Introduction - ASC 606 (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Condensed Statements of Income
Natural gas revenues	$ 706	$ 684	$ 2,314	$ 2,214
Other revenues	395	184	808	326
Other operations and maintenance	1,559	1,356	3,008	2,740
Operating income (loss)	63	(1,649)	1,439	(397)
Other income (expense), net	78	52	138	98
Earnings (loss) before income taxes	(266)	(1,935)	784	(957)
Income taxes (benefit)	(139)	(587)	(25)	(273)
Net income (loss)	(127)	(1,348)	809	(684)
Consolidated net income attributable to Southern Company	(154)	(1,381)	784	(723)
Condensed Statements of Cash Flows
Net income (loss)	(127)	(1,348)	809	(684)
Changes in certain current assets and liabilities:
Receivables			94	107
Other current assets			(40)	(30)
Accrued taxes			213	(132)
Other current liabilities			125	(14)
Condensed Balance Sheets
Unbilled revenues	769		769		$ 810
Other accounts and notes receivable	621		621		698
Other current assets	172		172		199
Other current liabilities	808		808		874
Retained earnings	8,494		8,494		8,885
Balances Without Adoption of ASC 606
Condensed Statements of Income
Natural gas revenues	713		2,307
Other revenues	393		805
Other operations and maintenance	1,546		2,985
Operating income (loss)	81		1,452
Other income (expense), net	67		118
Earnings (loss) before income taxes	(259)		777
Income taxes (benefit)	(137)		(27)
Net income (loss)	(122)		804
Consolidated net income attributable to Southern Company	(149)		779
Condensed Statements of Cash Flows
Net income (loss)	(122)		804
Changes in certain current assets and liabilities:
Receivables			99
Other current assets			(45)
Accrued taxes			215
Other current liabilities			118
Condensed Balance Sheets
Unbilled revenues	824		824
Other accounts and notes receivable	622		622
Other current assets	116		116
Accrued taxes	542		542
Other current liabilities	815		815
Retained earnings	8,489		8,489
ALABAMA POWER CO
Condensed Statements of Income
Other revenues	69	51	131	108
Other operations and maintenance	402	389	788	772
Operating income (loss)	380	440	752	801
Other income (expense), net	12	15	15	25
Earnings (loss) before income taxes	326	386	636	689
Income taxes (benefit)	64	151	145	277
Net income (loss)	262	235	491	412
Consolidated net income attributable to Southern Company	259	230	484	403
Condensed Statements of Cash Flows
Net income (loss)	262	235	491	412
Changes in certain current assets and liabilities:
Receivables			(153)	(58)
Other current assets			29	12
Accrued taxes			134	52
Other current liabilities			116	7
Condensed Balance Sheets
Unbilled revenues	174		174		162
Other accounts and notes receivable	41		41		55
Other current assets	11		11		5
Other current liabilities	143		143		59
Retained earnings	2,729		2,729		2,647
ALABAMA POWER CO | Balances Without Adoption of ASC 606
Condensed Statements of Income
Other revenues	60		114
Other operations and maintenance	391		767
Operating income (loss)	382		756
Other income (expense), net	10		11
GEORGIA POWER CO
Condensed Statements of Income
Other revenues	120	95	227	191
Other operations and maintenance	457	417	863	816
Operating income (loss)	(472)	621	41	1,105
Other income (expense), net	35	34	73	71
Earnings (loss) before income taxes	(539)	551	(94)	971
Income taxes (benefit)	(143)	199	(50)	355
Net income (loss)	(396)	352	(44)	616
Consolidated net income attributable to Southern Company	(396)	347	(44)	607
Condensed Statements of Cash Flows
Net income (loss)	(396)	352	(44)	616
Changes in certain current assets and liabilities:
Receivables			(103)	(150)
Other current assets			25	(18)
Accrued taxes			(89)	(194)
Other current liabilities			(26)	(6)
Condensed Balance Sheets
Unbilled revenues	276		276		255
Other accounts and notes receivable	81		81		76
Other current assets	23		23		14
Accrued taxes	230		230		344
