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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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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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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 - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) state	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) state pipeline segment	Sep. 30, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of states in which entity operates \| state	3		3
Total operating revenues	$ 5,995	$ 6,159	$ 16,505	$ 18,158
Natural gas
Segment Reporting Information [Line Items]
Total operating revenues	498	492	2,661	2,806
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Total operating revenues	574	635	1,527	1,699
SOUTHERN POWER CO \| Wholesale revenues, affiliates
Segment Reporting Information [Line Items]
Total operating revenues	$ 116	134	$ 320	326
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Number of states in which entity operates \| state	4		4
Total operating revenues	$ 498	492	$ 2,661	2,861
Number of reportable segments \| segment			4
SOUTHERN Co GAS \| Pipeline
Segment Reporting Information [Line Items]
Number of pipeline construction projects \| pipeline			2
SOUTHERN Co GAS \| SNG
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	50.00%		50.00%
SOUTHERN Co GAS \| Dalton Pipeline
Segment Reporting Information [Line Items]
Ownership percentage, equity method investment	50.00%		50.00%
SOUTHERN Co GAS \| Natural gas
Segment Reporting Information [Line Items]
Total operating revenues	$ 498	487	$ 2,661	2,829
SOUTHERN Co GAS \| Traditional Electric Operating Companies \| Natural gas
Segment Reporting Information [Line Items]
Total operating revenues	9	14	13	22
SOUTHERN Co GAS \| SOUTHERN POWER CO \| Natural gas
Segment Reporting Information [Line Items]
Total operating revenues	$ 20	$ 38	$ 53	$ 96