CONTINGENCIES, COMMITMENTS, AND GUARANTEES - GAS Commitments (Details) MMBTU in Millions, $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($) MMBTU
Pipeline Charges, Storage Capacity, and Gas Supply
Debt maturing in June 2021	$ 3,506
Southern Company Gas
Long-term Purchase Commitment [Line Items]
Natural gas pipeline capacity \| MMBTU	31
Long-term purchase commitment amount	$ 72
Pipeline Charges, Storage Capacity, and Gas Supply
Debt maturing in June 2021	$ 330
Southern Company Gas \| SNG
Pipeline Charges, Storage Capacity, and Gas Supply
Ownership percentage, equity method investment	50.00%
Commitment to fund contingent capital contribution	$ 150
SNG
Pipeline Charges, Storage Capacity, and Gas Supply
Debt maturing in June 2021	300
Pipeline Charges, Storage Capacity, and Gas Supply \| Southern Company Gas
Pipeline Charges, Storage Capacity, and Gas Supply
2021	719
2022	529
2023	441
2024	311
2025	285
Thereafter	1,035
Total	$ 3,320

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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.

+ References

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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 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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
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-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690

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The minimum amount the entity agreed to spend under the long-term purchase commitment.

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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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Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid in fifth 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).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121559207&loc=d3e25336-109308

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Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid 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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Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid in fourth 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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Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid in second 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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Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid in third 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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Amount of the unrecorded obligation to transfer funds in the future for fixed or minimum amounts or quantities of goods or services at fixed or minimum prices (for example, as in take-or-pay contracts or throughput contracts).

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Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid after fifth 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).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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