Financing - Schedule of Credit Arrangements (Details) - USD ($) $ in Millions	Mar. 31, 2026	Feb. 20, 2026	Mar. 31, 2025
Line of Credit Facility [Line Items]
2026	$ 45
2028	500
2029	775
2030	2,300
2031	5,300
Total	8,920
Unused	8,909
Expires within One Year	45
Southern Company parent
Line of Credit Facility [Line Items]
2026	0
2028	500
2029	0
2030	0
2031	2,500
Total	3,000
Unused	2,999
Expires within One Year	0
ALABAMA POWER CO
Line of Credit Facility [Line Items]
2026	15
2028	0
2029	650
2030	700
2031	0
Total	1,365
Unused	1,365
Expires within One Year	15
ALABAMA POWER CO | FFB Credit Facility
Line of Credit Facility [Line Items]
Total		$ 4,100
GEORGIA POWER CO
Line of Credit Facility [Line Items]
2026	0
2028	0
2029	0
2030	0
2031	2,050
Total	2,050
Unused	2,042
Expires within One Year	0
GEORGIA POWER CO | Uncommited Letter Of Credit Facility
Line of Credit Facility [Line Items]
Letters of credit outstanding	26
GEORGIA POWER CO | FFB Credit Facility
Line of Credit Facility [Line Items]
Total		$ 22,400
MISSISSIPPI POWER CO
Line of Credit Facility [Line Items]
2026	0
2028	0
2029	125
2030	0
2031	150
Total	275
Unused	275
Expires within One Year	0
SOUTHERN POWER CO
Line of Credit Facility [Line Items]
2026	0
2028	0
2029	0
2030	0
2031	600
Total	600
Unused	600
Expires within One Year	0
SOUTHERN POWER CO | Continuing Letter of Credit Facility A
Line of Credit Facility [Line Items]
Total	75
Unused	17
SOUTHERN POWER CO | Continuing Letter of Credit Facility B
Line of Credit Facility [Line Items]
Total	100
Unused	4
SOUTHERN POWER CO | Uncommited Letter Of Credit Facility
Line of Credit Facility [Line Items]
Letters of credit outstanding	23
SOUTHERN Co GAS
Line of Credit Facility [Line Items]
2026	0
2028	0
2029	0
2030	1,600
2031	0
Total	1,600
Unused	1,598
Expires within One Year	0
SEGCO
Line of Credit Facility [Line Items]
2026	30
2028	0
2029	0
2030	0
2031	0
Total	30
Unused	30
Expires within One Year	30
Southern Company, Southern Power, And Mississippi Power
Line of Credit Facility [Line Items]
Total			$ 3,250
Alabama Property Company
Line of Credit Facility [Line Items]
2026	15
Unused	15
Southern Company Gas Capital
Line of Credit Facility [Line Items]
2031	800
Nicor Gas
Line of Credit Facility [Line Items]
2031	$ 800