Property, Plant, and Equipment - Additional Information (Narrative) (Details) |
12 Months Ended |
|---|---|
Dec. 31, 2018 | |
| Alabama Power | |
| Property, Plant and Equipment [Line Items] | |
| Period to amortize costs | 18 months |
| Plant Vogtle Units 1 and 2 | Georgia Power | |
| Property, Plant and Equipment [Line Items] | |
| Unit operating cycle (term) | 18 months |
| Plant Hatch Units 1 and 2 | Georgia Power | |
| Property, Plant and Equipment [Line Items] | |
| Unit operating cycle (term) | 24 months |