RETIREMENT BENEFITS - Components of Accumulated OCI and Changes in Regulatory Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 32,276	$ 32,234	$ 31,759
Total other comprehensive income (loss)	71	158	(75)
Ending balance	34,532	32,276	32,234
Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(76)
Total other comprehensive income (loss)	58
Ending balance	(18)	(76)
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	(2)	(2)
Net loss	26	102
Total AOCI	24	100
Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	10	11
Net loss	2,361	2,790
Regulatory amortization	0	0
Regulatory asset	2,371	2,801
Pension plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	100	245
Reclassification adjustments	6
Total other comprehensive income (loss)	(76)	(145)
Ending balance	24	100	245
Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	2,801	4,621
Reclassification adjustments	(247)	(297)
Total other comprehensive income (loss)	(430)	(1,820)
Ending balance	2,371	2,801	4,621
Pension plans | Net gain
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	82	128
Reclassification adjustments	6	(17)
Pension plans | Net gain | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	183	1,523
Reclassification adjustments	(246)	(296)
Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	(1)	(1)
Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	1	1
Net loss	(5)	(1)
Total AOCI	(4)	0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	(1)	3
Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	14	13
Net loss	(150)	(87)
Regulatory amortization	0	0
Regulatory liabilities	(136)	(74)
Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	0	8
Total other comprehensive income (loss)	(4)	(8)
Ending balance	(4)	0	8
Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(74)	51
Reclassification adjustments	2	(5)
Total other comprehensive income (loss)	(62)	(125)
Ending balance	(136)	(74)	51
Other postretirement benefit plans | Net gain
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	(3)	(11)
Other postretirement benefit plans | Net gain | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	64	120
Reclassification adjustments	1	(6)
Other postretirement benefit plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	1	1
Other postretirement benefit plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Alabama Power
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	10,713	9,810	8,955
Total other comprehensive income (loss)	4	6	4
Ending balance	11,687	10,713	9,810
Alabama Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Alabama Power | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	4	5
Net loss	675	804
Regulatory amortization	0	0
Regulatory asset	679	809
Alabama Power | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	809	1,286
Reclassification adjustments	(63)	(83)
Total other comprehensive income (loss)	(130)	(477)
Ending balance	679	809	1,286
Alabama Power | Pension plans | Net gain | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	67	394
Reclassification adjustments	(62)	(82)
Alabama Power | Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	(1)	(1)
Alabama Power | Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Alabama Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Alabama Power | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	4	3
Net loss	(25)	(65)
Regulatory amortization	0	0
Regulatory liabilities	(21)	(62)
Alabama Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(62)	(21)
Reclassification adjustments	0	0
Total other comprehensive income (loss)	41	(41)
Ending balance	(21)	(62)	(21)
Alabama Power | Other postretirement benefit plans | Net gain | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	(41)	41
Reclassification adjustments	0	0
Alabama Power | Other postretirement benefit plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Alabama Power | Other postretirement benefit plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Georgia Power
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	17,234	16,501	15,065
Total other comprehensive income (loss)	28	6	4
Ending balance	18,858	17,234	16,501
Georgia Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Georgia Power | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	7	8
Net loss	880	963
Regulatory amortization	0	0
Regulatory asset	887	971
Georgia Power | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	971	1,598
Reclassification adjustments	(75)	(100)
Total other comprehensive income (loss)	(84)	(627)
Ending balance	887	971	1,598
Georgia Power | Pension plans | Net gain | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	9	527
Reclassification adjustments	(74)	(99)
Georgia Power | Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	(1)	(1)
Georgia Power | Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Georgia Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Georgia Power | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	6	5
Net loss	(45)	(15)
Regulatory amortization	0	0
Regulatory liabilities	(39)	(10)
Georgia Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(10)	47
Reclassification adjustments	(2)	(2)
Total other comprehensive income (loss)	(29)	(57)
Ending balance	(39)	(10)	47
Georgia Power | Other postretirement benefit plans | Net gain | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	27	55
Reclassification adjustments	(2)	(3)
Georgia Power | Other postretirement benefit plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	1
Georgia Power | Other postretirement benefit plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Mississippi Power
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	1,867	1,742	1,652
Total other comprehensive income (loss)	0	1	1
Ending balance	1,931	1,867	1,742
