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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Amortization of Other Intangible Assets (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Finite-Lived Intangible Assets [Line Items] |  |  |
Amortization associated with other intangible assets | $ 38 | $ 39 | $ 44
Estimated future amortization |  |  |
2024 | 35 |  |
2025 | 32 |  |
2026 | 27 |  |
2027 | 24 |  |
2028 | 24 |  |
Southern Power |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Amortization associated with other intangible assets | 20 | 20 | 20
Estimated future amortization |  |  |
2024 | 20 |  |
2025 | 20 |  |
2026 | 20 |  |
2027 | 20 |  |
2028 | 20 |  |
Southern Company Gas |  |  |
Estimated future amortization |  |  |
2024 | 7 |  |
2025 | 6 |  |
2026 | 3 |  |
2027 | 0 |  |
2028 | 0 |  |
Southern Company Gas | Gas marketing services |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Amortization associated with other intangible assets | 10 | $ 11 | $ 15
Operating Revenues |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Amortization associated with other intangible assets | $ 20 |  |

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- Definition The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (b) -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482740/230-10-45-28 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482686/350-30-45-2 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482665/350-30-50-2 + Details
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