DERIVATIVES - Energy-Related Derivative Contracts (Details) - Energy-related, Natural Gas MMBTU in Millions	Dec. 31, 2021 MMBTU
Derivative [Line Items]
Net Purchased mmBtu	311
Alabama Power
Derivative [Line Items]
Net Purchased mmBtu	74
Georgia Power
Derivative [Line Items]
Net Purchased mmBtu	89
Mississippi Power
Derivative [Line Items]
Net Purchased mmBtu	75
Southern Power
Derivative [Line Items]
Net Purchased mmBtu	5
Southern Company Gas
Derivative [Line Items]
Net Purchased mmBtu	68
Long | Not Designated as Hedging Instrument | Southern Company Gas
Derivative [Line Items]
Derivative nonmonetary notional amount net long short position volume	74
Short | Not Designated as Hedging Instrument | Southern Company Gas
Derivative [Line Items]
Derivative nonmonetary notional amount net long short position volume	6