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DERIVATIVES - Narrative (Details) MMBTU in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2021 USD ($) MMBTU | Dec. 31, 2020 USD ($)
Derivative [Line Items] |  |
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | 26 |
Estimated pre-tax gains (losses) that will be reclassified from OCI to interest expense for the next 12-month period | $ | $ (21,000,000) |
Collateral already posted, aggregate fair value | $ |  | $ 28,000,000
Alabama Power |  |
Derivative [Line Items] |  |
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | 6 |
Georgia Power |  |
Derivative [Line Items] |  |
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | 8 |
Mississippi Power |  |
Derivative [Line Items] |  |
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | 4 |
Southern Power |  |
Derivative [Line Items] |  |
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | 8 |
Parent Company and Southern Power |  |
Derivative [Line Items] |  |
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months | $ | $ (13,000,000) |
Registrants | Derivative Counterparties |  |
Derivative [Line Items] |  |
Collateral already posted, aggregate fair value | $ | $ 0 |

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- Definition The estimated net amount of unrealized gains or losses on foreign currency cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121549185&loc=d3e80748-113994 + Details
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