DERIVATIVES - Pre-Tax Effects of Derivatives Not Designated as Hedging (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Energy-related derivatives | Natural gas revenues
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ 0	$ (11,000,000)	$ (117,000,000)
Energy-related derivatives | Cost of natural gas
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	59,000,000	(65,000,000)	(27,000,000)
Energy-related derivatives | Cost of natural gas | Not Designated as Hedging Instrument | Southern Company Gas
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	59,000,000	(76,000,000)	(144,000,000)
Weather derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ 15,000,000	$ (7,000,000)	$ 0