DERIVATIVES - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Long-term debt - Fair Value Hedging - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Amount of the Hedged Item	$ (2,927)	$ (3,280)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	282	9
Southern Company Gas
Derivative Instruments, Gain (Loss) [Line Items]
Carrying Amount of the Hedged Item	(415)	(493)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	$ 81	$ 2