DERIVATIVES - Location and Amount of Gain (Loss) Recognized in Income on Cash Flow and Fair Value Hedging Relationships (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative [Line Items]
Total cost of sales	$ 144	$ 191	$ 583	$ 877
Depreciation and amortization	873	755	1,730	1,506
Total interest expense, net of amounts capitalized	(444)	(429)	(900)	(859)
Total other income (expense), net	101	99	204	176
Cash Flow Hedging | Energy-related derivatives | Total cost of natural gas
Derivative [Line Items]
Gain (loss) on hedge	(1)	0	(8)	0
Cash Flow Hedging | Energy-related derivatives | Total depreciation and amortization
Derivative [Line Items]
Gain (loss) on hedge	(1)	(1)	(2)	(4)
Cash Flow Hedging | Interest rate derivatives | Total interest expense, net of amounts capitalized
Derivative [Line Items]
Gain (loss) on hedge	(6)	(5)	(13)	(9)
Cash Flow Hedging | Foreign currency derivatives | Total interest expense, net of amounts capitalized
Derivative [Line Items]
Gain (loss) on hedge	(6)	(6)	(12)	(12)
Cash Flow Hedging | Foreign currency derivatives | Total other income (expense), net
Derivative [Line Items]
Gain (loss) on hedge	27	16	(4)	(8)
Fair Value Hedging | Interest rate derivatives | Total interest expense, net of amounts capitalized
Derivative [Line Items]
Gain (loss) on hedge	1	19	30	33
SOUTHERN POWER CO
Derivative [Line Items]
Depreciation and amortization	121	119	239	237
Total interest expense, net of amounts capitalized	(38)	(41)	(77)	(84)
Total other income (expense), net	1	40	4	41
SOUTHERN POWER CO | Cash Flow Hedging | Energy-related derivatives | Total depreciation and amortization
Derivative [Line Items]
Gain (loss) on hedge	(1)	(1)	(2)	(4)
SOUTHERN POWER CO | Cash Flow Hedging | Foreign currency derivatives | Total interest expense, net of amounts capitalized
Derivative [Line Items]
Gain (loss) on hedge	(6)	(6)	(12)	(12)
SOUTHERN POWER CO | Cash Flow Hedging | Foreign currency derivatives | Total other income (expense), net
Derivative [Line Items]
Gain (loss) on hedge	$ 27	$ 16	$ (4)	$ (8)