RETIREMENT BENEFITS - Components of Net Periodic Benefit Cost and Estimated Future Benefit Payments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension plans
Components of net periodic
Service cost	$ 275	$ 412	$ 434
Interest cost	626	408	346
Expected return on plan assets	(1,229)	(1,265)	(1,191)
Recognized net (gain) loss	32	240	314
Net amortization	0	0	1
Prior service cost	0	0	0
Total change	(296)	(205)	(96)
Benefit payments:
2024	748
2025	776
2026	801
2027	822
2028	840
2029 to 2033	4,417
Other Postretirement Benefits Plan
Components of net periodic
Service cost	15	23	24
Interest cost	70	42	35
Expected return on plan assets	(83)	(80)	(76)
Prior service cost	(11)	(1)	2
Total change	(9)	(16)	(15)
Benefit payments:
2024	111
2025	109
2026	108
2027	108
2028	108
2029 to 2033	523
Alabama Power | Pension plans
Components of net periodic
Service cost	64	99	102
Interest cost	145	96	82
Expected return on plan assets	(297)	(306)	(287)
Recognized net (gain) loss	9	62	82
Net amortization	1	1	1
Prior service cost	0	0	0
Total change	(78)	(48)	(20)
Benefit payments:
2024	164
2025	171
2026	177
2027	182
2028	187
2029 to 2033	988
Alabama Power | Other Postretirement Benefits Plan
Components of net periodic
Service cost	4	6	6
Interest cost	17	10	9
Expected return on plan assets	(33)	(32)	(30)
Prior service cost	(3)	0	0
Total change	(15)	(16)	(15)
Benefit payments:
2024	24
2025	24
2026	24
2027	24
2028	25
2029 to 2033	123
Georgia Power | Pension plans
Components of net periodic
Service cost	68	103	112
Interest cost	191	123	104
Expected return on plan assets	(385)	(399)	(375)
Recognized net (gain) loss	13	75	100
Net amortization	1	1	1
Prior service cost	0	0	0
Total change	(112)	(97)	(58)
Benefit payments:
2024	241
2025	248
2026	254
2027	257
2028	260
2029 to 2033	1,337
Georgia Power | Other Postretirement Benefits Plan
Components of net periodic
Service cost	4	6	7
Interest cost	25	15	12
Expected return on plan assets	(29)	(28)	(26)
Prior service cost	(3)	2	2
Total change	(3)	(5)	(5)
Benefit payments:
2024	40
2025	39
2026	38
2027	38
2028	38
2029 to 2033	188
Mississippi Power | Pension plans
Components of net periodic
Service cost	11	17	18
Interest cost	28	18	16
Expected return on plan assets	(56)	(57)	(55)
Recognized net (gain) loss	2	11	15
Net amortization	0	0	0
Prior service cost	0	0	0
Total change	(15)	(11)	(6)
Benefit payments:
2024	33
2025	34
2026	36
2027	37
2028	38
2029 to 2033	201
Mississippi Power | Other Postretirement Benefits Plan
Components of net periodic
Service cost	1	1	1
Interest cost	3	2	1
Expected return on plan assets	(3)	(2)	(1)
Prior service cost	0	0	0
Total change	1	1	1
Benefit payments:
2024	5
2025	5
2026	5
2027	5
2028	4
2029 to 2033	21
Southern Power | Pension plans
Components of net periodic
Service cost	6	9	10
Interest cost	8	6	5
Expected return on plan assets	(15)	(15)	(14)
Recognized net (gain) loss	0	2	3
Net amortization	0	0	0
Prior service cost	0	0	0
Total change	(1)	2	4
Benefit payments:
2024	7
2025	7
2026	8
2027	8
2028	7
2029 to 2033	47
Southern Power | Other Postretirement Benefits Plan
Components of net periodic
Service cost	0	0	0
Interest cost	0	0	0
Expected return on plan assets	1	1	1
Prior service cost	0	0	0
Total change	1	1	1
Benefit payments:
2024	1
2025	1
2026	1
2027	1
2028	1
2029 to 2033	1
Southern Company Gas | Pension plans
Components of net periodic
Service cost	24	34	37
Interest cost	42	28	24
Expected return on plan assets	(85)	(91)	(86)
Recognized net (gain) loss	(5)	8	13
Net amortization	15	15	15
Prior service cost	(3)	(3)	(3)
Total change	(12)	(9)	0
Benefit payments:
2024	57
2025	59
2026	60
2027	62
2028	64
2029 to 2033	336
Southern Company Gas | Other Postretirement Benefits Plan
Components of net periodic
Service cost	1	1	2
Interest cost	9	5	4
Expected return on plan assets	(10)	(9)	(10)
Prior service cost	6	6	6
Total change	6	$ 3	$ 2
Benefit payments:
2024	17
2025	17
2026	16
2027	16
2028	15
2029 to 2033	$ 64