Revenue from Contracts with Customers and Lease Income - Schedule of Contract Balances (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Disaggregation of Revenue [Line Items]
Accounts Receivable	$ 2,942	$ 3,048
Contract Assets	443	323
Contract Liabilities	185	140
ALABAMA POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	827	783
Contract Assets	8	3
Contract Liabilities	15	11
GEORGIA POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	1,390	1,244
Contract Assets	283	184
Contract Liabilities	72	34
MISSISSIPPI POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	137	113
Contract Assets	0	0
Contract Liabilities	2	0
SOUTHERN POWER CO
Disaggregation of Revenue [Line Items]
Accounts Receivable	106	106
Contract Assets	0	0
Contract Liabilities	2	2
SOUTHERN Co GAS
Disaggregation of Revenue [Line Items]
Accounts Receivable	331	660
Contract Assets	74	72
Contract Liabilities	$ 0	$ 3