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REGULATORY MATTERS - APC Rate NDR and Reliability Reserve Accounting Order (Details) - USD ($) | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Dec. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Sep. 30, 2022 | Jul. 12, 2022
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Reliability reserve, amount deferred | $ 63,000,000 | $ 63,000,000 | $ 191,000,000 |  |  |
Net regulatory assets | 6,523,000,000 | 6,523,000,000 | 5,833,000,000 |  |  |
Plant in service, net of depreciation | 90,703,000,000 | 90,703,000,000 | 82,232,000,000 |  |  |
Other utility plant, net | 499,000,000 | 499,000,000 | 599,000,000 |  |  |
Other regulatory assets | 1,120,000,000 | 1,120,000,000 | 860,000,000 |  |  |
Reliability reserves |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Net regulatory assets | (179,000,000) | (179,000,000) | (191,000,000) |  |  |
Revision of Prior Period, Reclassification, Adjustment |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Plant in service, net of depreciation |  |  | (42,000,000) |  | $ (600,000,000) |
Other utility plant, net |  |  |  |  | $ 600,000,000 |
Other regulatory assets |  |  | 42,000,000 |  |  |
Alabama Power |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Minimum natural disaster reserve balance, triggering establishment charge | 50,000,000 | 50,000,000 |  |  |  |
Natural disaster reserve authorized limit | 75,000,000 | 75,000,000 |  |  |  | $ 35,000,000
Reliability reserve, amount deferred | 52,000,000 | 52,000,000 | 166,000,000 |  |  |
Net regulatory assets | 2,720,000,000 | 2,720,000,000 | 2,340,000,000 |  |  |
Maximum rate NDR charge per month, monthly nonresidential customer account | 5 | 5 |  |  |  | 10.00
Maximum rate NDR charge per month, monthly residential customer account | 2.50 | 2.50 |  |  |  | $ 5.00
Additional accruals authorized by state PSCs |  |  |  | $ 65,000,000 |  |
Annual recovery amount |  | 12,000,000 | 14,000,000 | $ 6,000,000 |  |
Regulatory asset, amortization period | 76,000,000 | 76,000,000 | 97,000,000 |  |  |
NDR, expected recovery amount |  | 12,000,000 |  |  |  |
Plant in service, net of depreciation | 24,298,000,000 | 24,298,000,000 | 23,002,000,000 |  |  |
Other utility plant, net | 499,000,000 | 499,000,000 | 599,000,000 |  |  |
Other regulatory assets | 385,000,000 | 385,000,000 | 372,000,000 |  |  |
Alabama Power | Reliability reserves |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Net regulatory assets | (143,000,000) | $ (143,000,000) | $ (166,000,000) |  |  |
Accrual | $ 75,000,000 |  |  |  |  |
Alabama Power | Minimum |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Maximum period for recovery deferred stock related operations and maintenance costs and any future reserve deficits |  | 24 months |  |  |  |
Alabama Power | Maximum |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Maximum period for recovery deferred stock related operations and maintenance costs and any future reserve deficits |  | 48 months |  |  |  |

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