FINANCING - Bank Credit Arrangements Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Line of Credit Facility [Line Items]
Ratio of indebtedness to capitalization, debt covenant, required	70.00%
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	$ 1,500
Other Subsidiaries
Line of Credit Facility [Line Items]
Ratio of indebtedness to capitalization, debt covenant, required	65.00%
Alabama Power
Line of Credit Facility [Line Items]
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	$ 789
Georgia Power
Line of Credit Facility [Line Items]
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	672
Remarketed pollution control bonds	157
Mississippi Power
Line of Credit Facility [Line Items]
Amount of variable rate pollution control revenue bonds outstanding requiring liquidity support	34
Southern Power | Power Purchase Agreement
Line of Credit Facility [Line Items]
Debt instrument, collateral amount	$ 105	$ 105