Consolidated Entities and Equity Method Investments - Schedule of Earnings (Loss) from Equity Method Investments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	$ 33	$ 31	$ 76	$ 107
SOUTHERN Co GAS
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	31	34	93	110
SOUTHERN Co GAS | SNG
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	31	34	93	110
Southern Holdings Company
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	$ 0	$ 0	$ (20)	$ 0