INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Deferred tax liabilities —
Deferred income tax liabilities	$ 17,451	$ 16,781
Deferred tax assets —
Deferred income tax assets	8,914	8,874
Valuation allowance	(207)	(136)
Net deferred income tax assets	8,707	8,738
Net deferred income taxes liabilities	8,744	8,043
Accumulated deferred income taxes – assets	(118)	(132)
Accumulated deferred income taxes – liabilities	8,862	8,175
Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	9,300	8,950
Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	2,301	1,999
Federal effect of net state deferred tax assets/liabilities
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Deferred tax assets —
Deferred income tax assets	305	284
Leveraged lease basis differences
Deferred tax liabilities —
Deferred income tax liabilities	61	142
Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	820	739
Deferred tax assets —
Deferred income tax assets	1,035	1,511
Under recovered fuel and natural gas costs
Deferred tax liabilities —
Deferred income tax liabilities	315
Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities	18	80
Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	825	1,313
Remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	271	270
Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities	72	78
AROs
Deferred tax liabilities —
Deferred income tax liabilities	2,232	1,969
AROs
Deferred tax liabilities —
Deferred income tax liabilities	868	804
Other
Deferred tax liabilities —
Deferred income tax liabilities	368	437
State effect of federal deferred taxes
Deferred tax assets —
Deferred income tax assets	135	126
Other property basis differences
Deferred tax assets —
Deferred income tax assets	231	223
ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets	1,750	1,853
Long-term debt fair value adjustment
Deferred tax assets —
Deferred income tax assets	91	86
Other partnership basis difference
Deferred tax assets —
Deferred income tax assets	160	166
Other comprehensive losses
Deferred tax assets —
Deferred income tax assets	92	128
AROs
Deferred tax assets —
Deferred income tax assets	3,100	2,773
Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets	825	369
Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets	361	357
Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	268	338
Other
Deferred tax assets —
Deferred income tax assets	561	660
Alabama Power
Deferred tax liabilities —
Deferred income tax liabilities	5,737	5,416
Deferred tax assets —
Deferred income tax assets	2,164	2,143
Valuation allowance	0	0
Net deferred income tax assets	2,164	2,143
Net deferred income taxes liabilities	3,573	3,273
Accumulated deferred income taxes – assets	0	0
Accumulated deferred income taxes – liabilities	3,573	3,273
Alabama Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	2,541	2,453
Alabama Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	1,182	1,010
Alabama Power | Federal effect of net state deferred tax assets/liabilities
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Deferred tax assets —
Deferred income tax assets	165	151
Alabama Power | Leveraged lease basis differences
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Alabama Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	268	250
Deferred tax assets —
Deferred income tax assets	225	369
Alabama Power | Under recovered fuel and natural gas costs
Deferred tax liabilities —
Deferred income tax liabilities	47
Alabama Power | Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Alabama Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	205	348
Alabama Power | Remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	145	123
Alabama Power | Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities	10	12
Alabama Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	863	764
Alabama Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	329	328
Alabama Power | Other
Deferred tax liabilities —
Deferred income tax liabilities	147	128
Alabama Power | State effect of federal deferred taxes
Deferred tax assets —
Deferred income tax assets	135	126
Alabama Power | Other property basis differences
Deferred tax assets —
Deferred income tax assets	0	0
Alabama Power | ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets	12	12
Alabama Power | Long-term debt fair value adjustment
Deferred tax assets —
Deferred income tax assets	0	0
Alabama Power | Other partnership basis difference
Deferred tax assets —
Deferred income tax assets	0	0
Alabama Power | Other comprehensive losses
Deferred tax assets —
Deferred income tax assets	5	7
Alabama Power | AROs
Deferred tax assets —
Deferred income tax assets	1,192	1,092
Alabama Power | Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets	0	0
Alabama Power | Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets	0	0
Alabama Power | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	237	243
Alabama Power | Other
Deferred tax assets —
Deferred income tax assets	193	143
Georgia Power
Deferred tax liabilities —
Deferred income tax liabilities	6,965	6,680
Deferred tax assets —
Deferred income tax assets	4,019	3,443
Valuation allowance	(73)	(35)
Net deferred income tax assets	3,946	3,408
