Introduction - ASC 606 (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Condensed Statements of Income
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	$ 1,607	$ 1,530
Other revenues	413	141
Other operations and maintenance	1,451	1,383
Operating income	1,376	1,252
Other income (expense), net	60	48
Earnings before income taxes	1,049	980
Income taxes	113	315
Net income	936	665
Consolidated net income attributable to Southern Company	$ 938	$ 658
Basic earnings per share (in dollars per share)	$ 0.93	$ 0.66
Diluted earnings per share (in dollars per share)	$ 0.92	$ 0.66
Condensed Consolidated Statements of Cash Flow
Net income	$ 936	$ 665
Changes in certain current assets and liabilities:
Receivables	197	310
Other current assets	7	(31)
Accrued taxes	(79)	(212)
Other current liabilities	81	(48)
Condensed Balance Sheet
Unbilled revenues	777		$ 810
Other accounts and notes receivable	703		698
Other current assets	286		211
Accrued taxes	368		636
Other current liabilities	923		874
Retained earnings	9,257		8,885
Balances Without Adoption of ASC 606
Condensed Statements of Income
Net income	$ 926
Basic earnings per share (in dollars per share)	$ 0.92
Diluted earnings per share (in dollars per share)	$ 0.91
Condensed Consolidated Statements of Cash Flow
Net income	$ 926
Changes in certain current assets and liabilities:
Receivables	211
Other current assets	7
Accrued taxes	(75)
Other current liabilities	67
Condensed Balance Sheet
Unbilled revenues	822
Other accounts and notes receivable	709
Other current assets	235
Accrued taxes	364
Other current liabilities	937
Retained earnings	9,247
ALABAMA POWER CO
Condensed Statements of Income
Other revenues	63	56
Other operations and maintenance	387	384
Operating income	372	361
Other income (expense), net	5	10
Earnings before income taxes	311	304
Income taxes	82	126
Net income	229	178
Consolidated net income attributable to Southern Company	225	174
Condensed Consolidated Statements of Cash Flow
Net income	229	178
Changes in certain current assets and liabilities:
Other current assets	19	39
Accrued taxes	57	77
Other current liabilities	45	(9)
Condensed Balance Sheet
Unbilled revenues	131		162
Other accounts and notes receivable	36		55
Other current assets	3		5
Accrued taxes	77		54
Other current liabilities	57		56
Retained earnings	2,670		2,647
ALABAMA POWER CO | Balances Without Adoption of ASC 606
Condensed Statements of Income
Other revenues	55
Other operations and maintenance	377
Operating income	374
Other income (expense), net	3
GEORGIA POWER CO
Condensed Statements of Income
Other revenues	109	96
Other operations and maintenance	408	399
Operating income	513	483
Other income (expense), net	38	38
Earnings before income taxes	445	420
Income taxes	93	156
Net income	352	264
Consolidated net income attributable to Southern Company	352	260
Condensed Consolidated Statements of Cash Flow
Net income	352	264
Changes in certain current assets and liabilities:
Receivables	135	142
Other current assets	9	(16)
Accrued taxes	(191)	(235)
Other current liabilities	(3)	2
Condensed Balance Sheet
Unbilled revenues	189		255
Other accounts and notes receivable	77		76
Other current assets	39		14
Other current liabilities	215		198
Retained earnings	4,228		4,215
Accrued income taxes	129		344
GEORGIA POWER CO | Balances Without Adoption of ASC 606
Condensed Statements of Income
Other revenues	94
Other operations and maintenance	394
Operating income	512
Other income (expense), net	39
Changes in certain current assets and liabilities:
Receivables	145
Other current assets	(1)
Condensed Balance Sheet
Unbilled revenues	202
Other accounts and notes receivable	83
Other current assets	20
SOUTHERN Co GAS
Condensed Statements of Income
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	1,631	1,521
Other revenues	32	30
Other operations and maintenance	276	255
Operating income	388	389
Other income (expense), net	12	7
Earnings before income taxes	383	389
Income taxes	104	150
Net income	279	239
Consolidated net income attributable to Southern Company	279	239