Other current liabilities	205		205		198
Retained earnings	3,480		3,480		4,215
GEORGIA POWER CO | Balances Without Adoption of ASC 606
Condensed Statements of Income
Other revenues	97		189
Other operations and maintenance	437		828
Operating income (loss)	(475)		38
Other income (expense), net	38		76
Changes in certain current assets and liabilities:
Receivables			(75)
Other current assets			(3)
SOUTHERN Co GAS
Condensed Statements of Income
Natural gas revenues	710	684	2,341	2,205
Other revenues	24	32	55	62
Other operations and maintenance	238	214	514	470
Operating income (loss)	49	95	436	484
Other income (expense), net	3	4	15	10
Earnings (loss) before income taxes	24	80	407	468
Income taxes (benefit)	55	31	159	180
Net income (loss)	(31)	49	248	288
Consolidated net income attributable to Southern Company	(31)	49	248	288
Condensed Statements of Cash Flows
Net income (loss)	(31)	$ 49	248	288
Changes in certain current assets and liabilities:
Receivables			504	418
Other current assets			32	(12)
Accrued taxes			38	(8)
Other current liabilities			24	$ 25
Condensed Balance Sheets
Unbilled revenues	60		60		285
Other accounts and notes receivable	53		53		103
Other current assets	42		42		78
Accrued taxes	63		63		78
Accrued income taxes	86		86		40
Other current liabilities	143		143		159
Retained earnings	(202)		(202)		$ (212)
SOUTHERN Co GAS | Balances Without Adoption of ASC 606
Condensed Statements of Income
Natural gas revenues	717		2,334
Operating income (loss)	56		429
Earnings (loss) before income taxes	31		400
Income taxes (benefit)	57		157
Net income (loss)	(26)		243
Condensed Statements of Cash Flows
Net income (loss)	(26)		243
Changes in certain current assets and liabilities:
Accrued taxes			40
Other current liabilities			17
Condensed Balance Sheets
Accrued income taxes	84		84
Other current liabilities	150		150
Retained earnings	(207)		(207)
Accounting Standards Update 2014-09 | Effect of Change
Condensed Statements of Income
Natural gas revenues	(7)		7
Other revenues	2		3
Other operations and maintenance	13		23
Operating income (loss)	(18)		(13)
Other income (expense), net	11		20
Earnings (loss) before income taxes	(7)		7
Income taxes (benefit)	(2)		2
Net income (loss)	(5)		5
Consolidated net income attributable to Southern Company	(5)		5
Condensed Statements of Cash Flows
Net income (loss)	(5)		5
Changes in certain current assets and liabilities:
Receivables			(5)
Other current assets			5
Accrued taxes			(2)
Other current liabilities			7
Condensed Balance Sheets
Unbilled revenues	(55)		(55)
Other accounts and notes receivable	(1)		(1)
Other current assets	56		56
Accrued taxes	2		2
Other current liabilities	(7)		(7)
Retained earnings	5		5
Accounting Standards Update 2014-09 | ALABAMA POWER CO | Effect of Change
Condensed Statements of Income
Other revenues	9		17
Other operations and maintenance	11		21
Operating income (loss)	(2)		(4)
Other income (expense), net	2		4
Accounting Standards Update 2014-09 | GEORGIA POWER CO | Effect of Change
Condensed Statements of Income
Other revenues	23		38
Other operations and maintenance	20		35
Operating income (loss)	3		3
Other income (expense), net	(3)		(3)
Changes in certain current assets and liabilities:
Receivables			(28)
Other current assets			28
Accounting Standards Update 2014-09 | SOUTHERN Co GAS | Effect of Change
Condensed Statements of Income
Natural gas revenues	(7)		7
Operating income (loss)	(7)		7
Earnings (loss) before income taxes	(7)		7
Income taxes (benefit)	(2)		2
Net income (loss)	(5)		5
Condensed Statements of Cash Flows
Net income (loss)	(5)		5
Changes in certain current assets and liabilities:
Accrued taxes			(2)
Other current liabilities			7
Condensed Balance Sheets
Accrued income taxes	2		2
Other current liabilities	(7)		(7)
Retained earnings	$ 5		$ 5