DERIVATIVES - Pre-Tax Effects of Derivatives Designated as Hedges on Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Depreciation and amortization	$ 3,565	$ 3,518	$ 3,038
Interest expense, net of amounts capitalized	(1,837)	(1,821)	(1,736)
Other income (expense), net	456	336	252
Energy-related derivatives | Cost of Sales | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	17	(8)	(2)
Energy-related derivatives | Depreciation and Amortization | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	9	(3)	(6)
Interest rate derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	(27)	(26)	(20)
Interest rate derivatives | Interest Expense | Fair Value Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	(30)	27	42
Foreign currency derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	(24)	(23)	(24)
Foreign currency derivatives | Other Income (Expense) | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	(104)	114	(24)
Gain (loss) on foreign currency fair value hedges	(63)	0	0
Amount excluded from effectiveness testing recognized in earnings	3	0	0
Southern Power
Derivative Instruments, Gain (Loss) [Line Items]
Depreciation and amortization	517	494	479
Interest expense, net of amounts capitalized	(147)	(151)	(169)
Other income (expense), net	10	19	47
Southern Power | Energy-related derivatives | Depreciation and Amortization | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	9	(3)	(6)
Southern Power | Foreign currency derivatives | Interest Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	(24)	(23)	(24)
Southern Power | Foreign currency derivatives | Other Income (Expense) | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	(104)	114	(24)
Southern Company Gas
Derivative Instruments, Gain (Loss) [Line Items]
Depreciation and amortization	536	500	487
Interest expense, net of amounts capitalized	(238)	(231)	(232)
Other income (expense), net	(53)	41	20
Southern Company Gas | Foreign currency derivatives | Other Income (Expense) | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative	$ 17	$ (8)	$ (2)