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RETIREMENT BENEFITS - Accumulated Benefit Obligation (Details) - Pension plans - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020
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Defined Benefit Plan Disclosure [Line Items] |  |
Total accumulated benefit obligation for the pension plans | $ 14,687 | $ 14,922
Alabama Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total accumulated benefit obligation for the pension plans | 3,362 | 3,414
Georgia Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total accumulated benefit obligation for the pension plans | 4,562 | 4,657
Mississippi Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total accumulated benefit obligation for the pension plans | 672 | 683
Southern Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total accumulated benefit obligation for the pension plans | 178 | 175
Southern Company Gas |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total accumulated benefit obligation for the pension plans | $ 1,030 | $ 1,072

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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 -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 + Details
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