Introduction - ASC 606 (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Condensed Statements of Income
Total operating revenues	$ 6,159	$ 6,201	$ 18,158	$ 17,403
Other operations and maintenance	1,404	1,341	4,217	4,100
Operating income (loss)	2,174	1,991	3,613	1,594
Other income (expense), net	57	65	195	165
Earnings (loss) before income taxes	1,845	1,699	2,629	744
Income taxes (benefit)	623	590	598	317
Consolidated net income (loss)	1,222	1,109	2,031	427
Consolidated net income (loss) attributable to Southern Company	1,164	1,069	1,948	347
Condensed Statements of Cash Flows
Net income (loss)	1,222	1,109	2,031	427
Changes in certain current assets and liabilities:
Receivables			37	423
Other current assets			(90)	(66)
Other current liabilities			(67)	(129)
Condensed Balance Sheets
Unbilled revenues	738		738		$ 810
Other accounts and notes receivable	690		690		698
Other current assets	232		232		199
Other current liabilities	763		763		874
Retained earnings (accumulated deficit)	9,048		9,048		8,885
Balances Without Adoption of ASC 606
Condensed Statements of Income
Other operations and maintenance	1,387		4,178
Operating income (loss)	2,195		3,647
Other income (expense), net	41		160
Earnings (loss) before income taxes	1,850		2,628
Income taxes (benefit)	624		598
Consolidated net income (loss)	1,226		2,030
Consolidated net income (loss) attributable to Southern Company	1,168		1,947
Condensed Statements of Cash Flows
Net income (loss)	1,226		2,030
Changes in certain current assets and liabilities:
Receivables			27
Other current assets			(80)
Other current liabilities			(68)
Condensed Balance Sheets
Unbilled revenues	776		776
Other accounts and notes receivable	691		691
Other current assets	193		193
Other current liabilities	764		764
Retained earnings (accumulated deficit)	9,047		9,047
ALABAMA POWER CO
Condensed Statements of Income
Total operating revenues	1,740	1,740	4,716	4,606
Other operations and maintenance	401	406	1,191	1,177
Operating income (loss)	561	601	1,313	1,403
Other income (expense), net	9	10	24	35
Earnings (loss) before income taxes	504	546	1,140	1,236
Income taxes (benefit)	127	216	272	493
Consolidated net income (loss)	377	330	868	743
Consolidated net income (loss) attributable to Southern Company	373	325	857	729
Condensed Statements of Cash Flows
Net income (loss)	377	330	868	743
Changes in certain current assets and liabilities:
Receivables			(207)	(163)
Other current assets			66	33
Other current liabilities			60	7
Condensed Balance Sheets
Unbilled revenues	159		159		162
Other accounts and notes receivable	54		54		55
Other current assets	8		8		5
Other current liabilities	46		46		52
Retained earnings (accumulated deficit)	2,902		2,902		2,647
ALABAMA POWER CO | Balances Without Adoption of ASC 606
Condensed Statements of Income
Other operations and maintenance	390		1,159
Operating income (loss)	563		1,319
Other income (expense), net	7		18
GEORGIA POWER CO
Condensed Statements of Income
Total operating revenues	2,593	2,546	6,601	6,426
Other operations and maintenance	460	430	1,325	1,248
Operating income (loss)	991	1,017	1,032	2,121
Other income (expense), net	30	22	104	95
Earnings (loss) before income taxes	926	934	833	1,906
Income taxes (benefit)	262	350	212	705
Consolidated net income (loss)	664	584	621	1,201
Consolidated net income (loss) attributable to Southern Company	664	580	621	1,188
Condensed Statements of Cash Flows
Net income (loss)	664	584	621	1,201
Changes in certain current assets and liabilities:
Receivables			(205)	(254)
Other current assets			(36)	(24)
Other current liabilities			(111)	(11)
Condensed Balance Sheets
Unbilled revenues	245		245		255
Other accounts and notes receivable	96		96		76
Other current assets	91		91		14
Other current liabilities	180		180		198
Retained earnings (accumulated deficit)	3,792		3,792		4,215
GEORGIA POWER CO | Balances Without Adoption of ASC 606
Condensed Statements of Income
Other operations and maintenance	437		1,268
Operating income (loss)	990		1,027
Other income (expense), net	31		109
Changes in certain current assets and liabilities:
Receivables			(242)
Other current assets			1
Condensed Balance Sheets
Unbilled revenues	310		310
Other accounts and notes receivable	97		97
Other current assets	25		25
SOUTHERN Co GAS
Condensed Statements of Income
Total operating revenues	492	565	2,861	2,841
Other operations and maintenance	216	206	730	675
Operating income (loss)	374	67	810	551
Other income (expense), net	6	19	21	30
Earnings (loss) before income taxes	362	67	769	536
Income taxes (benefit)	316	52	475	233
Consolidated net income (loss)	46	15	294	303
Consolidated net income (loss) attributable to Southern Company	46	15	294	303
Condensed Statements of Cash Flows
Net income (loss)	46	15	294	303
Changes in certain current assets and liabilities:
Receivables			445	531
Other current assets			21	(42)
Other current liabilities			35	8
Condensed Balance Sheets
Unbilled revenues	58		58		285
Other accounts and notes receivable	110		110		91
Other current assets	88		88		78
Other current liabilities	122		122		159
Retained earnings (accumulated deficit)	(273)		(273)		$ (212)
SOUTHERN Co GAS | Balances Without Adoption of ASC 606
Condensed Statements of Income
Operating income (loss)	379		809
Earnings (loss) before income taxes	367		768
Income taxes (benefit)	317		475
Consolidated net income (loss)	50		293
Condensed Statements of Cash Flows
Net income (loss)	50		293
Changes in certain current assets and liabilities:
Other current liabilities			34
Condensed Balance Sheets
Other current liabilities	123		123
Retained earnings (accumulated deficit)	(274)		(274)
SOUTHERN Co GAS
Condensed Statements of Income
Total operating revenues	492	565	2,861	2,841
Accounting Standards Update 2014-09 | Effect of Change
Condensed Statements of Income
Other operations and maintenance	17		39
Operating income (loss)	(21)		(34)
Other income (expense), net	16		35
Earnings (loss) before income taxes	(5)		1
Income taxes (benefit)	(1)		0
Consolidated net income (loss)	(4)		1
Consolidated net income (loss) attributable to Southern Company	(4)		1
Condensed Statements of Cash Flows
Net income (loss)	(4)		1
Changes in certain current assets and liabilities:
Receivables			10
Other current assets			(10)
Other current liabilities			1
Condensed Balance Sheets
Unbilled revenues	(38)		(38)
Other accounts and notes receivable	(1)		(1)
Other current assets	39		39
Other current liabilities	(1)		(1)
Retained earnings (accumulated deficit)	1		1
Accounting Standards Update 2014-09 | ALABAMA POWER CO | Effect of Change
Condensed Statements of Income
Other operations and maintenance	11		32
Operating income (loss)	(2)		(6)
Other income (expense), net	2		6
Accounting Standards Update 2014-09 | GEORGIA POWER CO | Effect of Change
Condensed Statements of Income
Other operations and maintenance	23		57
Operating income (loss)	1		5
Other income (expense), net	(1)		(5)
Changes in certain current assets and liabilities:
Receivables			37
Other current assets			(37)
Condensed Balance Sheets
Unbilled revenues	(65)		(65)
Other accounts and notes receivable	(1)		(1)
Other current assets	66		66
Accounting Standards Update 2014-09 | SOUTHERN Co GAS | Effect of Change
Condensed Statements of Income
Operating income (loss)	(5)		1
Earnings (loss) before income taxes	(5)		1
Income taxes (benefit)	(1)		0
Consolidated net income (loss)	(4)		1
Condensed Statements of Cash Flows
Net income (loss)	(4)		1
Changes in certain current assets and liabilities:
Other current liabilities			1
Condensed Balance Sheets
Other current liabilities	(1)		(1)
Retained earnings (accumulated deficit)	1		1
Natural gas
Condensed Statements of Income
Total operating revenues	492	532	2,806	2,746
Natural gas | Balances Without Adoption of ASC 606
Condensed Statements of Income
Total operating revenues	497		2,805
Natural gas | SOUTHERN Co GAS
Condensed Statements of Income
Total operating revenues	487	532	2,829	2,737
Natural gas | SOUTHERN Co GAS | Balances Without Adoption of ASC 606
Condensed Statements of Income
Total operating revenues	492		2,828
Natural gas | Accounting Standards Update 2014-09 | Effect of Change
Condensed Statements of Income
Total operating revenues	(5)		1
Natural gas | Accounting Standards Update 2014-09 | SOUTHERN Co GAS | Effect of Change
Condensed Statements of Income
Total operating revenues	(5)		1
Other revenues
Condensed Statements of Income
Total operating revenues	199	168	1,007	494
Other revenues | Balances Without Adoption of ASC 606
Condensed Statements of Income
Total operating revenues	198		1,003
Other revenues | ALABAMA POWER CO
Condensed Statements of Income
Total operating revenues	68	50	199	158
Other revenues | ALABAMA POWER CO | Balances Without Adoption of ASC 606
Condensed Statements of Income
Total operating revenues	59		173
Other revenues | GEORGIA POWER CO
Condensed Statements of Income
Total operating revenues	121	93	349	284
Other revenues | GEORGIA POWER CO | Balances Without Adoption of ASC 606
Condensed Statements of Income
Total operating revenues	97		287
Other revenues | SOUTHERN Co GAS
Condensed Statements of Income
Total operating revenues	0	$ 33	55	$ 95
Other revenues | Accounting Standards Update 2014-09 | Effect of Change
Condensed Statements of Income
Total operating revenues	1		4
Other revenues | Accounting Standards Update 2014-09 | ALABAMA POWER CO | Effect of Change
Condensed Statements of Income
Total operating revenues	9		26
Other revenues | Accounting Standards Update 2014-09 | GEORGIA POWER CO | Effect of Change
Condensed Statements of Income
Total operating revenues	$ 24		$ 62