Fair Value Measurements - Schedule of Increase (Decrease) In Fair Value Of Funds (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2023 |
Sep. 30, 2022 |
Sep. 30, 2023 |
Sep. 30, 2022 |
|
| Fair Value, Option, Quantitative Disclosures [Line Items] | ||||
| Increase (decrease) in fair value of funds | $ (4) | $ (106) | $ 211 | $ (486) |
| ALABAMA POWER CO | ||||
| Fair Value, Option, Quantitative Disclosures [Line Items] | ||||
| Increase (decrease) in fair value of funds | (36) | (53) | 54 | (245) |
| GEORGIA POWER CO | ||||
| Fair Value, Option, Quantitative Disclosures [Line Items] | ||||
| Increase (decrease) in fair value of funds | $ 32 | $ (53) | $ 157 | $ (241) |