Revenue from Contracts with Customers and Lease Income - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2025	Sep. 30, 2025	Dec. 31, 2024
Disaggregation of Revenue [Line Items]
Contract liabilities	$ 185	$ 185	$ 140
Contract assets	443	443	323
Revenue from contracts with customers recognized	20	92
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Contract liabilities	72	72	34
Contract assets	283	283	184
Revenue from contracts with customers recognized	8	24
SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Contract liabilities	0	0	3
Contract assets	74	74	72
Revenue from contracts with customers recognized	0	0
ALABAMA POWER CO
Disaggregation of Revenue [Line Items]
Contract liabilities	15	15	11
Contract assets	8	8	3
Revenue from contracts with customers recognized	0	0
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Contract liabilities	2	2	0
Contract assets	0	0	0
Revenue from contracts with customers recognized	0	0
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Contract liabilities	2	2	2
Contract assets	0	0	0
Revenue from contracts with customers recognized	0	$ 0
Retail Customer Fixed Bill Programs | GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Contract term		1 year
Energy Efficiency Enhancement And Upgrade | SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Contract liabilities	68	$ 68
Unregulated Distributed Generation
Disaggregation of Revenue [Line Items]
Contract liabilities	96	96	95
Contract assets	$ 77	$ 77	$ 67