Derivatives - Schedule of Energy-Related Derivatives (Details) - Energy-related, Natural Gas MMBTU in Millions	Jun. 30, 2021 MMBTU
Energy-related derivative contracts
Net Purchased mmBtu	978
ALABAMA POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	73
GEORGIA POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	125
MISSISSIPPI POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	85
SOUTHERN POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	9
SOUTHERN Co GAS
Energy-related derivative contracts
Net Purchased mmBtu	686
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	3,900