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Financing - Bank Credit Agreements Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2026	Mar. 31, 2025
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 8,920
Variable rate pollution control revenue bonds outstanding	1,500
Southern Company, Southern Power, And Mississippi Power
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 3,250
ALABAMA POWER CO
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	1,365
Variable rate pollution control revenue bonds outstanding	796
Fixed rate pollution control revenue bonds outstanding	160
GEORGIA POWER CO
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	2,050
Variable rate pollution control revenue bonds outstanding	667
Fixed rate pollution control revenue bonds outstanding	325
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	275
Variable rate pollution control revenue bonds outstanding	$ 58

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