Financing - Bank Credit Agreements Narrative (Details) - USD ($) $ in Millions	1 Months Ended
	Mar. 31, 2025	Sep. 30, 2025	Feb. 28, 2025
Debt Instrument [Line Items]
2030		$ 7,600
Line of credit facility, maximum borrowing capacity		8,920
Variable rate pollution control revenue bonds outstanding		1,500
2027		625
2029		650
2026		45
Southern Company, Southern Power, And Mississippi Power
Debt Instrument [Line Items]
2030		3,250
Line of credit facility, maximum borrowing capacity	$ 3,250		$ 2,450
Southern Company parent
Debt Instrument [Line Items]
2030		2,500
Line of credit facility, maximum borrowing capacity		3,000
2028			150
2027		500
2029		0
2026		0
SOUTHERN POWER CO
Debt Instrument [Line Items]
2030		600
Line of credit facility, maximum borrowing capacity		600
2027		0
2029		0
2026		0
MISSISSIPPI POWER CO
Debt Instrument [Line Items]
2030		150
Line of credit facility, maximum borrowing capacity		275
Decrease of line of credit	150
Variable rate pollution control revenue bonds outstanding		58
2027		125
2029		0
2026		0
GEORGIA POWER CO
Debt Instrument [Line Items]
2030		2,050	1,750
Line of credit facility, maximum borrowing capacity		2,050
Decrease of line of credit	300
Variable rate pollution control revenue bonds outstanding		667
Fixed rate pollution control revenue bonds outstanding		384
2027		0
2029		0
2026		0
SOUTHERN Co GAS
Debt Instrument [Line Items]
2030		1,600
Line of credit facility, maximum borrowing capacity		1,600
2027		0
2029		0	$ 1,500
2026		0
Nicor Gas
Debt Instrument [Line Items]
2030	800	800
Decrease of line of credit	100
ALABAMA POWER CO
Debt Instrument [Line Items]
2030		700
Line of credit facility, maximum borrowing capacity		1,365
Variable rate pollution control revenue bonds outstanding		796
Fixed rate pollution control revenue bonds outstanding		280
2027		0
2029		650
2026		15
Southern Company Gas Capital
Debt Instrument [Line Items]
2030	$ 800	800
SEGCO
Debt Instrument [Line Items]
2030		0
Line of credit facility, maximum borrowing capacity		30
2027		0
2029		0
2026		$ 30