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Financing - Schedule of Credit Arrangements (Details) - USD ($) $ in Millions | Sep. 30, 2025 | Mar. 31, 2025 | Feb. 28, 2025
--- | --- | --- | ---
Line of Credit Facility [Line Items] |  |  |
2026 | $ 45 |  |
2027 | 625 |  |
2029 | 650 |  |
2030 | 7,600 |  |
Total | 8,920 |  |
Unused | 8,909 |  |
Expires within One Year | 30 |  |
Southern Company parent |  |  |
Line of Credit Facility [Line Items] |  |  |
2026 | 0 |  |
2027 | 500 |  |
2029 | 0 |  |
2030 | 2,500 |  |
Total | 3,000 |  |
Unused | 2,999 |  |
Expires within One Year | 0 |  |
2028 |  |  | $ 150
ALABAMA POWER CO |  |  |
Line of Credit Facility [Line Items] |  |  |
2026 | 15 |  |
2027 | 0 |  |
2029 | 650 |  |
2030 | 700 |  |
Total | 1,365 |  |
Unused | 1,365 |  |
Expires within One Year | 0 |  |
GEORGIA POWER CO |  |  |
Line of Credit Facility [Line Items] |  |  |
2026 | 0 |  |
2027 | 0 |  |
2029 | 0 |  |
2030 | 2,050 |  | 1,750
Total | 2,050 |  |
Unused | 2,042 |  |
Expires within One Year | 0 |  |
GEORGIA POWER CO | Uncommited Letter Of Credit Facility |  |  |
Line of Credit Facility [Line Items] |  |  |
Letters of credit outstanding | 26 |  |
MISSISSIPPI POWER CO |  |  |
Line of Credit Facility [Line Items] |  |  |
2026 | 0 |  |
2027 | 125 |  |
2029 | 0 |  |
2030 | 150 |  |
Total | 275 |  |
Unused | 275 |  |
Expires within One Year | 0 |  |
SOUTHERN POWER CO |  |  |
Line of Credit Facility [Line Items] |  |  |
2026 | 0 |  |
2027 | 0 |  |
2029 | 0 |  |
2030 | 600 |  |
Total | 600 |  |
Unused | 600 |  |
Expires within One Year | 0 |  |
SOUTHERN POWER CO | Continuing Letter of Credit Facility A |  |  |
Line of Credit Facility [Line Items] |  |  |
Total | 75 |  |
Unused | 17 |  |
SOUTHERN POWER CO | Continuing Letter of Credit Facility B |  |  |
Line of Credit Facility [Line Items] |  |  |
Total | 100 |  |
Unused | 4 |  |
SOUTHERN POWER CO | Uncommited Letter Of Credit Facility |  |  |
Line of Credit Facility [Line Items] |  |  |
Letters of credit outstanding | 23 |  |
SOUTHERN Co GAS |  |  |
Line of Credit Facility [Line Items] |  |  |
2026 | 0 |  |
2027 | 0 |  |
2029 | 0 |  | 1,500
2030 | 1,600 |  |
Total | 1,600 |  |
Unused | 1,598 |  |
Expires within One Year | 0 |  |
SEGCO |  |  |
Line of Credit Facility [Line Items] |  |  |
2026 | 30 |  |
2027 | 0 |  |
2029 | 0 |  |
2030 | 0 |  |
Total | 30 |  |
Unused | 30 |  |
Expires within One Year | 30 |  |
Southern Company, Southern Power, And Mississippi Power |  |  |
Line of Credit Facility [Line Items] |  |  |
2030 | 3,250 |  |
Total |  | $ 3,250 | $ 2,450
Alabama Property Company |  |  |
Line of Credit Facility [Line Items] |  |  |
2026 | 15 |  |
Unused | 15 |  |
Southern Company Gas Capital |  |  |
Line of Credit Facility [Line Items] |  |  |
2030 | 800 | 800 |
Nicor Gas |  |  |
Line of Credit Facility [Line Items] |  |  |
2030 | $ 800 | $ 800 |

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