DERIVATIVES - Energy-Related Derivatives (Details) - Energy-related, Natural Gas MMBTU in Millions	Jun. 30, 2020 MMBTU
Energy-related derivative contracts
Net Purchased mmBtu	944
ALABAMA POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	85
GEORGIA POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	152
MISSISSIPPI POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	91
SOUTHERN POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	15
SOUTHERN Co GAS
Energy-related derivative contracts
Net Purchased mmBtu	601
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Long
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume	4,600
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Short
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume	4,000