Derivatives - Foreign Currency Derivatives (Details) - 6 months ended Jun. 30, 2019 - Cash Flow Hedges of Forecasted Debt - Foreign currency derivatives € in Millions, $ in Millions |
USD ($) |
EUR (€) |
|---|---|---|
| Derivative [Line Items] | ||
| Pay Notional | $ 1,241 | |
| Receive Notional | € | € 1,100 | |
| Fair Value Gain (Loss) at June 30, 2019 | 37 | |
| SOUTHERN POWER CO | June 2022 | ||
| Derivative [Line Items] | ||
| Pay Notional | $ 677 | |
| Pay Rate | 2.95% | |
| Receive Notional | € | 600 | |
| Receive Rate | 1.00% | |
| Fair Value Gain (Loss) at June 30, 2019 | $ 14 | |
| SOUTHERN POWER CO | June 2026 | ||
| Derivative [Line Items] | ||
| Pay Notional | $ 564 | |
| Pay Rate | 3.78% | |
| Receive Notional | € | € 500 | |
| Receive Rate | 1.85% | |
| Fair Value Gain (Loss) at June 30, 2019 | $ 23 |