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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Income and Other Taxes (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Southern Power |  |  |
Tax Credit Carryforward [Line Items] |  |  |
Percentage reduction in tax basis of assets | 50.00% |  |
Southern Company Gas |  |  |
Tax Credit Carryforward [Line Items] |  |  |
Excise taxes collected | $ 133 | $ 162 | $ 122
Included In Operating Expenses | Southern Company Gas |  |  |
Tax Credit Carryforward [Line Items] |  |  |
Excise taxes collected | $ 129 | $ 158 | $ 119

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- Definition The excise taxes collected by a public utility and reported in revenues if the amount of excise taxes is equal to 1 percent or more of such total. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(1)(e)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2 + Details
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