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RETIREMENT BENEFITS - 401K Plan Matching Contributions (Details) - Employee Savings Plan - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined contribution plan, cost | $ 131 | $ 124 | $ 119
Alabama Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined contribution plan, cost | 28 | 26 | 26
Georgia Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined contribution plan, cost | 31 | 29 | 28
Mississippi Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined contribution plan, cost | 5 | 5 | 5
Southern Power |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined contribution plan, cost | 3 | 3 | 2
Southern Company Gas |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined contribution plan, cost | $ 18 | $ 17 | $ 16

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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 70 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480794/715-70-50-1 + Details
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