Income Taxes - Federal ITC/PTC Carryforwards (Details) - ITC and PTC carryforward $ in Millions |
Dec. 31, 2018
USD ($)
|
|---|---|
| Operating Loss Carryforwards [Line Items] | |
| Federal ITC/PTC carryforwards | $ 2,410 |
| Alabama Power | |
| Operating Loss Carryforwards [Line Items] | |
| Federal ITC/PTC carryforwards | 11 |
| Georgia Power | |
| Operating Loss Carryforwards [Line Items] | |
| Federal ITC/PTC carryforwards | 108 |
| Southern Power | |
| Operating Loss Carryforwards [Line Items] | |
| Federal ITC/PTC carryforwards | $ 2,128 |