Derivatives - Schedule of Pre-Tax Effects of Cash Flow and Fair Value Hedging on Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Other Income (Expense)
Derivative [Line Items]
Amount excluded from effectiveness testing recognized in earnings	$ (3)	$ 5	$ 13	$ 5
Cash Flow Hedging | Energy-related derivatives | Cost of Goods and Services Sold | Fuel
Derivative [Line Items]
Gain (loss) on hedges	0	(1)	1	(2)
Cash Flow Hedging | Energy-related derivatives | Cost of Goods and Services Sold | Natural gas
Derivative [Line Items]
Gain (loss) on hedges	1	(7)	0	(30)
Cash Flow Hedging | Energy-related derivatives | Operating Expense
Derivative [Line Items]
Gain (loss) on hedges	0	0	0	(1)
Cash Flow Hedging | Interest rate derivatives | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(3)	(4)	(6)	(8)
Cash Flow Hedging | Foreign currency derivatives | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(2)	(3)	(5)	(6)
Cash Flow Hedging | Foreign currency derivatives | Other Income (Expense)
Derivative [Line Items]
Gain (loss) on hedges	45	(5)	67	(17)
Fair Value Hedging | Interest rate derivatives | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	29	0	69	(31)
Fair Value Hedging | Foreign currency derivatives
Derivative [Line Items]
Amount excluded from effectiveness testing recognized in earnings	3	(4)	(13)	(4)
Fair Value Hedging | Foreign currency derivatives | Other Income (Expense)
Derivative [Line Items]
Gain (loss) on hedges	115	(18)	155	21
SOUTHERN POWER CO | Cash Flow Hedging | Energy-related derivatives | Cost of Goods and Services Sold | Fuel
Derivative [Line Items]
Gain (loss) on hedges	0	(1)	1	(2)
SOUTHERN POWER CO | Cash Flow Hedging | Foreign currency derivatives | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	(2)	(3)	(5)	(6)
SOUTHERN POWER CO | Cash Flow Hedging | Foreign currency derivatives | Other Income (Expense)
Derivative [Line Items]
Gain (loss) on hedges	45	(5)	67	(17)
SOUTHERN Co GAS | Cash Flow Hedging | Energy-related derivatives | Operating Expense
Derivative [Line Items]
Gain (loss) on hedges	0	0	0	(1)
SOUTHERN Co GAS | Cash Flow Hedging | Energy-related derivatives | Cost of Sales | Natural gas
Derivative [Line Items]
Gain (loss) on hedges	1	(7)	0	(30)
SOUTHERN Co GAS | Fair Value Hedging | Interest rate derivatives | Interest Expense
Derivative [Line Items]
Gain (loss) on hedges	$ 3	$ (6)	$ 21	$ (10)