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RETIREMENT BENEFITS - Accumulated Benefit Obligation (Details) - Pension plans - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022
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Defined Benefit Plan Disclosure [Line Items] |  |
Total accumulated benefit obligation for the pension plans | $ 11,991 | $ 11,422
Alabama Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total accumulated benefit obligation for the pension plans | 2,746 | 2,601
Georgia Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total accumulated benefit obligation for the pension plans | 3,674 | 3,534
Mississippi Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total accumulated benefit obligation for the pension plans | 546 | 520
Southern Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total accumulated benefit obligation for the pension plans | 145 | 135
Southern Company Gas |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total accumulated benefit obligation for the pension plans | $ 808 | $ 801

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- Definition Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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