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RETIREMENT BENEFITS - Amounts Recognized in Balance Sheets and Amounts in AOCI (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Other regulatory assets, deferred | $ 5,577 | $ 7,198
Other current liabilities | (872) | (968)
Employee benefit obligations | (1,550) | (2,213)
Other regulatory liabilities, deferred | (485) | (251)
Pension plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension costs | 1,657 | 0
Other regulatory assets, deferred | 2,920 | 4,655
Other current liabilities | (55) | (52)
Employee benefit obligations | (759) | (1,227)
Other regulatory liabilities, deferred | (119) | (34)
AOCI | 100 | 245
Other postretirement benefit plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension and other postretirement benefit costs | 0 |
Other regulatory assets, deferred | 97 | 137
Other current liabilities | (5) | (5)
Employee benefit obligations | (593) | (785)
Other regulatory liabilities, deferred | (171) | (86)
AOCI | 0 | 8
Alabama Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension and other postretirement benefit costs | 513 | 0
Other regulatory assets, deferred | 1,807 | 2,162
Other current liabilities | (125) | (107)
Employee benefit obligations | (171) | (214)
Other regulatory liabilities, deferred | (210) | (124)
Alabama Power | Pension plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension costs | 464 | 0
Other regulatory assets, deferred | 809 | 1,286
Other current liabilities | (9) | (9)
Employee benefit obligations | (120) | (161)
Other regulatory liabilities, deferred | 0 | 0
AOCI | 0 | 0
Alabama Power | Other postretirement benefit plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension and other postretirement benefit costs | 49 |
Other regulatory assets, deferred | 0 | 0
Other current liabilities | 0 | 0
Employee benefit obligations | 0 | (5)
Other regulatory liabilities, deferred | (62) | (21)
AOCI | 0 | 0
Georgia Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Other regulatory assets, deferred | 1,964 | 2,692
Other current liabilities | (254) | (254)
Employee benefit obligations | (402) | (586)
Georgia Power | Pension plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension costs | 563 | 0
Other regulatory assets, deferred | 971 | 1,598
Other current liabilities | (12) | (10)
Employee benefit obligations | (148) | (273)
Other regulatory liabilities, deferred | 0 | 0
AOCI | 0 | 0
Georgia Power | Other postretirement benefit plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension and other postretirement benefit costs | 0 |
Other regulatory assets, deferred | 30 | 47
Other current liabilities | 0 | 0
Employee benefit obligations | (206) | (272)
Other regulatory liabilities, deferred | (40) | 0
AOCI | 0 | 0
Mississippi Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension costs | 79 | 0
Other regulatory assets, deferred | 317 | 388
Other current liabilities | (49) | (40)
Employee benefit obligations | (88) | (113)
Other regulatory liabilities, deferred | (64) | (15)
Mississippi Power | Pension plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension costs | 78 | 0
Other regulatory assets, deferred | 146 | 235
Other current liabilities | (2) | (2)
Employee benefit obligations | (33) | (51)
Other regulatory liabilities, deferred | 0 | 0
AOCI | 0 | 0
Mississippi Power | Other postretirement benefit plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension and other postretirement benefit costs | 0 |
Other regulatory assets, deferred | 2 | 5
Other current liabilities | 0 | 0
Employee benefit obligations | (47) | (54)
Other regulatory liabilities, deferred | (1) | 0
AOCI | 0 | 0
Southern Power |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Other current liabilities | (140) | (132)
Southern Power | Pension plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension costs | 20 | 0
Other regulatory assets, deferred | 0 | 0
Other current liabilities | (2) | (2)
Employee benefit obligations | (27) | (29)
Other regulatory liabilities, deferred | 0 | 0
AOCI | 35 | 60
Southern Power | Other postretirement benefit plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension and other postretirement benefit costs | 0 |
Other regulatory assets, deferred | 0 | 0
Other current liabilities | 0 | 0
Employee benefit obligations | (11) | (12)
Other regulatory liabilities, deferred | 0 | 0
AOCI | 2 | 3
Southern Company Gas |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Other regulatory assets, deferred | 689 | 615
Other current liabilities | (155) | (150)
Employee benefit obligations | (176) | (283)
Southern Company Gas | Pension plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension costs | 175 | 70
Other regulatory assets, deferred | 91 | 205
Other current liabilities | (2) | (2)
Employee benefit obligations | (66) | (134)
Other regulatory liabilities, deferred | 0 | 0
AOCI | (45) | 1
Regulatory asset | 210 | 224
Southern Company Gas | Other postretirement benefit plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Prepaid pension and other postretirement benefit costs | 0 |
Other regulatory assets, deferred | 0 | (23)
Other current liabilities | 0 | 0
Employee benefit obligations | (94) | (120)
Other regulatory liabilities, deferred | (34) | 0
AOCI | (5) | 0
Regulatory asset | $ 40 | $ 47

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