Condensed Consolidated Statements of Cash Flow
Net income	279	239
Changes in certain current assets and liabilities:
Receivables	175	115
Other current assets	14	19
Accrued taxes	28	19
Other current liabilities	48	49
Condensed Balance Sheet
Unbilled revenues	210		285
Other accounts and notes receivable	51		103
Other current assets	51		78
Accrued taxes	76		78
Other current liabilities	143		159
Retained earnings	(55)		(212)
Accrued income taxes	77		$ 40
SOUTHERN Co GAS | Balances Without Adoption of ASC 606
Condensed Statements of Income
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	1,617
Operating income	374
Earnings before income taxes	369
Income taxes	100
Net income	269
Condensed Consolidated Statements of Cash Flow
Net income	269
Changes in certain current assets and liabilities:
Accrued taxes	32
Other current liabilities	34
Condensed Balance Sheet
Other current liabilities	157
Retained earnings	(65)
Accrued income taxes	73
Operating Segments | SOUTHERN Co GAS
Condensed Statements of Income
Consolidated net income attributable to Southern Company	289	$ 231
SOUTHERN Co GAS | Operating Segments | SOUTHERN Co GAS
Condensed Statements of Income
Consolidated net income attributable to Southern Company	279
Southern Company
Condensed Statements of Income
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	1,607
Other revenues	413
Southern Company | Balances Without Adoption of ASC 606
Condensed Statements of Income
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	1,593
Other revenues	412
Other operations and maintenance	1,441
Operating income	1,371
Other income (expense), net	51
Earnings before income taxes	1,035
Income taxes	109
Net income	926
Consolidated net income attributable to Southern Company	928
Condensed Consolidated Statements of Cash Flow
Net income	926
Accounting Standards Update 2014-09 | Effect of Change
Condensed Statements of Income
Net income	$ 10
Basic earnings per share (in dollars per share)	$ 0.01
Diluted earnings per share (in dollars per share)	$ 0.01
Condensed Consolidated Statements of Cash Flow
Net income	$ 10
Changes in certain current assets and liabilities:
Receivables	(14)
Other current assets	(14)
Accrued taxes	(4)
Other current liabilities	14
Condensed Balance Sheet
Unbilled revenues	(45)
Other accounts and notes receivable	(6)
Other current assets	51
Accrued taxes	4
Other current liabilities	(14)
Retained earnings	10
Accounting Standards Update 2014-09 | ALABAMA POWER CO | Effect of Change
Condensed Statements of Income
Other revenues	8
Other operations and maintenance	10
Operating income	(2)
Other income (expense), net	2
Accounting Standards Update 2014-09 | GEORGIA POWER CO | Effect of Change
Condensed Statements of Income
Other revenues	15
Other operations and maintenance	14
Operating income	1
Other income (expense), net	(1)
Changes in certain current assets and liabilities:
Receivables	(10)
Other current assets	10
Condensed Balance Sheet
Unbilled revenues	(13)
Other accounts and notes receivable	(6)
Other current assets	19
Accounting Standards Update 2014-09 | SOUTHERN Co GAS | Effect of Change
Condensed Statements of Income
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	14
Operating income	14
Earnings before income taxes	14
Income taxes	4
Net income	10
Condensed Consolidated Statements of Cash Flow
Net income	10
Changes in certain current assets and liabilities:
Accrued taxes	(4)
Other current liabilities	14
Condensed Balance Sheet
Other current liabilities	(14)
Retained earnings	10
Accrued income taxes	4
Accounting Standards Update 2014-09 | Southern Company | Effect of Change
Condensed Statements of Income
Natural gas revenues (includes alternative revenue programs of $(24) and $9, respectively)	14
Other revenues	1
Other operations and maintenance	10
Operating income	5
Other income (expense), net	9
Earnings before income taxes	14
Income taxes	4
Net income	10
Consolidated net income attributable to Southern Company	10
Condensed Consolidated Statements of Cash Flow
Net income	$ 10