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RETIREMENT BENEFITS - Amounts Recognized in Balance Sheets and Amounts in AOCI (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Other regulatory assets, deferred | $ 6,264 | $ 5,918
Other current liabilities | (1,029) | (787)
Employee benefit obligations | (1,115) | (1,238)
Other regulatory liabilities, deferred | (715) | (733)
Regulatory asset | 66 | 216
Pension plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension costs | 2,079 | 2,290
Other regulatory assets, deferred | 2,960 | 2,455
Other current liabilities | (64) | (56)
Employee benefit obligations | (649) | (618)
Other regulatory liabilities, deferred | (47) | (85)
AOCI | 79 | 24
Other Postretirement Benefits Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension and other postretirement benefit costs | 0 | 0
Other regulatory assets, deferred | 23 | 34
Other current liabilities | (6) | (6)
Employee benefit obligations | (285) | (437)
Other regulatory liabilities, deferred | (231) | (170)
AOCI | (9) | (4)
Alabama Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension and other postretirement benefit costs | 659 | 657
Other regulatory assets, deferred | 1,858 | 2,107
Other current liabilities | (191) | (91)
Employee benefit obligations | (155) | (145)
Other regulatory liabilities, deferred | (291) | (315)
Regulatory asset | 76 | 97
Alabama Power | Pension plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension costs | 585 | 629
Other regulatory assets, deferred | 821 | 679
Other current liabilities | (11) | (10)
Employee benefit obligations | (106) | (98)
Other regulatory liabilities, deferred | 0 | 0
AOCI | 0 | 0
Alabama Power | Other Postretirement Benefits Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension and other postretirement benefit costs | 74 | 28
Other regulatory assets, deferred | 0 | 0
Other current liabilities | 0 | 0
Employee benefit obligations | 0 | 0
Other regulatory liabilities, deferred | (48) | (21)
AOCI | 0 | 0
Georgia Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Other regulatory assets, deferred | 2,890 | 2,522
Other current liabilities | (365) | (286)
Employee benefit obligations | (248) | (318)
Regulatory asset |  | 83
Georgia Power | Pension plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension costs | 706 | 738
Other regulatory assets, deferred | 1,051 | 887
Other current liabilities | (13) | (12)
Employee benefit obligations | (131) | (121)
Other regulatory liabilities, deferred | 0 | 0
AOCI | 0 | 0
Georgia Power | Other Postretirement Benefits Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension and other postretirement benefit costs | 0 | 0
Other regulatory assets, deferred | 11 | 19
Other current liabilities | 0 | 0
Employee benefit obligations | (79) | (146)
Other regulatory liabilities, deferred | (85) | (58)
AOCI | 0 | 0
Mississippi Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Other regulatory assets, deferred | 285 | 249
Other current liabilities | (90) | (85)
Employee benefit obligations | (67) | (69)
Other regulatory liabilities, deferred | (92) | (96)
Regulatory asset | 44 | 36
Mississippi Power | Pension plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension costs | 99 | 108
Other regulatory assets, deferred | 152 | 123
Other current liabilities | (2) | (2)
Employee benefit obligations | (27) | (26)
Other regulatory liabilities, deferred | 0 | 0
AOCI | 0 | 0
Mississippi Power | Other Postretirement Benefits Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension and other postretirement benefit costs | 0 | 0
Other regulatory assets, deferred | 0 | 0
Other current liabilities | 0 | 0
Employee benefit obligations | (32) | (35)
Other regulatory liabilities, deferred | (10) | (9)
AOCI | 0 | 0
Southern Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Other current liabilities | (97) | (83)
Southern Power | Pension plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension costs | 31 | 37
Other regulatory assets, deferred | 0 | 0
Other current liabilities | (2) | (2)
Employee benefit obligations | (21) | (20)
Other regulatory liabilities, deferred | 0 | 0
AOCI | 20 | 11
Southern Power | Other Postretirement Benefits Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension and other postretirement benefit costs | 0 | 0
Other regulatory assets, deferred | 0 | 0
Other current liabilities | (1) | (1)
Employee benefit obligations | (8) | (8)
Other regulatory liabilities, deferred | 0 | 0
AOCI | 1 | 0
Southern Company Gas |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Other regulatory assets, deferred | 504 | 497
Other current liabilities | (232) | (254)
Employee benefit obligations | (110) | (120)
Southern Company Gas | Pension plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension costs | 158 | 183
Other regulatory assets, deferred | 143 | 111
Other current liabilities | (3) | (3)
Employee benefit obligations | (58) | (42)
Other regulatory liabilities, deferred | 0 | 0
AOCI | (45) | (75)
Regulatory asset | 173 | 190
Southern Company Gas | Other Postretirement Benefits Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension and other postretirement benefit costs | 0 | 0
Other regulatory assets, deferred | 0 | 0
Other current liabilities | 0 | 0
Employee benefit obligations | (44) | (66)
Other regulatory liabilities, deferred | (68) | (58)
AOCI | (10) | (2)
Regulatory asset | $ 24 | $ 32

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