Derivatives - Interest Rate Derivatives (Details) - Interest rate derivatives $ in Millions |
12 Months Ended |
|---|---|
|
Dec. 31, 2018
USD ($)
| |
| Derivative [Line Items] | |
| Notional Amount | $ 2,000 |
| Fair value gain (loss) at December 31, 2018 | (49) |
| Southern Company | Maturity Date June 2020 | Fair Value Hedges of Existing Debt | |
| Derivative [Line Items] | |
| Notional Amount | $ 300 |
| Interest Rate Received | 2.75% |
| Weighted Average Interest Rate Paid | 0.92% |
| Fair value gain (loss) at December 31, 2018 | $ (4) |
| Southern Company | Maturity Date June 2021 | Fair Value Hedges of Existing Debt | |
| Derivative [Line Items] | |
| Notional Amount | $ 1,500 |
| Interest Rate Received | 2.35% |
| Weighted Average Interest Rate Paid | 0.87% |
| Fair value gain (loss) at December 31, 2018 | $ (43) |
| Georgia Power | Maturity Date December 2019 | Fair Value Hedges of Existing Debt | |
| Derivative [Line Items] | |
| Notional Amount | $ 200 |
| Interest Rate Received | 4.25% |
| Weighted Average Interest Rate Paid | 2.46% |
| Fair value gain (loss) at December 31, 2018 | $ (2) |