Property, Plant, and Equipment - Composite Straight-Line Rates (Details) - Utility plant in service |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Alabama Power | |||
| Property, Plant and Equipment [Line Items] | |||
| Composite rate | 3.00% | 2.90% | 3.00% |
| Georgia Power | |||
| Property, Plant and Equipment [Line Items] | |||
| Composite rate | 2.60% | 2.70% | 2.80% |
| Mississippi Power | |||
| Property, Plant and Equipment [Line Items] | |||
| Composite rate | 4.10% | 3.70% | 4.20% |
| Southern Company Gas | |||
| Property, Plant and Equipment [Line Items] | |||
| Composite rate | 2.90% | 2.90% | 2.80% |