v3.23.3
Retirement Benefits (Details) - USD ($)
 3 Months Ended 9 Months Ended
Sep. 30, 2023
Sep. 30, 2022
Sep. 30, 2023
Sep. 30, 2022
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 69,000,000 $ 103,000,000 207,000,000 $ 309,000,000
Interest cost 156,000,000 102,000,000 469,000,000 306,000,000
Expected return on plan assets (307,000,000) (316,000,000) (922,000,000) (949,000,000)
Amortization:        
Prior service costs 0 0 0 0
Regulatory asset 0 0 0 0
Net (gain) loss 8,000,000 60,000,000 24,000,000 180,000,000
Net periodic pension income (74,000,000) (51,000,000) (222,000,000) (154,000,000)
Pension Plans | ALABAMA POWER CO        
Pension Plans and Postretirement Plans        
Service cost 16,000,000 25,000,000 48,000,000 74,000,000
Interest cost 37,000,000 24,000,000 109,000,000 72,000,000
Expected return on plan assets (75,000,000) (77,000,000) (223,000,000) (229,000,000)
Amortization:        
Prior service costs 0 0 0 0
Regulatory asset 0 0 0 0
Net (gain) loss 2,000,000 16,000,000 7,000,000 47,000,000
Net periodic pension income (20,000,000) (12,000,000) (59,000,000) (36,000,000)
Pension Plans | GEORGIA POWER CO        
Pension Plans and Postretirement Plans        
Service cost 17,000,000 26,000,000 51,000,000 78,000,000
Interest cost 48,000,000 31,000,000 143,000,000 92,000,000
Expected return on plan assets (97,000,000) (99,000,000) (289,000,000) (298,000,000)
Amortization:        
Prior service costs 0 0 1,000,000 1,000,000
Regulatory asset 0 0 0 0
Net (gain) loss 4,000,000 18,000,000 10,000,000 55,000,000
Net periodic pension income (28,000,000) (24,000,000) (84,000,000) (72,000,000)
Pension Plans | MISSISSIPPI POWER CO        
Pension Plans and Postretirement Plans        
Service cost 2,000,000 5,000,000 8,000,000 13,000,000
Interest cost 7,000,000 5,000,000 21,000,000 14,000,000
Expected return on plan assets (13,000,000) (15,000,000) (41,000,000) (44,000,000)
Amortization:        
Prior service costs 0 0 0 0
Regulatory asset 0 0 0 0
Net (gain) loss 1,000,000 2,000,000 1,000,000 9,000,000
Net periodic pension income (3,000,000) (3,000,000) (11,000,000) (8,000,000)
Pension Plans | SOUTHERN POWER CO        
Pension Plans and Postretirement Plans        
Service cost 2,000,000 2,000,000 5,000,000 7,000,000
Interest cost 2,000,000 2,000,000 6,000,000 5,000,000
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 (gain) loss 0 1,000,000 0 2,000,000
Net periodic pension income 0 1,000,000 (1,000,000) 2,000,000
Pension Plans | SOUTHERN Co GAS        
Pension Plans and Postretirement Plans        
Service cost 6,000,000 9,000,000 18,000,000 26,000,000
Interest cost 11,000,000 7,000,000 32,000,000 21,000,000
Expected return on plan assets (22,000,000) (22,000,000) (65,000,000) (68,000,000)
Amortization:        
Prior service costs (1,000,000) (1,000,000) (2,000,000) (2,000,000)
Regulatory asset 4,000,000 3,000,000 11,000,000 11,000,000
Net (gain) loss (1,000,000) 2,000,000 (3,000,000) 5,000,000
Net periodic pension income (3,000,000) (2,000,000) (9,000,000) (7,000,000)
Postretirement Benefits        
Pension Plans and Postretirement Plans        
Service cost 4,000,000 6,000,000 11,000,000 17,000,000
Interest cost 18,000,000 10,000,000 53,000,000 31,000,000
Expected return on plan assets (21,000,000) (20,000,000) (62,000,000) (60,000,000)
Amortization:        
Prior service costs 0 (1,000,000) 1,000,000 (1,000,000)
Regulatory asset 0 0 0 0
Net (gain) loss (4,000,000) 1,000,000 (10,000,000) 1,000,000
Net periodic pension income (3,000,000) (4,000,000) (7,000,000) (12,000,000)
Postretirement Benefits | ALABAMA POWER CO        
Pension Plans and Postretirement Plans        
Service cost 1,000,000 2,000,000 3,000,000 5,000,000
Interest cost 5,000,000 3,000,000 13,000,000 8,000,000
Expected return on plan assets (9,000,000) (9,000,000) (26,000,000) (25,000,000)
Amortization:        
Prior service costs 0 0 0 0
Regulatory asset 0 0 0 0
Net (gain) loss (1,000,000) 0 (2,000,000) 0
Net periodic pension income (4,000,000) (4,000,000) (12,000,000) (12,000,000)
Postretirement Benefits | GEORGIA POWER CO        
Pension Plans and Postretirement Plans        
Service cost 1,000,000 2,000,000 3,000,000 5,000,000
Interest cost 6,000,000 4,000,000 19,000,000 11,000,000
Expected return on plan assets (7,000,000) (8,000,000) (22,000,000) (21,000,000)
Amortization:        
Prior service costs 1,000,000 0 1,000,000 0
Regulatory asset 0 0 0 0
Net (gain) loss (1,000,000) 0 (3,000,000) 1,000,000
Net periodic pension income 0 (2,000,000) (2,000,000) (4,000,000)
Postretirement Benefits | MISSISSIPPI POWER CO        
Pension Plans and Postretirement Plans        
Service cost 0 1,000,000 0 1,000,000
Interest cost 1,000,000 0 2,000,000 1,000,000
Expected return on plan assets (1,000,000) 0 (1,000,000) (1,000,000)
Amortization:        
Prior service costs 0 0 0 0
Regulatory asset 0 0 0 0
Net (gain) loss 0 0 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 1,000,000 0 1,000,000
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 (gain) loss 0 0 0 0
Net periodic pension income 0 1,000,000 0 1,000,000
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 1,000,000 6,000,000 4,000,000
Expected return on plan assets (2,000,000) (2,000,000) (5,000,000) (6,000,000)
Amortization:        
Prior service costs 0 0 0 0
Regulatory asset 2,000,000 2,000,000 5,000,000 5,000,000
Net (gain) loss (1,000,000) (1,000,000) (3,000,000) (2,000,000)
Net periodic pension income $ 1,000,000 $ 0 $ 4,000,000 $ 2,000,000