FAIR VALUE MEASUREMENTS - Schedule of Increase (Decrease) In Fair Value Of Funds (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2020 |
Jun. 30, 2019 |
Jun. 30, 2020 |
Jun. 30, 2019 |
|
| Fair Value, Option, Quantitative Disclosures [Line Items] | ||||
| Increase (decrease) in fair value of funds | $ 223 | $ 75 | $ (23) | $ 227 |
| ALABAMA POWER CO | ||||
| Fair Value, Option, Quantitative Disclosures [Line Items] | ||||
| Increase (decrease) in fair value of funds | 124 | 38 | (42) | 125 |
| GEORGIA POWER CO | ||||
| Fair Value, Option, Quantitative Disclosures [Line Items] | ||||
| Increase (decrease) in fair value of funds | $ 99 | $ 37 | $ 19 | $ 102 |