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Fair Value Measurements (Tables) | 6 Months Ended
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Jun. 30, 2023
Fair Value Disclosures [Abstract] |
Schedule of Assets and Liabilities Measured at Fair Value | At June 30, 2023, assets and liabilities measured at fair value on a recurring basis during the period, together with their associated level of the fair value hierarchy, were as follows:
| Fair Value Measurements Using: |  |
At June 30, 2023 | Quoted Prices in Active Markets for Identical Assets (Level 1) |  | Significant Other Observable Inputs (Level 2) |  | Significant Unobservable Inputs (Level 3) |  | Net Asset Value as a Practical Expedient (NAV) |  | Total
| (in millions)
Southern Company |  |  |  |  |  |  |  |  |
Assets: |  |  |  |  |  |  |  |  |
Energy-related derivatives(a) | $ | 7 |  |  | $ | 86 |  |  | $ | — |  |  | $ | — |  |  | $ | 93 |
Interest rate derivatives | — |  |  | 4 |  |  | — |  |  | — |  |  | 4 |
Investments in trusts:(b)(c) |  |  |  |  |  |  |  |  |
Domestic equity | 718 |  |  | 205 |  |  | — |  |  | — |  |  | 923 |
Foreign equity | 140 |  |  | 167 |  |  | — |  |  | — |  |  | 307 |
U.S. Treasury and government agency securities | — |  |  | 333 |  |  | — |  |  | — |  |  | 333 |
Municipal bonds | — |  |  | 46 |  |  | — |  |  | — |  |  | 46 |
Pooled funds – fixed income | — |  |  | 7 |  |  | — |  |  | — |  |  | 7 |
Corporate bonds | — |  |  | 391 |  |  | — |  |  | — |  |  | 391 |
Mortgage and asset backed securities | — |  |  | 90 |  |  | — |  |  | — |  |  | 90 |
Private equity | — |  |  | — |  |  | — |  |  | 166 |  |  | 166 |
Cash and cash equivalents | 2 |  |  | — |  |  | — |  |  | — |  |  | 2 |
Other | 31 |  |  | 7 |  |  | — |  |  | 9 |  |  | 47 |
Cash equivalents | 1,494 |  |  | 12 |  |  | — |  |  | — |  |  | 1,506 |
Other investments | 9 |  |  | 34 |  |  | 8 |  |  | — |  |  | 51 |
Total | $ | 2,401 |  |  | $ | 1,382 |  |  | $ | 8 |  |  | $ | 175 |  |  | $ | 3,966 |
Liabilities: |  |  |  |  |  |  |  |  |
Energy-related derivatives(a) | $ | 33 |  |  | $ | 278 |  |  | $ | — |  |  | $ | — |  |  | $ | 311 |
Interest rate derivatives | — |  |  | 304 |  |  | — |  |  | — |  |  | 304 |
Foreign currency derivatives | — |  |  | 170 |  |  | — |  |  | — |  |  | 170 |
Contingent consideration | — |  |  | — |  |  | 12 |  |  | — |  |  | 12 |
Other | — |  |  | 13 |  |  | — |  |  | — |  |  | 13 |
Total | $ | 33 |  |  | $ | 765 |  |  | $ | 12 |  |  | $ | — |  |  | $ | 810 |
| Fair Value Measurements Using: |  |
At June 30, 2023 | Quoted Prices in Active Markets for Identical Assets (Level 1) |  | Significant Other Observable Inputs (Level 2) |  | Significant Unobservable Inputs (Level 3) |  | Net Asset Value as a Practical Expedient (NAV) |  | Total
| (in millions)
Alabama Power |  |  |  |  |  |  |  |  |
Assets: |  |  |  |  |  |  |  |  |
Energy-related derivatives | $ | — |  |  | $ | 32 |  |  | $ | — |  |  | $ | — |  |  | $ | 32 |
Nuclear decommissioning trusts:(b) |  |  |  |  |  |  |  |  |
Domestic equity | 420 |  |  | 198 |  |  | — |  |  | — |  |  | 618 |
Foreign equity | 140 |  |  | — |  |  | — |  |  | — |  |  | 140 |
U.S. Treasury and government agency securities | — |  |  | 20 |  |  | — |  |  | — |  |  | 20 |
Municipal bonds | — |  |  | 1 |  |  | — |  |  | — |  |  | 1 |
