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Retirement Benefits (Details) - USD ($)
 3 Months Ended 6 Months Ended
Jun. 30, 2024
Jun. 30, 2023
Jun. 30, 2024
Jun. 30, 2023
Pension Plans        
Defined Benefit Plan Disclosure [Line Items]        
Defined benefit plan, expected future employer contributions, remainder of fiscal year $ 0   $ 0  
Pension Plans and Postretirement Plans        
Service cost 73,000,000 $ 69,000,000 146,000,000 $ 138,000,000
Interest cost 158,000,000 157,000,000 317,000,000 313,000,000
Expected return on plan assets (315,000,000) (308,000,000) (631,000,000) (615,000,000)
Amortization:        
Prior service costs 0 0 0 0
Regulatory asset 0 0 0 0
Net loss 13,000,000 8,000,000 27,000,000 16,000,000
Net periodic pension income (71,000,000) (74,000,000) (141,000,000) (148,000,000)
Pension Plans | ALABAMA POWER CO        
Pension Plans and Postretirement Plans        
Service cost 17,000,000 16,000,000 34,000,000 32,000,000
Interest cost 37,000,000 36,000,000 74,000,000 72,000,000
Expected return on plan assets (76,000,000) (74,000,000) (153,000,000) (148,000,000)
Amortization:        
Prior service costs 0 0 0 0
Regulatory asset 0 0 0 0
Net loss 4,000,000 3,000,000 8,000,000 5,000,000
Net periodic pension income (18,000,000) (19,000,000) (37,000,000) (39,000,000)
Pension Plans | GEORGIA POWER CO        
Pension Plans and Postretirement Plans        
Service cost 17,000,000 17,000,000 35,000,000 34,000,000
Interest cost 48,000,000 47,000,000 96,000,000 95,000,000
Expected return on plan assets (98,000,000) (96,000,000) (197,000,000) (192,000,000)
Amortization:        
Prior service costs 1,000,000 1,000,000 1,000,000 1,000,000
Regulatory asset 0 0 0 0
Net loss 4,000,000 3,000,000 9,000,000 6,000,000
Net periodic pension income (28,000,000) (28,000,000) (56,000,000) (56,000,000)
Pension Plans | MISSISSIPPI POWER CO        
Pension Plans and Postretirement Plans        
Service cost 3,000,000 3,000,000 6,000,000 6,000,000
Interest cost 7,000,000 7,000,000 14,000,000 14,000,000
Expected return on plan assets (15,000,000) (14,000,000) (29,000,000) (28,000,000)
Amortization:        
Prior service costs 0 0 0 0
Regulatory asset 0 0 0 0
Net loss 2,000,000 0 2,000,000 0
Net periodic pension income (3,000,000) (4,000,000) (7,000,000) (8,000,000)
Pension Plans | SOUTHERN POWER CO        
Pension Plans and Postretirement Plans        
Service cost 1,000,000 1,000,000 3,000,000 3,000,000
Interest cost 2,000,000 2,000,000 4,000,000 4,000,000
Expected return on plan assets (4,000,000) (4,000,000) (8,000,000) (8,000,000)
Amortization:        
Prior service costs 0 0 0 0
Regulatory asset 0 0 0 0
Net loss 1,000,000 0 1,000,000 0
Net periodic pension income 0 (1,000,000) 0 (1,000,000)
Pension Plans | SOUTHERN Co GAS        
Pension Plans and Postretirement Plans        
Service cost 7,000,000 6,000,000 14,000,000 12,000,000
Interest cost 11,000,000 11,000,000 21,000,000 21,000,000
Expected return on plan assets (21,000,000) (22,000,000) (43,000,000) (44,000,000)
Amortization:        
Prior service costs (1,000,000) (1,000,000) (1,000,000) (1,000,000)
Regulatory asset 4,000,000 4,000,000 8,000,000 8,000,000
Net loss 0 (1,000,000) 0 (2,000,000)
Net periodic pension income 0 (3,000,000) (1,000,000) (6,000,000)
Postretirement Benefits        
Pension Plans and Postretirement Plans        
Service cost 3,000,000 3,000,000 7,000,000 7,000,000
Interest cost 17,000,000 17,000,000 33,000,000 35,000,000
Expected return on plan assets (22,000,000) (20,000,000) (44,000,000) (41,000,000)
Amortization:        
Prior service costs   1,000,000 1,000,000 1,000,000
Regulatory asset 0 0 0 0
Net loss (4,000,000) (3,000,000) (8,000,000) (6,000,000)
Net periodic pension income (6,000,000) (2,000,000) (11,000,000) (4,000,000)
Postretirement Benefits | ALABAMA POWER CO        
Pension Plans and Postretirement Plans        
Service cost 1,000,000 1,000,000 2,000,000 2,000,000
Interest cost 4,000,000 4,000,000 8,000,000 8,000,000
Expected return on plan assets (8,000,000) (9,000,000) (17,000,000) (17,000,000)
Amortization:        
Prior service costs   0 0 0
Regulatory asset 0 0 0 0
Net loss (2,000,000) 0 (2,000,000) (1,000,000)
Net periodic pension income (5,000,000) (4,000,000) (9,000,000) (8,000,000)
Postretirement Benefits | GEORGIA POWER CO        
Pension Plans and Postretirement Plans        
Service cost 1,000,000 1,000,000 2,000,000 2,000,000
Interest cost 5,000,000 7,000,000 11,000,000 13,000,000
Expected return on plan assets (8,000,000) (8,000,000) (16,000,000) (15,000,000)
Amortization:        
Prior service costs   0 0 0
Regulatory asset 0 0 0 0
Net loss 0 (1,000,000) (1,000,000) (2,000,000)
Net periodic pension income (2,000,000) (1,000,000) (4,000,000) (2,000,000)
Postretirement Benefits | MISSISSIPPI POWER CO        
Pension Plans and Postretirement Plans        
Service cost 0 0 0 0
Interest cost 0 1,000,000 1,000,000 2,000,000
Expected return on plan assets 0 0 0 (1,000,000)
Amortization:        
Prior service costs   0 0 0
Regulatory asset 0 0 0 0
Net loss 0 0 (1,000,000) 0
Net periodic pension income 0 1,000,000 0 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
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 0 0
Interest cost 2,000,000 2,000,000 4,000,000 4,000,000
Expected return on plan assets (2,000,000) (2,000,000) (4,000,000) (3,000,000)
Amortization:        
Prior service costs   0 0 0
Regulatory asset 2,000,000 2,000,000 3,000,000 3,000,000
Net loss (1,000,000) (1,000,000) (3,000,000) (2,000,000)
Net periodic pension income $ 1,000,000 $ 1,000,000 $ 0 $ 2,000,000