RETIREMENT BENEFITS - Amounts Recognized in Balance Sheets and Amounts in AOCI (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	$ 6,264	$ 5,918
Other current liabilities	(1,029)	(787)
Employee benefit obligations	(1,115)	(1,238)
Other regulatory liabilities, deferred	(715)	(733)
Regulatory asset	66	216
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	2,079	2,290
Other regulatory assets, deferred	2,960	2,455
Other current liabilities	(64)	(56)
Employee benefit obligations	(649)	(618)
Other regulatory liabilities, deferred	(47)	(85)
AOCI	79	24
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension and other postretirement benefit costs	0	0
Other regulatory assets, deferred	23	34
Other current liabilities	(6)	(6)
Employee benefit obligations	(285)	(437)
Other regulatory liabilities, deferred	(231)	(170)
AOCI	(9)	(4)
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension and other postretirement benefit costs	659	657
Other regulatory assets, deferred	1,858	2,107
Other current liabilities	(191)	(91)
Employee benefit obligations	(155)	(145)
Other regulatory liabilities, deferred	(291)	(315)
Regulatory asset	76	97
Alabama Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	585	629
Other regulatory assets, deferred	821	679
Other current liabilities	(11)	(10)
Employee benefit obligations	(106)	(98)
Other regulatory liabilities, deferred	0	0
AOCI	0	0
Alabama Power | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension and other postretirement benefit costs	74	28
Other regulatory assets, deferred	0	0
Other current liabilities	0	0
Employee benefit obligations	0	0
Other regulatory liabilities, deferred	(48)	(21)
AOCI	0	0
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	2,890	2,522
Other current liabilities	(365)	(286)
Employee benefit obligations	(248)	(318)
Regulatory asset		83
Georgia Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	706	738
Other regulatory assets, deferred	1,051	887
Other current liabilities	(13)	(12)
Employee benefit obligations	(131)	(121)
Other regulatory liabilities, deferred	0	0
AOCI	0	0
Georgia Power | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension and other postretirement benefit costs	0	0
Other regulatory assets, deferred	11	19
Other current liabilities	0	0
Employee benefit obligations	(79)	(146)
Other regulatory liabilities, deferred	(85)	(58)
AOCI	0	0
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	285	249
Other current liabilities	(90)	(85)
Employee benefit obligations	(67)	(69)
Other regulatory liabilities, deferred	(92)	(96)
Regulatory asset	44	36
Mississippi Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	99	108
Other regulatory assets, deferred	152	123
Other current liabilities	(2)	(2)
Employee benefit obligations	(27)	(26)
Other regulatory liabilities, deferred	0	0
AOCI	0	0
Mississippi Power | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension and other postretirement benefit costs	0	0
Other regulatory assets, deferred	0	0
Other current liabilities	0	0
Employee benefit obligations	(32)	(35)
Other regulatory liabilities, deferred	(10)	(9)
AOCI	0	0
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Other current liabilities	(97)	(83)
Southern Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	31	37
Other regulatory assets, deferred	0	0
Other current liabilities	(2)	(2)
Employee benefit obligations	(21)	(20)
Other regulatory liabilities, deferred	0	0
AOCI	20	11
Southern Power | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension and other postretirement benefit costs	0	0
Other regulatory assets, deferred	0	0
Other current liabilities	(1)	(1)
Employee benefit obligations	(8)	(8)
Other regulatory liabilities, deferred	0	0
AOCI	1	0
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	504	497
Other current liabilities	(232)	(254)
Employee benefit obligations	(110)	(120)
Southern Company Gas | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs	158	183
Other regulatory assets, deferred	143	111
Other current liabilities	(3)	(3)
Employee benefit obligations	(58)	(42)
Other regulatory liabilities, deferred	0	0
AOCI	(45)	(75)
Regulatory asset	173	190
Southern Company Gas | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension and other postretirement benefit costs	0	0
Other regulatory assets, deferred	0	0
Other current liabilities	0	0
Employee benefit obligations	(44)	(66)
Other regulatory liabilities, deferred	(68)	(58)
AOCI	(10)	(2)
Regulatory asset	$ 24	$ 32