Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended								6 Months Ended			12 Months Ended			65 Months Ended
	Jun. 30, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	May 31, 2017
Quarterly Financial Information [Line Items]
Tax Cuts And Jobs Act Of 2017, incomplete accounting, provisional income tax expense (benefit)		$ 264
Summarized quarterly financial information
Operating revenues		5,629	$ 6,201	$ 5,430	$ 5,771	$ 5,181	$ 6,264	$ 4,459	$ 3,992				$ 23,031	$ 19,896	$ 17,489
Operating income (loss)		794	2,045	(1,594)	1,306	587	1,917	1,185	940				2,551	4,629	4,282
Income taxes													142	951	1,194
Net income after dividends on preferred and preference stock		$ 496	$ 1,069	$ (1,381)	$ 658	$ 197	$ 1,139	$ 623	$ 489				$ 842	$ 2,448	$ 2,367
Basic (in dollars per share)		$ 0.49	$ 1.07	$ (1.38)	$ 0.66	$ 0.20	$ 1.18	$ 0.67	$ 0.53				$ 0.84	$ 2.57	$ 2.60
Diluted (in dollars per share)		0.49	1.06	(1.37)	0.66	0.20	1.17	0.66	0.53				0.84	2.55	2.59
Cash dividends (in dollars per share)		0.58	0.58	0.58	0.56	0.5600	0.5600	0.5600	0.5425				$ 2.3000	$ 2.2225	$ 2.1525
Trading price range, high, per common share (in dollars per share)		53.51	50.80	51.97	51.47	52.23	54.64	53.64	51.73
Trading price range, low, per common share (in dollars per share)		$ 47.92	$ 46.71	$ 47.87	$ 47.57	$ 46.20	$ 50	$ 47.62	$ 46
GEORGIA POWER CO
Summarized quarterly financial information
Operating revenues		$ 1,884	$ 2,546	$ 2,048	$ 1,832	$ 1,762	$ 2,698	$ 2,051	$ 1,872				$ 8,310	$ 8,383	$ 8,326
Operating income (loss)		470	1,034	639	501	258	1,054	656	509				2,644	2,477	2,348
Income taxes													830	780	769
Net income after dividends on preferred and preference stock		227	580	347	260	113	599	349	269				1,414	1,330	1,260
ALABAMA POWER CO
Summarized quarterly financial information
Operating revenues		1,433	1,740	1,484	1,382	1,329	1,785	1,444	1,331				6,039	5,889	5,768
Operating income (loss)		268	616	454	376	252	650	430	333				1,714	1,665	1,563
Income taxes													568	531	506
Net income after dividends on preferred and preference stock		119	325	230	174	102	351	213	156				848	822	785
GULF POWER CO
Summarized quarterly financial information
Operating revenues		372	437	357	350	349	436	365	335				1,516	1,485	1,483
Operating income (loss)		53	115	75	46	54	90	74	65				289	283	290
Income taxes													90	91	92
Net income after dividends on preferred and preference stock		19	63	35	18	23	45	34	29				135	131	148
After tax charge to income													0
MISSISSIPPI POWER CO
Quarterly Financial Information [Line Items]
Tax Cuts And Jobs Act Of 2017, incomplete accounting, provisional income tax expense (benefit)		372
Summarized quarterly financial information
Operating revenues		271	341	303	272	277	352	277	257				1,187	1,163	1,138
Operating income (loss)		(177)	51	(2,954)	(62)	(166)	9	(28)	(10)				(3,142)	(195)	(173)
Income taxes													(532)	(104)	(72)
Net income after dividends on preferred and preference stock		(556)	40	(2,054)	(20)	(89)	26	2	11				(2,590)	(50)	(8)
SOUTHERN POWER CO
Quarterly Financial Information [Line Items]
Tax Cuts And Jobs Act Of 2017, incomplete accounting, provisional income tax expense (benefit)		(743)
Summarized quarterly financial information
Operating revenues		478	618	529	450	389	500	373	315				2,075	1,577	1,390
Operating income (loss)		32	159	112	65	28	134	81	47				368	290	326
Income taxes		(810)	(39)	(38)	(52)	(29)	(102)	(41)	(23)				(939)	(195)	21
Net income after dividends on preferred and preference stock		795	124	82	70	23	176	89	50
SOUTHERN Co GAS
Summarized quarterly financial information
Operating revenues		1,079	565	716	1,560	1,109	543				$ 1,652		3,920
Operating income (loss)		110	68	96	391	185	12				197		665
Income taxes											76		367
EBIT		129	118	128	435	221	50
Net income after dividends on preferred and preference stock		(60)	15	49	239	110	4				$ 114		243
Kemper IGCC
Summarized quarterly financial information
Pre-Tax charge to income		208	34	3,000	108	206	88	81	53
After tax charge to income		185	21	2,100	67	127	54	50	33				$ 2,400	$ 264	226
Kemper IGCC | MISSISSIPPI POWER CO
Summarized quarterly financial information
Pre-Tax charge to income	$ 2,800	208	34	3,000	108	206	88	81	53	$ 242						$ 3,070
After tax charge to income	$ 2,000	$ 185	$ 21	$ 2,100	$ 67	$ 127	$ 54	50	33	$ 206						$ 1,890
Predecessor | SOUTHERN Co GAS
Summarized quarterly financial information
Operating revenues								571	1,334			$ 1,905			3,941
Operating income (loss)								(27)	348			321			746
Income taxes												87			213
EBIT								(23)	351			328			761
Net income after dividends on preferred and preference stock								$ (51)	$ 182			$ 131			$ 353