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Disposal Group, Not Discontinued Operations, Gain (Loss) On Disposal, Tax

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Number Of Natural Gas Distributions Utilities Sold

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Pipeline Infrastructure

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Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)

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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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This element represents the aggregate cost of investments accounted for under the equity method of accounting.

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Difference between amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee.

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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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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

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The cash inflow associated with the amount received from the sale of a portion of the company's business, for example a segment, division, branch or other business, during the period.

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The cash inflow to dispose of long-lived, physical assets and mineral interests in oil and gas properties used for normal oil and gas operations.

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Acquisitions and Dispositions - GAS Acquisitions and Dispositions Narrative (Details)					1 Months Ended	3 Months Ended				6 Months Ended	12 Months Ended
	Jul. 29, 2018 USD ($)	Jul. 01, 2018 USD ($) utility	Jun. 04, 2018 USD ($)	Mar. 31, 2017 USD ($)	Jul. 31, 2018 utility	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2016 USD ($) mi	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) mi
Business Acquisition [Line Items]
Payments to acquire equity method investments											$ 114,000,000	$ 152,000,000	$ 1,444,000,000
Goodwill impairment						$ 0					42,000,000
Number of natural gas distribution utilities sold \| utility					3
Southern Company Gas
Business Acquisition [Line Items]
Payments to acquire equity method investments										$ 1,444,000,000	110,000,000	145,000,000
Goodwill impairment						$ 0			$ 42,000,000	$ 0	$ 42,000,000	0
Number of natural gas distribution utilities sold \| utility					3
Southern Company Gas \| Southern Natural Gas Company, LLC
Business Acquisition [Line Items]
Pipeline infrastructure \| mi										7,000			7,000
Southern Company Gas \| Southern Natural Gas Company, LLC
Business Acquisition [Line Items]
Ownership percentage, equity method investment						50.00%					50.00%
Payments to acquire equity method investments				$ 50,000,000
Tax Cuts And Jobs Act Of 2017, incomplete accounting, provisional income tax expense (benefit)												$ 104,000,000
Southern Company Gas \| Southern Natural Gas Company, LLC \| Southern Natural Gas Company, LLC
Business Acquisition [Line Items]
Ownership percentage, equity method investment										50.00%			50.00%
Equity method investment, aggregate cost										$ 1,400,000,000			$ 1,400,000,000
Equity method investment, difference between carrying amount and underlying equity										$ 700,000,000			$ 700,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Southern Company Gas
Business Acquisition [Line Items]
Gain (loss) on dispositions, after tax						$ (15,000,000)	$ 40,000,000	$ (76,000,000)
Pivotal Home Solutions \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Southern Company Gas
Business Acquisition [Line Items]
Cash proceeds from sale of business			$ 365,000,000
Gain (loss) on dispositions, after tax			(67,000,000)
Tax on sale of business			$ 34,000,000
Goodwill impairment									$ 42,000,000		$ 42,000,000
Elizabethtown Gas and Elkton Gas \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Southern Company Gas
Business Acquisition [Line Items]
Gain (loss) on dispositions, after tax		$ 0
Tax on sale of business		$ 205,000,000
Number of natural gas distribution utilities sold \| utility		2
Florida City Gas \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Southern Company Gas
Business Acquisition [Line Items]
Cash proceeds from sale of business	$ 587,000,000
Gain (loss) on dispositions, after tax	16,000,000
Tax on sale of business	$ 103,000,000
Subsidiaries
Business Acquisition [Line Items]
Proceeds from sale of oil and gas property and equipment		$ 1,700,000,000