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Retirement Benefits (Details) - USD ($)
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Dec. 31, 2025
Pension Plans          
Pension Plans and Postretirement Plans          
Service cost $ 66,000,000 $ 73,000,000 $ 198,000,000 $ 219,000,000  
Interest cost 166,000,000 159,000,000 498,000,000 476,000,000  
Expected return on plan assets (320,000,000) (316,000,000) (960,000,000) (947,000,000)  
Amortization:          
Prior service costs 0 0 0 0  
Regulatory asset 0 0 0 0  
Net loss 9,000,000 14,000,000 28,000,000 41,000,000  
Net periodic pension income (79,000,000) (70,000,000) (236,000,000) (211,000,000)  
Pension Plans | Scenario, Forecast          
Defined Benefit Plan Disclosure [Line Items]          
Defined benefit plan, expected future employer contributions, remainder of fiscal year         $ 0
Pension Plans | ALABAMA POWER CO          
Pension Plans and Postretirement Plans          
Service cost 15,000,000 17,000,000 45,000,000 51,000,000  
Interest cost 39,000,000 37,000,000 116,000,000 111,000,000  
Expected return on plan assets (78,000,000) (77,000,000) (234,000,000) (230,000,000)  
Amortization:          
Prior service costs 0 0 0 0  
Regulatory asset 0 0 0 0  
Net loss 2,000,000 4,000,000 8,000,000 12,000,000  
Net periodic pension income (22,000,000) (19,000,000) (65,000,000) (56,000,000)  
Pension Plans | GEORGIA POWER CO          
Pension Plans and Postretirement Plans          
Service cost 16,000,000 18,000,000 47,000,000 53,000,000  
Interest cost 49,000,000 47,000,000 147,000,000 143,000,000  
Expected return on plan assets (100,000,000) (99,000,000) (298,000,000) (296,000,000)  
Amortization:          
Prior service costs 0 0 1,000,000 1,000,000  
Regulatory asset 0 0 0 0  
Net loss 5,000,000 6,000,000 12,000,000 15,000,000  
Net periodic pension income (30,000,000) (28,000,000) (91,000,000) (84,000,000)  
Pension Plans | MISSISSIPPI POWER CO          
Pension Plans and Postretirement Plans          
Service cost 3,000,000 3,000,000 8,000,000 9,000,000  
Interest cost 7,000,000 7,000,000 22,000,000 21,000,000  
Expected return on plan assets (15,000,000) (14,000,000) (44,000,000) (43,000,000)  
Amortization:          
Prior service costs 0 0 0 0  
Regulatory asset 0 0 0 0  
Net loss 2,000,000 0 3,000,000 2,000,000  
Net periodic pension income (3,000,000) (4,000,000) (11,000,000) (11,000,000)  
Pension Plans | SOUTHERN POWER CO          
Pension Plans and Postretirement Plans          
Service cost 1,000,000 2,000,000 4,000,000 5,000,000  
Interest cost 2,000,000 2,000,000 7,000,000 6,000,000  
Expected return on plan assets (4,000,000) (4,000,000) (12,000,000) (12,000,000)  
Amortization:          
Prior service costs 0 0 0 0  
Regulatory asset 0 0 0 0  
Net loss 1,000,000 (1,000,000) 0 0  
Net periodic pension income 0 (1,000,000) (1,000,000) (1,000,000)  
Pension Plans | SOUTHERN Co GAS          
Pension Plans and Postretirement Plans          
Service cost 7,000,000 7,000,000 20,000,000 21,000,000  
Interest cost 11,000,000 11,000,000 33,000,000 32,000,000  
Expected return on plan assets (22,000,000) (21,000,000) (65,000,000) (64,000,000)  
Amortization:          
Prior service costs (1,000,000) (1,000,000) (2,000,000) (2,000,000)  
Regulatory asset 4,000,000 4,000,000 11,000,000 11,000,000  
Net loss 0 0 (1,000,000) 0  
Net periodic pension income (1,000,000) 0 (4,000,000) (2,000,000)  
Postretirement Benefits          
Pension Plans and Postretirement Plans          
Service cost 4,000,000 4,000,000 10,000,000 11,000,000  
Interest cost 17,000,000 16,000,000 52,000,000 49,000,000  
Expected return on plan assets (23,000,000) (22,000,000) (68,000,000) (66,000,000)  
Amortization:          
Prior service costs 1,000,000 1,000,000 2,000,000 2,000,000  
Regulatory asset 0 0 0 0  
Net loss (4,000,000) (4,000,000) (11,000,000) (12,000,000)  
Net periodic pension income (5,000,000) (5,000,000) (15,000,000) (16,000,000)  
Postretirement Benefits | ALABAMA POWER CO          
Pension Plans and Postretirement Plans          
Service cost 1,000,000 1,000,000 3,000,000 3,000,000  
Interest cost 5,000,000 4,000,000 13,000,000 12,000,000  
Expected return on plan assets (8,000,000) (9,000,000) (26,000,000) (26,000,000)  
Amortization:          
Prior service costs 0 0 0 0  
Regulatory asset 0 0 0 0  
Net loss (2,000,000) 0 (2,000,000) (2,000,000)  
Net periodic pension income (4,000,000) (4,000,000) (12,000,000) (13,000,000)  
Postretirement Benefits | GEORGIA POWER CO          
Pension Plans and Postretirement Plans          
Service cost 1,000,000 1,000,000 3,000,000 3,000,000  
Interest cost 6,000,000 6,000,000 19,000,000 17,000,000  
Expected return on plan assets (9,000,000) (8,000,000) (25,000,000) (24,000,000)  
Amortization:          
Prior service costs 1,000,000 1,000,000 1,000,000 1,000,000  
Regulatory asset 0 0 0 0  
Net loss 0 (3,000,000) (2,000,000) (4,000,000)  
Net periodic pension income (1,000,000) (3,000,000) (4,000,000) (7,000,000)  
Postretirement Benefits | MISSISSIPPI POWER CO          
Pension Plans and Postretirement Plans          
Service cost 0 0 0 0  
Interest cost 1,000,000 1,000,000 2,000,000 2,000,000  
Expected return on plan assets (1,000,000) (1,000,000) (1,000,000) (1,000,000)  
Amortization:          
Prior service costs 0 0 0 0  
Regulatory asset 0 0 0 0  
Net loss 0 1,000,000 0 0  
Net periodic pension income 0 1,000,000 1,000,000 1,000,000  
Postretirement Benefits | SOUTHERN POWER CO          
Pension Plans and Postretirement Plans          
Service cost 0 0 0 0  
Interest cost 0 0 0 0  
Expected return on plan assets 0 0 0 0  
Amortization:          
Prior service costs 0 0 0 0  
Regulatory asset 0 0 0 0  
Net loss 0 0 0 0  
Net periodic pension income 0 0 0 0  
Postretirement Benefits | SOUTHERN Co GAS          
Pension Plans and Postretirement Plans          
Service cost 0 0 1,000,000 1,000,000  
Interest cost 2,000,000 2,000,000 6,000,000 6,000,000  
Expected return on plan assets (2,000,000) (2,000,000) (7,000,000) (6,000,000)  
Amortization:          
Prior service costs 0 0 0 0  
Regulatory asset 1,000,000 2,000,000 5,000,000 5,000,000  
Net loss (2,000,000) (1,000,000) (6,000,000) (4,000,000)  
Net periodic pension income $ (1,000,000) $ 1,000,000 $ (1,000,000) $ 2,000,000