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EBIT represents earnings before interest and taxes, a non-GAAP measure that includes operating income and other income and excludes financing costs, including interest and debt and income tax expense

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Loss on Coal-Fired Power Plant Unit

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Number of Natural Gas Distribution Utilities

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- Definition

Pre-Tax Charge To Income

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Affiliated revenues from sales of energy supplied by one producer or marketer to another for eventual resale to consumers.

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Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(12))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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-Name Accounting Standards Codification
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-Section S99
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The aggregate cost of goods produced and sold and services rendered during the reporting period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-URI http://asc.fasb.org/extlink&oid=64863997&loc=d3e1377-109256

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The number of states the entity operates in as of the balance sheet date.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Segment and Related Information - Financial Data for Business Segments (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($) state segment	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of states in which entity operates \| state	4
Operating revenues	$ 5,771	$ 3,992
Segment net income (loss)	658	489
Total assets	109,760		$ 109,697
Kemper IGCC [Member]
Segment Reporting Information [Line Items]
Pre-tax charge to income	108	53
After tax charge to income	67	33
Plant Scherer Unit 3 [Member]
Segment Reporting Information [Line Items]
After tax charge to income	20
Loss on Plant Scherer Unit 3	33
Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	4,131	3,981
Segment net income (loss)	502	515
Total assets	87,067		86,994
Intersegment Eliminations [Member] \| Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	(105)	(103)
Segment net income (loss)	0	0
Total assets	(306)		(316)
Consolidation Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(43)	(36)
Segment net income (loss)	1	(3)
Total assets	(1,564)		(1,624)
Traditional Operating Companies [Member] \| Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,786	3,769
Segment net income (loss)	432	465
Total assets	72,692		72,141
Southern Power [Member] \| Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	450	315
Segment net income (loss)	70	50
Total assets	14,681		15,169
Southern Company Gas [Member] \| Natural Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,560
Segment net income (loss)	239
Total assets	21,683		21,853
All Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	123	47
Segment net income (loss)	(84)	(23)
Total assets	2,574		2,474
Gulf Power [Member]
Segment Reporting Information [Line Items]
Wholesale revenues, affiliates	37	21
Operating revenues	350	335
Segment net income (loss)	18	29
Total assets	4,767		4,822
Loss on Plant Scherer Unit 3	$ 33	0
Southern Company Gas [Member]
Segment Reporting Information [Line Items]
Number of reportable segments \| segment	7
Operating revenues	$ 1,560
Segment net income (loss)	239
Total assets	21,683		21,853
Southern Company Gas [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,624
Segment net income (loss)	231
Total assets	23,700		24,875
Southern Company Gas [Member] \| Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(66)
Segment net income (loss)	0
Total assets	(12,877)		(14,167)
Southern Company Gas [Member] \| Gas Distribution Operations [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,180
Segment net income (loss)	117
Total assets	18,201		19,453
Southern Company Gas [Member] \| Gas Marketing Services [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	288
Segment net income (loss)	31
Total assets	2,118		2,084
Southern Company Gas [Member] \| Wholesale Gas Services [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	131
Segment net income (loss)	68
Total assets	1,018		1,127
Cost of Revenue	1,844
Southern Company Gas [Member] \| Gas Midstream Operations [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	25
Segment net income (loss)	15
Total assets	2,363		2,211
Southern Company Gas [Member] \| All Other [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	2
Segment net income (loss)	8
Total assets	10,860		11,145
Southern Power [Member]
Segment Reporting Information [Line Items]
Wholesale revenues, affiliates	100	97
Operating revenues	450	315
Segment net income (loss)	70	50
Total assets	14,681		$ 15,169
Predecessor [Member] \| Southern Company Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		1,334
Segment net income (loss)		182
EBIT		352
Predecessor [Member] \| Southern Company Gas [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		1,392
EBIT		358
Predecessor [Member] \| Southern Company Gas [Member] \| Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues		(60)
EBIT		(1)
Predecessor [Member] \| Southern Company Gas [Member] \| Gas Distribution Operations [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		1,028
EBIT		235
Predecessor [Member] \| Southern Company Gas [Member] \| Gas Marketing Services [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		286
EBIT		80
Predecessor [Member] \| Southern Company Gas [Member] \| Wholesale Gas Services [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		63
EBIT		44
Cost of Revenue		1,461
Predecessor [Member] \| Southern Company Gas [Member] \| Gas Midstream Operations [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		15
EBIT		(1)
Predecessor [Member] \| Southern Company Gas [Member] \| All Other [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		2
EBIT		(5)
Third Party Gross Revenues [Member] \| Southern Company Gas [Member] \| Wholesale Gas Services [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,839
Third Party Gross Revenues [Member] \| Predecessor [Member] \| Southern Company Gas [Member] \| Wholesale Gas Services [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		1,443
Intercompany Revenues [Member] \| Southern Company Gas [Member] \| Wholesale Gas Services [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	136
Intercompany Revenues [Member] \| Predecessor [Member] \| Southern Company Gas [Member] \| Wholesale Gas Services [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		81
Total Gross Revenues [Member] \| Southern Company Gas [Member] \| Wholesale Gas Services [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 1,975
Total Gross Revenues [Member] \| Predecessor [Member] \| Southern Company Gas [Member] \| Wholesale Gas Services [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		$ 1,524