(32)			202	578
Cost of Revenue										2,675			6,492	10,849
Depreciation and amortization										1			1	1
EBIT										(68)			110	425
Gross property additions										1			2	2
Total assets					935								935	1,402
Predecessor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | Gas Midstream Operations [Member]
Financial data for business segments
Operating revenues										25			55	88
Depreciation and amortization										9			18	18
EBIT										(6)			(23)	(17)
Gross property additions										43			27	15
Total assets					692								692	694
Predecessor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | All Other [Member]
Financial data for business segments
Operating revenues										4			11	7
Depreciation and amortization										7			17	16
EBIT										(60)			(59)	(10)
Gross property additions										16			34	26
Total assets					9,662								9,662	9,705
Predecessor [Member] | Southern Company Gas [Member] | Intersegment Eliminations [Member]
Financial data for business segments
Operating revenues										(102)			(211)	(283)
Depreciation and amortization										0			0	0
EBIT										0			0	0
Gross property additions										0			0	0
Total assets					$ (9,740)								(9,740)	(9,647)
Third Party Gross Revenues | Successor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Financial data for business segments
Operating revenues									5,807
Third Party Gross Revenues | Predecessor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Financial data for business segments
Operating revenues										2,500			6,286	10,709
Intercompany Revenues | Successor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Financial data for business segments
Operating revenues									333
Intercompany Revenues | Predecessor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Financial data for business segments
Operating revenues										143			408	718
Total Gross Revenues | Successor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Financial data for business segments
Operating revenues									$ 6,140
Total Gross Revenues | Predecessor [Member] | Southern Company Gas [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Financial data for business segments
Operating revenues										$ 2,643			$ 6,694	$ 11,427