DERIVATIVES - Pre-Tax Effects of Derivatives Designated as Hedges on Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Derivative Instruments, Gain (Loss) [Line Items]
Total other operations and maintenance	$ 6,093	$ 6,573	$ 5,902
Depreciation and amortization	4,525	3,663	3,565
Interest expense, net of amounts capitalized	(2,446)	(2,022)	(1,837)
Other income (expense), net	553	500	449
Natural gas
Derivative Instruments, Gain (Loss) [Line Items]
Cost of sales	1,644	3,004	1,619
Energy-related derivatives | Cost of Sales | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	(44)	37	17
Energy-related derivatives | Operating Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on hedges	(2)	0	0
Energy-related derivatives | Depreciation and Amortization | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	(23)	(5)	9
Interest rate derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	(35)	(25)	(27)
Interest rate derivatives | Interest Expense | Fair Value Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	37	(291)	(30)
Foreign currency derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	(11)	(19)	(24)
Foreign currency derivatives | Other Income (Expense) | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	19	(83)	(104)
Gain (loss) on foreign currency fair value hedges	69	(106)	(63)
Amount excluded from effectiveness testing recognized in earnings	(21)	24	3
Southern Power
Derivative Instruments, Gain (Loss) [Line Items]
Total other operations and maintenance	473	482	423
Depreciation and amortization	504	516	517
Interest expense, net of amounts capitalized	(129)	(138)	(147)
Other income (expense), net	12	7	10
Southern Power | Energy-related derivatives | Depreciation and Amortization | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	(23)	(5)	9
Southern Power | Foreign currency derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	(11)	(19)	(24)
Southern Power | Foreign currency derivatives | Other Income (Expense) | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	19	(83)	(104)
Southern Company Gas
Derivative Instruments, Gain (Loss) [Line Items]
Cost of sales	1,644	3,004	1,619
Total other operations and maintenance	1,194	1,176	1,072
Depreciation and amortization	582	559	536
Interest expense, net of amounts capitalized	(310)	(263)	(238)
Other income (expense), net	57	53	(53)
Southern Company Gas | Energy-related derivatives | Operating Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on hedges	(2)	0	0
Southern Company Gas | Interest rate derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on hedges	(19)	(4)	0
Southern Company Gas | Interest rate derivatives | Interest Expense | Fair Value Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on hedges	6	(86)	0
Southern Company Gas | Foreign currency derivatives | Other Income (Expense) | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	$ (44)	$ 37	$ 17