DERIVATIVES - Interest Rate Derivatives (Details) - Interest rate derivatives $ in Millions |
6 Months Ended |
|---|---|
|
Jun. 30, 2020
USD ($)
| |
| Derivative [Line Items] | |
| Notional Amount | $ 1,760 |
| Fair Value Gain (Loss) at June 30, 2020 | 0 |
| SOUTHERN Co GAS | Cash Flow Hedges of Forecasted Debt | |
| Derivative [Line Items] | |
| Notional Amount | $ 200 |
| Weighted Average Interest Rate Paid | 1.81% |
| Fair Value Gain (Loss) at June 30, 2020 | $ (23) |
| MISSISSIPPI POWER CO | Cash Flow Hedges of Existing Debt | |
| Derivative [Line Items] | |
| Notional Amount | $ 60 |
| Weighted Average Interest Rate Paid | 0.58% |
| Fair Value Gain (Loss) at June 30, 2020 | $ 0 |
| Southern Company | Fair Value Hedges of Existing Debt | |
| Derivative [Line Items] | |
| Notional Amount | $ 1,500 |
| Interest Rate Received | 2.35% |
| Fair Value Gain (Loss) at June 30, 2020 | $ 23 |
| London Interbank Offered Rate (LIBOR) | Southern Company | Fair Value Hedges of Existing Debt | |
| Derivative [Line Items] | |
| Weighted Average Interest Rate Paid | 0.87% |