Derivatives - Schedule of Energy-Related Derivatives (Details) - Energy-related, Natural Gas MMBTU in Millions	Mar. 31, 2022 MMBTU
Energy-related derivative contracts
Net Purchased mmBtu	279.0
ALABAMA POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	65.0
GEORGIA POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	75.0
MISSISSIPPI POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	71.0
SOUTHERN POWER CO
Energy-related derivative contracts
Net Purchased mmBtu	4.0
SOUTHERN Co GAS
Energy-related derivative contracts
Net Purchased mmBtu	64.0
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Long
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume	66.2
SOUTHERN Co GAS | Derivatives not designated as hedging instruments | Short
Energy-related derivative contracts
Derivative nonmonetary notional amount net long short position volume	2.6