Mississippi Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Mississippi Power | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	1	1
Net loss	122	145
Regulatory amortization	0	0
Regulatory asset	123	146
Mississippi Power | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	146	235
Reclassification adjustments	(11)	(15)
Total other comprehensive income (loss)	(23)	(89)
Ending balance	123	146	235
Mississippi Power | Pension plans | Net gain | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	12	74
Reclassification adjustments	(11)	(15)
Mississippi Power | Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Mississippi Power | Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Mississippi Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Total AOCI	0	0
Mississippi Power | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	1	1
Net loss	(10)	0
Regulatory amortization	0	0
Regulatory asset		1
Regulatory liabilities	(9)
Mississippi Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	1	5
Reclassification adjustments	0	0
Total other comprehensive income (loss)	(10)	(4)
Ending balance	(9)	1	5
Mississippi Power | Other postretirement benefit plans | Net gain | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	10	4
Reclassification adjustments	0	0
Mississippi Power | Other postretirement benefit plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Mississippi Power | Other postretirement benefit plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Southern Power
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	6,598	6,631	6,622
Total other comprehensive income (loss)	10	40	(42)
Ending balance	6,916	6,598	6,631
Southern Power | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(29)
Total other comprehensive income (loss)	20
Ending balance	(9)	(29)
Southern Power | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	0	0
Net loss	11	35
Total AOCI	11	35
Southern Power | Pension plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	35	60
Reclassification adjustments	(2)
Total other comprehensive income (loss)	(24)	(25)
Ending balance	11	35	60
Southern Power | Pension plans | Net gain
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	22	22
Reclassification adjustments	(2)	(3)
Southern Power | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	0	0
Net loss	0	2
Total AOCI	0	2
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Southern Power | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	2	3
Total other comprehensive income (loss)	(2)	(1)
Ending balance	0	2	3
Southern Power | Other postretirement benefit plans | Net gain
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	(2)	(1)
Southern Company Gas
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	9,916	9,767	9,506
Total other comprehensive income (loss)	7	46	(29)
Ending balance	10,397	9,916	9,767
Southern Company Gas | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	38
Total other comprehensive income (loss)	18
Ending balance	56	38
Southern Company Gas | Pension plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	(3)	(3)
Net loss	(72)	(42)
Total AOCI	(75)	(45)
Regulatory asset	190	210
Southern Company Gas | Pension plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	(9)	(11)
Net loss	66	38
Regulatory amortization	54	64
Regulatory asset	111	91
Southern Company Gas | Pension plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(45)	1
Reclassification adjustments	0
Total other comprehensive income (loss)	(30)	(46)
Ending balance	(75)	(45)	1
Southern Company Gas | Pension plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	91	205
Reclassification adjustments	(7)	(17)
Total other comprehensive income (loss)	20	(114)
Ending balance	111	91	205
Southern Company Gas | Pension plans | Net gain
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	30	47
Reclassification adjustments	0	1
Southern Company Gas | Pension plans | Net gain | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	(27)	97
Reclassification adjustments	1	(9)
Southern Company Gas | Pension plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	2	2
Southern Company Gas | Pension plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	(10)	(10)
Southern Company Gas | Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	0	1
Net loss	(2)	(6)
Total AOCI	(2)	(5)
Regulatory asset	32	40
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	3	(5)
Southern Company Gas | Other postretirement benefit plans | Regulatory Assets
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	1	1
Net loss	(64)	(51)
Regulatory amortization	5	16
Regulatory liabilities	(58)	(34)
Southern Company Gas | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(5)	0
Total other comprehensive income (loss)	3	(5)
Ending balance	(2)	(5)	0
Southern Company Gas | Other postretirement benefit plans | Pension and Other Postretirement Benefit Plans | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(34)	(23)
Reclassification adjustments	(11)	(9)
Total other comprehensive income (loss)	(24)	(11)
Ending balance	(58)	(34)	$ (23)
Southern Company Gas | Other postretirement benefit plans | Net gain
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	0	0
Southern Company Gas | Other postretirement benefit plans | Net gain | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Net gain	13	2
Reclassification adjustments	0	0
Southern Company Gas | Other postretirement benefit plans | Change in prior service costs | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	0	0
Southern Company Gas | Other postretirement benefit plans | Amortization of regulatory assets | Regulatory Assets
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassification adjustments	$ (11)	$ (9)