Net deferred income taxes liabilities	3,019	3,272
Accumulated deferred income taxes – assets	0	0
Accumulated deferred income taxes – liabilities	3,019	3,272
Georgia Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	3,340	3,228
Georgia Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	781	689
Georgia Power | Federal effect of net state deferred tax assets/liabilities
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Deferred tax assets —
Deferred income tax assets	41	59
Georgia Power | Leveraged lease basis differences
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Georgia Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	382	362
Deferred tax assets —
Deferred income tax assets	342	522
Georgia Power | Under recovered fuel and natural gas costs
Deferred tax liabilities —
Deferred income tax liabilities	109
Georgia Power | Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities	18	80
Georgia Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	256	438
Georgia Power | Remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	121	141
Georgia Power | Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities	62	66
Georgia Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	1,325	1,165
Georgia Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	494	429
Georgia Power | Other
Deferred tax liabilities —
Deferred income tax liabilities	77	82
Georgia Power | State effect of federal deferred taxes
Deferred tax assets —
Deferred income tax assets	0	0
Georgia Power | Other property basis differences
Deferred tax assets —
Deferred income tax assets	90	72
Georgia Power | ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets	704	539
Georgia Power | Long-term debt fair value adjustment
Deferred tax assets —
Deferred income tax assets	0	0
Georgia Power | Other partnership basis difference
Deferred tax assets —
Deferred income tax assets	0	0
Georgia Power | Other comprehensive losses
Deferred tax assets —
Deferred income tax assets	15	17
Georgia Power | AROs
Deferred tax assets —
Deferred income tax assets	1,819	1,594
Georgia Power | Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets	825	369
Georgia Power | Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets	11	9
Georgia Power | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	19	76
Georgia Power | Other
Deferred tax assets —
Deferred income tax assets	153	186
Mississippi Power
Deferred tax liabilities —
Deferred income tax liabilities	698	705
Deferred tax assets —
Deferred income tax assets	393	428
Valuation allowance	(41)	(41)
Net deferred income tax assets	352	387
Net deferred income taxes liabilities	346	318
Accumulated deferred income taxes – assets	(118)	(129)
Accumulated deferred income taxes – liabilities	464	447
Mississippi Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	330	319
Mississippi Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	169	148
Mississippi Power | Federal effect of net state deferred tax assets/liabilities
Deferred tax liabilities —
Deferred income tax liabilities	22	25
Deferred tax assets —
Deferred income tax assets	0	0
Mississippi Power | Leveraged lease basis differences
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Mississippi Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	41	39
Deferred tax assets —
Deferred income tax assets	57	80
Mississippi Power | Under recovered fuel and natural gas costs
Deferred tax liabilities —
Deferred income tax liabilities	15
Mississippi Power | Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Mississippi Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	38	62
Mississippi Power | Remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	5	6
Mississippi Power | Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Mississippi Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	44	40
Mississippi Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Mississippi Power | Other
Deferred tax liabilities —
Deferred income tax liabilities	34	66
Mississippi Power | State effect of federal deferred taxes
Deferred tax assets —
Deferred income tax assets	0	0
Mississippi Power | Other property basis differences
Deferred tax assets —
Deferred income tax assets	0	0
Mississippi Power | ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets	0	0
Mississippi Power | Long-term debt fair value adjustment
Deferred tax assets —
Deferred income tax assets	0	0
Mississippi Power | Other partnership basis difference
Deferred tax assets —
Deferred income tax assets	0	0
Mississippi Power | Other comprehensive losses
Deferred tax assets —
Deferred income tax assets	0	0
Mississippi Power | AROs
Deferred tax assets —
Deferred income tax assets	44	40
Mississippi Power | Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets	0	0
Mississippi Power | Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets	246	250
Mississippi Power | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	12	19
Mississippi Power | Other
Deferred tax assets —
Deferred income tax assets	34	39
Southern Power
Deferred tax liabilities —
Deferred income tax liabilities	1,446	1,413
Deferred tax assets —
Deferred income tax assets	1,258	1,587
Valuation allowance	(27)	(35)
