Derivatives - Schedule of Pre-Tax Effects of Cash Flow and Fair Value Hedging on Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative [Line Items]
Depreciation and amortization	$ 896	$ 889	$ 2,658	$ 2,619
Total interest expense, net of amounts capitalized	(451)	(443)	(1,352)	(1,343)
Total other income (expense), net	131	113	297	319
Natural gas
Derivative [Line Items]
Total cost of sales	129	71	943	654
Other Income (Expense)
Derivative [Line Items]
Amount excluded from effectiveness testing recognized in earnings	4	0	4	0
Cash Flow Hedging | Energy-related derivatives | Cost of Sales
Derivative [Line Items]
Gain (loss) on hedges	2	0	0	(8)
Cash Flow Hedging | Energy-related derivatives | Depreciation and Amortization
Derivative [Line Items]
Gain (loss) on hedges	3	(1)	6	(3)
Cash Flow Hedging | Interest rate derivatives | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(7)	(6)	(20)	(19)
Cash Flow Hedging | Foreign currency derivatives | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(6)	(6)	(18)	(18)
Cash Flow Hedging | Foreign currency derivatives | Other Income (Expense)
Derivative [Line Items]
Gain (loss) on hedges	(34)	56	(76)	52
Fair Value Hedging | Interest rate derivatives | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(4)	(3)	(16)	27
Fair Value Hedging | Foreign currency derivatives | Other Income (Expense)
Derivative [Line Items]
Gain (loss) on hedges	(32)	0	(32)	0
SOUTHERN POWER CO
Derivative [Line Items]
Depreciation and amortization	132	129	383	367
Total interest expense, net of amounts capitalized	(36)	(36)	(111)	(114)
Total other income (expense), net	2	13	10	19
SOUTHERN POWER CO | Cash Flow Hedging | Energy-related derivatives | Depreciation and Amortization
Derivative [Line Items]
Gain (loss) on hedges	3	(1)	6	(3)
SOUTHERN POWER CO | Cash Flow Hedging | Foreign currency derivatives | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(6)	(6)	(18)	(18)
SOUTHERN POWER CO | Cash Flow Hedging | Foreign currency derivatives | Other Income (Expense)
Derivative [Line Items]
Gain (loss) on hedges	$ (34)	$ 56	$ (76)	$ 52