DERIVATIVES - Energy-Related Derivative Contracts (Details) - Energy-related, Natural Gas MMBTU in Millions	Dec. 31, 2019 MMBTU
Derivative [Line Items]
Net Purchased mmBtu	589
Alabama Power
Derivative [Line Items]
Net Purchased mmBtu	88
Georgia Power
Derivative [Line Items]
Net Purchased mmBtu	175
Mississippi Power
Derivative [Line Items]
Net Purchased mmBtu	101
Southern Power
Derivative [Line Items]
Net Purchased mmBtu	7
Southern Company Gas
Derivative [Line Items]
Net Purchased mmBtu	218
Long | Not Designated as Hedging Instrument | Southern Company Gas
Derivative [Line Items]
Derivative nonmonetary notional amount net long short position volume	4,096
Short | Not Designated as Hedging Instrument | Southern Company Gas
Derivative [Line Items]
Derivative nonmonetary notional amount net long short position volume	3,878