Corporate bonds | — |  |  | 221 |  |  | — |  |  | — |  |  | 221 |
Mortgage and asset backed securities | — |  |  | 21 |  |  | — |  |  | — |  |  | 21 |
Private equity | — |  |  | — |  |  | — |  |  | 166 |  |  | 166 |
Other | 7 |  |  | — |  |  | — |  |  | 9 |  |  | 16 |
Cash equivalents | 110 |  |  | 12 |  |  | — |  |  | — |  |  | 122 |
Other investments | — |  |  | 34 |  |  | — |  |  | — |  |  | 34 |
Total | $ | 677 |  |  | $ | 539 |  |  | $ | — |  |  | $ | 175 |  |  | $ | 1,391 |
Liabilities: |  |  |  |  |  |  |  |  |
Energy-related derivatives | $ | — |  |  | $ | 84 |  |  | $ | — |  |  | $ | — |  |  | $ | 84 |
Georgia Power |  |  |  |  |  |  |  |  |
Assets: |  |  |  |  |  |  |  |  |
Energy-related derivatives | $ | — |  |  | $ | 17 |  |  | $ | — |  |  | $ | — |  |  | $ | 17 |
Nuclear decommissioning trusts:(b)(c) |  |  |  |  |  |  |  |  |
Domestic equity | 298 |  |  | 1 |  |  | — |  |  | — |  |  | 299 |
Foreign equity |  |  | 166 |  |  | — |  |  | — |  |  | 166 |
U.S. Treasury and government agency securities | — |  |  | 313 |  |  | — |  |  | — |  |  | 313 |
Municipal bonds | — |  |  | 45 |  |  | — |  |  | — |  |  | 45 |
Corporate bonds | — |  |  | 170 |  |  | — |  |  | — |  |  | 170 |
Mortgage and asset backed securities | — |  |  | 69 |  |  | — |  |  | — |  |  | 69 |
Other | 24 |  |  | 7 |  |  | — |  |  | — |  |  | 31 |
Total | $ | 322 |  |  | $ | 788 |  |  | $ | — |  |  | $ | — |  |  | $ | 1,110 |
Liabilities: |  |  |  |  |  |  |  |  |
Energy-related derivatives | $ | — |  |  | $ | 102 |  |  | $ | — |  |  | $ | — |  |  | $ | 102 |
| Fair Value Measurements Using: |  |
At June 30, 2023 | Quoted Prices in Active Markets for Identical Assets (Level 1) |  | Significant Other Observable Inputs (Level 2) |  | Significant Unobservable Inputs (Level 3) |  | Net Asset Value as a Practical Expedient (NAV) |  | Total
| (in millions)
Mississippi Power |  |  |  |  |  |  |  |  |
Assets: |  |  |  |  |  |  |  |  |
Energy-related derivatives | $ | — |  |  | $ | 27 |  |  | $ | — |  |  | $ | — |  |  | $ | 27 |
Liabilities: |  |  |  |  |  |  |  |  |
Energy-related derivatives | $ | — |  |  | $ | 55 |  |  | $ | — |  |  | $ | — |  |  | $ | 55 |
Southern Power |  |  |  |  |  |  |  |  |
Assets: |  |  |  |  |  |  |  |  |
Energy-related derivatives | $ | — |  |  | $ | 4 |  |  | $ | — |  |  | $ | — |  |  | $ | 4 |
Cash equivalents | 5 |  |  | — |  |  | — |  |  | — |  |  | 5 |
Total | $ | 5 |  |  | $ | 4 |  |  | $ | — |  |  | $ | — |  |  | $ | 9 |
Liabilities: |  |  |  |  |  |  |  |  |
Energy-related derivatives | $ | — |  |  | $ | 10 |  |  | $ | — |  |  | $ | — |  |  | $ | 10 |
Foreign currency derivatives | — |  |  | 28 |  |  | — |  |  | — |  |  | 28 |
Contingent consideration | — |  |  | — |  |  | 12 |  |  | — |  |  | 12 |
Other | — |  |  | 13 |  |  | — |  |  | — |  |  | 13 |
Total | $ | — |  |  | $ | 51 |  |  | $ | 12 |  |  | $ | — |  |  | $ | 63 |
Southern Company Gas |  |  |  |  |  |  |  |  |
Assets: |  |  |  |  |  |  |  |  |
Energy-related derivatives(a) | $ | 7 |  |  | $ | 6 |  |  | $ | — |  |  | $ | — |  |  | $ | 13 |
Interest rate derivatives | — |  |  | 4 |  |  | — |  |  | — |  |  | 4 |
Non-qualified deferred compensation trusts: |  |  |  |  |  |  |  |  |
Domestic equity | — |  |  | 6 |  |  | — |  |  | — |  |  | 6 |
