RETIREMENT BENEFITS - Amounts Recognized in Balance Sheets and Amounts in AOCI (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	$ 5,918	$ 5,577
Other current liabilities	(965)	(872)
Employee benefit obligations	(1,238)	(1,550)
Other regulatory liabilities, deferred	(733)	(485)
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs(a)	2,290	1,657
Other regulatory assets, deferred	2,455	2,920
Other current liabilities	(56)	(55)
Employee benefit obligations	(618)	(759)
Other regulatory liabilities, deferred	(85)	(119)
AOCI	24	100
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension and other postretirement benefit costs	0	0
Other regulatory assets, deferred	34	97
Other current liabilities	(6)	(5)
Employee benefit obligations	(437)	(593)
Other regulatory liabilities, deferred	(170)	(171)
AOCI	(4)	0
Alabama Power
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension and other postretirement benefit costs	657	513
Other regulatory assets, deferred	2,107	1,807
Other current liabilities	(91)	(125)
Employee benefit obligations	(145)	(171)
Other regulatory liabilities, deferred	(315)	(210)
Alabama Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs(a)	629	464
Other regulatory assets, deferred	679	809
Other current liabilities	(10)	(9)
Employee benefit obligations	(98)	(120)
Other regulatory liabilities, deferred	0	0
AOCI	0	0
Alabama Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension and other postretirement benefit costs	28	49
Other regulatory assets, deferred	0	0
Other current liabilities	0	0
Employee benefit obligations	0	0
Other regulatory liabilities, deferred	(21)	(62)
AOCI	0	0
Georgia Power
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	2,522	1,964
Other current liabilities	(286)	(254)
Employee benefit obligations	(318)	(402)
Georgia Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs(a)	738	563
Other regulatory assets, deferred	887	971
Other current liabilities	(12)	(12)
Employee benefit obligations	(121)	(148)
Other regulatory liabilities, deferred	0	0
AOCI	0	0
Georgia Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension and other postretirement benefit costs	0	0
Other regulatory assets, deferred	19	30
Other current liabilities	0	0
Employee benefit obligations	(146)	(206)
Other regulatory liabilities, deferred	(58)	(40)
AOCI	0	0
Mississippi Power
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs(a)	109	79
Other regulatory assets, deferred	249	317
Other current liabilities	(85)	(65)
Employee benefit obligations	(69)	(88)
Other regulatory liabilities, deferred	(96)	(64)
Mississippi Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs(a)	108	78
Other regulatory assets, deferred	123	146
Other current liabilities	(2)	(2)
Employee benefit obligations	(26)	(33)
Other regulatory liabilities, deferred	0	0
AOCI	0	0
Mississippi Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension and other postretirement benefit costs	0	0
Other regulatory assets, deferred	0	2
Other current liabilities	0	0
Employee benefit obligations	(35)	(47)
Other regulatory liabilities, deferred	(9)	(1)
AOCI	0	0
Southern Power
Defined Benefit Plan Disclosure [Line Items]
Other current liabilities	(111)	(140)
Southern Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs(a)	37	20
Other regulatory assets, deferred	0	0
Other current liabilities	(2)	(2)
Employee benefit obligations	(20)	(27)
Other regulatory liabilities, deferred	0	0
AOCI	11	35
Southern Power | Other postretirement benefit plans
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)	0
Employee benefit obligations	(8)	(11)
Other regulatory liabilities, deferred	0	0
AOCI	0	2
Southern Company Gas
Defined Benefit Plan Disclosure [Line Items]
Other regulatory assets, deferred	497	689
Other current liabilities	(254)	(214)
Employee benefit obligations	(120)	(176)
Southern Company Gas | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prepaid pension costs(a)	183	175
Other regulatory assets, deferred	111	91
Other current liabilities	(3)	(2)
Employee benefit obligations	(42)	(66)
Other regulatory liabilities, deferred	0	0
AOCI	(75)	(45)
Regulatory asset	190	210
Southern Company Gas | Other postretirement benefit plans
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	(66)	(94)
Other regulatory liabilities, deferred	(58)	(34)
AOCI	(2)	(5)
Regulatory asset	$ 32	$ 40