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Construction Amendment, Number Of Miles Of Pipe, Phase One

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments.

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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 current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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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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Contingencies - Other Matters (Details) $ in Millions	3 Months Ended			6 Months Ended		9 Months Ended
Contingencies - Other Matters (Details) $ in Millions	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Jan. 30, 2020 mi
Loss Contingencies [Line Items]
Tax expense	$ 372		$ 293			$ 550	$ 443
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Asset impairment charges						84	0
Tax expense	133		$ 3			224	$ 98
SOUTHERN Co GAS \| PennEast Pipeline
Loss Contingencies [Line Items]
Construction amendment, number of miles of pipe, phase one \| mi								68
Construction amendment, number of miles of pipe, phase two \| mi								50
Asset impairment charges	2			$ 84	$ 82	84
Asset impairment charges, net of tax	$ 2	$ 67		$ 67	$ 58
Tax expense						$ 7
Ownership percentage, equity method investment	20.00%			20.00%		20.00%
SOUTHERN Co GAS \| SNG
Loss Contingencies [Line Items]
Ownership percentage, equity method investment	50.00%			50.00%		50.00%
Commitment to fund contingent capital contribution	$ 150			$ 150		$ 150
SNG
Loss Contingencies [Line Items]
Debt maturing in June 2021	$ 300			$ 300		$ 300