Foreign equity | — |  |  | 1 |  |  | — |  |  | — |  |  | 1 |
Pooled funds – fixed income | — |  |  | 7 |  |  | — |  |  | — |  |  | 7 |
Cash equivalents | 2 |  |  | — |  |  | — |  |  | — |  |  | 2 |
Cash equivalents and restricted cash | 215 |  |  | — |  |  | — |  |  | — |  |  | 215 |
Total | $ | 224 |  |  | $ | 24 |  |  | $ | — |  |  | $ | — |  |  | $ | 248 |
Liabilities: |  |  |  |  |  |  |  |  |
Energy-related derivatives(a) | $ | 33 |  |  | $ | 27 |  |  | $ | — |  |  | $ | — |  |  | $ | 60 |
Interest rate derivatives | — |  |  | 88 |  |  | — |  |  | — |  |  | 88 |
Total | $ | 33 |  |  | $ | 115 |  |  | $ | — |  |  | $ | — |  |  | $ | 148 |
(a)Excludes cash collateral of $52 million. (b)Excludes receivables related to investment income, pending investment sales, payables related to pending investment purchases, and currencies. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information. (c)Includes investment securities pledged to creditors and collateral received and excludes payables related to the securities lending program. At June 30, 2023, approximately $25 million of the fair market value of Georgia Power's nuclear decommissioning trust funds' securities were on loan to creditors under the funds' managers' securities lending program. See Note 6 to the financial statements in Item 8 of the Form 10-K for additional information.
Schedule of Increase (Decrease) In Fair Value Of Funds | The fair value of the funds, including reinvested interest and dividends and excluding the funds' expenses, increased (decreased) by the amounts shown in the table below for the three and six months ended June 30, 2023 and 2022. The changes were recorded as a change to the regulatory assets and liabilities related to AROs for Georgia Power and Alabama Power, respectively.
| Three Months Ended | Six Months Ended
Fair value increases (decreases) | June 30, 2023 | June 30, 2022 | June 30, 2023 | June 30, 2022
| (in millions)
Southern Company | $ | 132 |  | $ | (230) |  | $ | 228 |  | $ | (380) |
Alabama Power | 58 |  | (125) |  | 103 |  | (192) |
Georgia Power | 74 |  | (105) |  | 125 |  | (188) |
Schedule of Financial Instruments for which Carrying Amount Did Not Equal Fair Value | At June 30, 2023, other financial instruments for which the carrying amount did not equal fair value were as follows:
| Southern Company | Alabama Power | Georgia Power | Mississippi Power | Southern Power | Southern Company Gas(*)
| (in billions)
Long-term debt, including securities due within one year: |  |  |  |
Carrying amount | $ | 58.9 |  | $ | 10.8 |  | $ | 16.5 |  | $ | 1.6 |  | $ | 3.0 |  | $ | 7.5 |
Fair value | 53.5 |  | 9.5 |  | 15.0 |  | 1.4 |  | 2.8 |  | 6.6 |
(*)The long-term debt of Southern Company Gas is recorded at amortized cost, including the fair value adjustments at the effective date of the 2016 merger with Southern Company. Southern Company Gas amortizes the fair value adjustments over the remaining lives of the respective bonds, the latest being through 2043.

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- Definition Tabular disclosure of assets and liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482106/820-10-50-2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482106/820-10-50-2 + Details
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