QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Details) - USD ($)		1 Months Ended		3 Months Ended								6 Months Ended	12 Months Ended			65 Months Ended
	Jan. 01, 2019	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 31, 2017
Summarized quarterly financial information
Operating revenues				$ 4,914,000,000	$ 5,995,000,000	$ 5,098,000,000	$ 5,412,000,000	$ 5,337,000,000	$ 6,159,000,000	$ 5,627,000,000	$ 6,372,000,000
Operating Income				690,000,000	2,013,000,000	1,342,000,000	3,691,000,000	578,000,000	2,174,000,000	63,000,000	1,376,000,000		$ 7,736,000,000	$ 4,191,000,000	$ 2,333,000,000
Net Income (Loss)				409,000,000	1,345,000,000	931,000,000	2,059,000,000	269,000,000	1,222,000,000	(127,000,000)	936,000,000		4,739,000,000	2,226,000,000	842,000,000
Consolidated Net Income Attributable to Southern Company				440,000,000	$ 1,316,000,000	$ 899,000,000	$ 2,084,000,000	$ 278,000,000	$ 1,164,000,000	$ (154,000,000)	$ 938,000,000
Gain (loss) on dispositions													(2,569,000,000)	(291,000,000)	(40,000,000)
Impairment charges													168,000,000	210,000,000	0
Lease, impairment loss				17,000,000
Lease, impairment loss, after tax				13,000,000
Income taxes													$ 1,798,000,000	$ 449,000,000	$ 142,000,000
Impairment charges				$ 0
Basic (in dollars per share)				$ 0.42	$ 1.26	$ 0.86	$ 2.01	$ 0.27	$ 1.14	$ (0.15)	$ 0.93		$ 4.53	$ 2.18	$ 0.84
Diluted (in dollars per share)				$ 0.42	$ 1.25	$ 0.85	$ 1.99	$ 0.27	$ 1.13	$ (0.15)	$ 0.92		$ 4.50	$ 2.17	$ 0.84
Alabama Power
Summarized quarterly financial information
Operating revenues				$ 1,363,000,000	$ 1,841,000,000	$ 1,513,000,000	$ 1,408,000,000	$ 1,316,000,000	$ 1,740,000,000	$ 1,503,000,000	$ 1,473,000,000
Operating Income				134,000,000	676,000,000	445,000,000	338,000,000	164,000,000	561,000,000	380,000,000	372,000,000		$ 1,593,000,000	$ 1,477,000,000	$ 1,657,000,000
Net Income (Loss)				88,000,000	469,000,000	296,000,000	217,000,000	73,000,000	373,000,000	259,000,000	225,000,000		1,070,000,000	930,000,000	848,000,000
Consolidated Net Income Attributable to Southern Company				88,000,000	469,000,000	296,000,000	217,000,000	73,000,000	373,000,000	259,000,000	225,000,000
Income taxes													270,000,000	291,000,000	568,000,000
Georgia Power
Summarized quarterly financial information
Operating revenues				1,703,000,000	2,755,000,000	2,117,000,000	1,833,000,000	1,818,000,000	2,593,000,000	2,048,000,000	1,961,000,000
Operating Income				205,000,000	1,161,000,000	647,000,000	448,000,000	257,000,000	991,000,000	(472,000,000)	513,000,000		2,461,000,000	1,289,000,000	2,573,000,000
Net Income (Loss)				122,000,000	839,000,000	448,000,000	311,000,000	173,000,000	664,000,000	(396,000,000)	352,000,000		1,720,000,000	793,000,000	1,414,000,000
Consolidated Net Income Attributable to Southern Company				122,000,000	839,000,000	448,000,000	311,000,000	173,000,000	664,000,000	(396,000,000)	352,000,000
Income taxes													472,000,000	214,000,000	830,000,000
Mississippi Power
Summarized quarterly financial information
Operating revenues				294,000,000	370,000,000	313,000,000	287,000,000	308,000,000	358,000,000	297,000,000	302,000,000
Operating Income				22,000,000	93,000,000	54,000,000	56,000,000	52,000,000	80,000,000	54,000,000	7,000,000		225,000,000	193,000,000	(3,151,000,000)
Net Income (Loss)				0	65,000,000	37,000,000	37,000,000	149,000,000	47,000,000	46,000,000	(7,000,000)		139,000,000	235,000,000	(2,590,000,000)
Consolidated Net Income Attributable to Southern Company				0	65,000,000	37,000,000	37,000,000	149,000,000	47,000,000	46,000,000	(7,000,000)
Pre-tax charge (credit) to income								(9,000,000)
After tax charge (credit) to income								(95,000,000)
Income taxes													30,000,000	(102,000,000)	(532,000,000)
Southern Power
Summarized quarterly financial information
Operating revenues				411,000,000	574,000,000	510,000,000	443,000,000	506,000,000	635,000,000	555,000,000	509,000,000
Operating Income				15,000,000	167,000,000	153,000,000	60,000,000	30,000,000	136,000,000	16,000,000	60,000,000		395,000,000	242,000,000	368,000,000
Net Income (Loss)				(12,000,000)	111,000,000	203,000,000	27,000,000	(60,000,000)	146,000,000	45,000,000	115,000,000		339,000,000	187,000,000	1,071,000,000