Net deferred income tax assets	1,231	1,552
Net deferred income taxes liabilities	215
Net deferred income taxes assets		(139)
Accumulated deferred income taxes – assets	0	(262)
Accumulated deferred income taxes – liabilities	215	123
Southern Power | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	1,421	1,389
Southern Power | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | Federal effect of net state deferred tax assets/liabilities
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Deferred tax assets —
Deferred income tax assets	27	26
Southern Power | Leveraged lease basis differences
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	11	12
Deferred tax assets —
Deferred income tax assets	7	6
Southern Power | Under recovered fuel and natural gas costs
Deferred tax liabilities —
Deferred income tax liabilities	0
Southern Power | Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | Remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | AROs
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Power | Other
Deferred tax liabilities —
Deferred income tax liabilities	14	12
Southern Power | State effect of federal deferred taxes
Deferred tax assets —
Deferred income tax assets	0	0
Southern Power | Other property basis differences
Deferred tax assets —
Deferred income tax assets	121	134
Southern Power | ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets	827	1,110
Southern Power | Long-term debt fair value adjustment
Deferred tax assets —
Deferred income tax assets	0	0
Southern Power | Other partnership basis difference
Deferred tax assets —
Deferred income tax assets	160	166
Southern Power | Other comprehensive losses
Deferred tax assets —
Deferred income tax assets	11	25
Southern Power | AROs
Deferred tax assets —
Deferred income tax assets	0	0
Southern Power | Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets	0	0
Southern Power | Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets	52	68
Southern Power | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	0	0
Southern Power | Other
Deferred tax assets —
Deferred income tax assets	53	52
Southern Company Gas
Deferred tax liabilities —
Deferred income tax liabilities	1,874	1,693
Deferred tax assets —
Deferred income tax assets	328	432
Valuation allowance	(9)	(4)
Net deferred income tax assets	319	428
Net deferred income taxes liabilities	1,555	1,265
Accumulated deferred income taxes – assets	0	0
Accumulated deferred income taxes – liabilities	1,555	1,265
Southern Company Gas | Accelerated depreciation
Deferred tax liabilities —
Deferred income tax liabilities	1,428	1,349
Southern Company Gas | Property basis differences
Deferred tax liabilities —
Deferred income tax liabilities	148	135
Southern Company Gas | Federal effect of net state deferred tax assets/liabilities
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Deferred tax assets —
Deferred income tax assets	93	70
Southern Company Gas | Leveraged lease basis differences
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Company Gas | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	57	26
Deferred tax assets —
Deferred income tax assets	77	100
Southern Company Gas | Under recovered fuel and natural gas costs
Deferred tax liabilities —
Deferred income tax liabilities	144
Southern Company Gas | Storm damage reserves
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Company Gas | Employee benefit obligations
Deferred tax liabilities —
Deferred income tax liabilities	15	45
Southern Company Gas | Remaining book value of retired assets
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Company Gas | Premium on reacquired debt
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Company Gas | AROs
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Company Gas | AROs
Deferred tax liabilities —
Deferred income tax liabilities	0	0
Southern Company Gas | Other
Deferred tax liabilities —
Deferred income tax liabilities	82	138
Southern Company Gas | State effect of federal deferred taxes
Deferred tax assets —
Deferred income tax assets	0	0
Southern Company Gas | Other property basis differences
Deferred tax assets —
Deferred income tax assets	0	0
Southern Company Gas | ITC and PTC carryforward
Deferred tax assets —
Deferred income tax assets	0	0
Southern Company Gas | Long-term debt fair value adjustment
Deferred tax assets —
Deferred income tax assets	91	86
Southern Company Gas | Other partnership basis difference
Deferred tax assets —
Deferred income tax assets	0	0
Southern Company Gas | Other comprehensive losses
Deferred tax assets —
Deferred income tax assets	0	0
Southern Company Gas | AROs
Deferred tax assets —
Deferred income tax assets	0	0
Southern Company Gas | Estimated loss on plants under construction
Deferred tax assets —
Deferred income tax assets	0	0
Southern Company Gas | Other deferred state tax attributes
Deferred tax assets —
Deferred income tax assets	5	10
Southern Company Gas | Regulatory liability associated with the Tax Reform Legislation (not subject to normalization)
Deferred tax assets —
Deferred income tax assets	0	0
Southern Company Gas | Other
Deferred tax assets —
Deferred income tax assets	$ 62	$ 166