Derivatives - Pre-tax Effects of Derivatives as Fair Value Hedging Relationships (Details) - Interest Rate Contract [Member] - Interest Expense [Member] - Fair Value Hedging [Member] - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2017 |
Mar. 31, 2016 |
|
| Southern Company [Member] | ||
| Derivative Instruments, Gain (Loss) [Line Items] | ||
| Derivative assets, fair value, gross asset | $ (8) | $ 20 |
| Georgia Power [Member] | ||
| Derivative Instruments, Gain (Loss) [Line Items] | ||
| Derivative assets, fair value, gross asset | $ (1) | $ 14 |