RETIREMENT BENEFITS - Regulatory Assets (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	$ 6,523	$ 5,833
Regulatory asset	66	216
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	2,720	2,340
Regulatory asset	76	97
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	5,090	4,663
Regulatory asset		83
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	90	4
Regulatory asset	44	36
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	(2,225)	(1,891)
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	2,913	2,371
Pension plans | Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	821	679
Pension plans | Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	1,051	887
Pension plans | Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	152	123
Pension plans | Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	143	111
Regulatory asset	173	190
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	203	136
Other Postretirement Benefits Plan | Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	48	21
Other Postretirement Benefits Plan | Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	74	39
Other Postretirement Benefits Plan | Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	10	(9)
Other Postretirement Benefits Plan | Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	68	58
Regulatory asset	24	32
Prior Service Cost | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	9	10
Prior Service Cost | Pension plans | Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	4	4
Prior Service Cost | Pension plans | Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	6	7
Prior Service Cost | Pension plans | Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	1	1
Prior Service Cost | Pension plans | Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	(7)	(9)
Prior Service Cost | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	13	14
Prior Service Cost | Other Postretirement Benefits Plan | Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	4	4
Prior Service Cost | Other Postretirement Benefits Plan | Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	5	6
Prior Service Cost | Other Postretirement Benefits Plan | Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	1	1
Prior Service Cost | Other Postretirement Benefits Plan | Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	0	1
Net Actuarial Gain (Loss) | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	2,904	2,361
Net Actuarial Gain (Loss) | Pension plans | Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	817	675
Net Actuarial Gain (Loss) | Pension plans | Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	1,045	880
Net Actuarial Gain (Loss) | Pension plans | Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	151	122
Net Actuarial Gain (Loss) | Pension plans | Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	100	66
Net Actuarial Gain (Loss) | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	216	150
Net Actuarial Gain (Loss) | Other Postretirement Benefits Plan | Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	52	25
Net Actuarial Gain (Loss) | Other Postretirement Benefits Plan | Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	79	45
Net Actuarial Gain (Loss) | Other Postretirement Benefits Plan | Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	11	10
Net Actuarial Gain (Loss) | Other Postretirement Benefits Plan | Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	64	64
Regulatory Amortization | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	0	0
Regulatory Amortization | Pension plans | Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	0	0
Regulatory Amortization | Pension plans | Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	0	0
Regulatory Amortization | Pension plans | Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	0	0
Regulatory Amortization | Pension plans | Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	50	54
Regulatory Amortization | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	0	0
Regulatory Amortization | Other Postretirement Benefits Plan | Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	0	0
Regulatory Amortization | Other Postretirement Benefits Plan | Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	0	0
Regulatory Amortization | Other Postretirement Benefits Plan | Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	0	0
Regulatory Amortization | Other Postretirement Benefits Plan | Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Net regulatory assets	$ (4)	$ 5