Financing and Leases - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2023	Aug. 01, 2023	Jul. 31, 2023	Jun. 30, 2023	May 31, 2023	Apr. 30, 2023
Debt Instrument [Line Items]
Expires, 2028	$ 6,400
Line of credit facility, maximum borrowing capacity	7,605
Variable rate pollution control revenue bonds outstanding	1,700
Southern Company and Southern Power
Debt Instrument [Line Items]
Expires, 2028	2,450				$ 2,450
Southern Company parent
Debt Instrument [Line Items]
Expires, 2028	1,850				1,850
Line of credit facility, maximum borrowing capacity	2,000			$ 150
SOUTHERN POWER CO
Debt Instrument [Line Items]
Expires, 2028	600				600
Line of credit facility, maximum borrowing capacity	600
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Expires, 2028	0
Line of credit facility, maximum borrowing capacity	275				150
Variable rate pollution control revenue bonds outstanding	69
Nicor Gas
Debt Instrument [Line Items]
Expires, 2028	700
Line of credit facility, maximum borrowing capacity					$ 100	$ 250
ALABAMA POWER CO
Debt Instrument [Line Items]
Expires, 2028	700
Line of credit facility, maximum borrowing capacity	1,350	$ 650	$ 550
Variable rate pollution control revenue bonds outstanding	818
Fixed rate pollution control revenue bonds outstanding	120
GEORGIA POWER CO
Debt Instrument [Line Items]
Expires, 2028	1,750
Line of credit facility, maximum borrowing capacity	1,750
Variable rate pollution control revenue bonds outstanding	819
Fixed rate pollution control revenue bonds outstanding	$ 325