Consolidated Net Income Attributable to Southern Company				23,000,000	86,000,000	174,000,000	56,000,000	(48,000,000)	92,000,000	22,000,000	121,000,000				1,071,000,000
Impairment charges													3,000,000	156,000,000	0
After tax impairment charges														117,000,000
Income taxes								75,000,000					(56,000,000)	(164,000,000)	(939,000,000)
Southern Company Gas
Summarized quarterly financial information
Operating revenues				1,131,000,000	498,000,000	689,000,000	1,474,000,000	1,048,000,000	492,000,000	730,000,000	1,639,000,000
Operating Income				318,000,000	(35,000,000)	134,000,000	353,000,000	104,000,000	374,000,000	49,000,000	388,000,000		770,000,000	915,000,000	660,000,000
Net Income (Loss)				238,000,000	(29,000,000)	106,000,000	270,000,000	78,000,000	46,000,000	(31,000,000)	279,000,000		585,000,000	372,000,000	243,000,000
Consolidated Net Income Attributable to Southern Company				238,000,000	(29,000,000)	106,000,000	270,000,000	78,000,000	46,000,000	(31,000,000)	279,000,000
Gain (loss) on dispositions													0	(291,000,000)	0
Income taxes													130,000,000	464,000,000	367,000,000
Impairment charges				0									115,000,000	42,000,000	$ 0
Plant Vogtle Units 3 And 4 | Georgia Power
Summarized quarterly financial information
Estimated loss on plants under construction										1,100,000,000
Kemper IGCC | Mississippi Power
Summarized quarterly financial information
Pre-tax charge (credit) to income			$ 2,800,000,000								44,000,000	$ 242,000,000	24,000,000	$ 37,000,000		$ 3,070,000,000.00
After tax charge (credit) to income			$ 2,000,000,000.0								33,000,000	$ 206,000,000				$ 1,890,000,000
Florida Plants | Southern Power
Summarized quarterly financial information
Impairment charges										119,000,000
After tax impairment charges										89,000,000
Natural Gas Storage Facility | Southern Company Gas
Summarized quarterly financial information
Impairment charges													115,000,000
After tax impairment charges													86,000,000
Wind Turbine Equipment | Southern Power
Summarized quarterly financial information
Impairment charges									36,000,000
After tax impairment charges									27,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Summarized quarterly financial information
Gain (loss) on dispositions								(27,000,000)	353,000,000	(36,000,000)
Gain (loss) on dispositions, after tax								$ (15,000,000)	$ 40,000,000	$ (76,000,000)
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Gulf Power
Summarized quarterly financial information
Gain (loss) on dispositions	$ 2,600,000,000			70,000,000	4,000,000	(15,000,000)	2,500,000,000						2,600,000,000
Gain (loss) on dispositions, after tax	$ 1,400,000,000			102,000,000	4,000,000	(11,000,000)	1,300,000,000						1,400,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | PowerSecure International, Inc. Lighting Business
Summarized quarterly financial information
Gain (loss) on dispositions													(58,000,000)
Gain (loss) on dispositions, after tax													(52,000,000)
Impairment charges				12,000,000	14,000,000	32,000,000
After tax impairment charges				5,000,000	15,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Plant Nacogdoches | Southern Power
Summarized quarterly financial information
Gain (loss) on dispositions						23,000,000							23,000,000
Gain (loss) on dispositions, after tax						88,000,000							88,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Pivotal Home Solutions | Southern Company Gas
Summarized quarterly financial information
Gain (loss) on dispositions													(24,000,000)
Gain (loss) on dispositions, after tax		$ (67,000,000)											(17,000,000)
Impairment charges											$ 42,000,000		$ 42,000,000
Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations | Gasifier-Related Assets | Mississippi Power
Summarized quarterly financial information
Pre-tax charge (credit) to income				14,000,000	4,000,000	4,000,000	2,000,000
After tax charge (credit) to income				17,000,000	3,000,000	$ 3,000,000	$ 1,000,000
LOUISIANA | Natural Gas Storage Facility | Southern Company Gas
Summarized quarterly financial information
Impairment charges				(1,000,000)	92,000,000
After tax impairment charges				$ 4,000,000	$ 65,000,000