Fair Value Measurements - Schedule of Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) $ in Billions |
Sep. 30, 2023
USD ($)
|
|---|---|
| Long-term debt, including securities due within one year: | |
| Carrying amount | $ 58.8 |
| Fair value | 50.8 |
| ALABAMA POWER CO | |
| Long-term debt, including securities due within one year: | |
| Carrying amount | 11.2 |
| Fair value | 9.4 |
| GEORGIA POWER CO | |
| Long-term debt, including securities due within one year: | |
| Carrying amount | 15.8 |
| Fair value | 13.4 |
| MISSISSIPPI POWER CO | |
| Long-term debt, including securities due within one year: | |
| Carrying amount | 1.6 |
| Fair value | 1.3 |
| SOUTHERN POWER CO | |
| Long-term debt, including securities due within one year: | |
| Carrying amount | 2.7 |
| Fair value | 2.4 |
| SOUTHERN Co GAS | |
| Long-term debt, including securities due within one year: | |
| Carrying amount | 8.1 |
| Fair value | $ 6.5 |