FAIR VALUE MEASUREMENTS - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Assets:
Derivative asset	$ 213	$ 281
Liabilities:
Derivative liability	125	64
Weather derivative premium		6
Collateral already posted, aggregate fair value		28
Recurring
Assets:
Cash equivalents	1,174	584
Other investments	44	33
Total	4,023	3,759
Liabilities:
Contingent consideration	14	17
Other	13
Total	181	637
Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	1,160	575
Other investments	9	9
Total	2,174	1,974
Liabilities:
Contingent consideration	0	0
Other	0
Total	10	389
Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	14	9
Other investments	35	24
Total	1,699	1,677
Liabilities:
Contingent consideration	0	0
Other	13
Total	157	227
Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Other investments	0	0
Total	0	32
Liabilities:
Contingent consideration	14	17
Other	0
Total	14	21
Recurring \| Fair Value Measured at Net Asset Value Per Share (NAV)
Assets:
Total	150	76
Alabama Power
Assets:
Derivative asset	50	5
Liabilities:
Derivative liability	6	0
Alabama Power \| Recurring
Assets:
Cash equivalents	853	320
Other investments	35	24
Total	2,267	1,512
Alabama Power \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	839	311
Other investments	0	0
Total	1,482	959
Alabama Power \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	14	9
Other investments	35	24
Total	635	477
Alabama Power \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Other investments	0	0
Total	0	0
Alabama Power \| Recurring \| Fair Value Measured at Net Asset Value Per Share (NAV)
Assets:
Total	150	76
Georgia Power
Assets:
Derivative asset	67	3
Liabilities:
Derivative liability	0	1
Georgia Power \| Recurring
Assets:
Total	1,292	1,160
Georgia Power \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total	336	340
Georgia Power \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Total	956	820
Georgia Power \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Total	0	0
Mississippi Power
Assets:
Derivative asset	52	2
Liabilities:
Derivative liability	1	2
Mississippi Power \| Recurring
Assets:
Cash equivalents	40	21
Total	96	30
Mississippi Power \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	40	21
Total	40	21
Mississippi Power \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0	0
Total	56	9
Mississippi Power \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Total	0	0
Southern Power
Assets:
Derivative asset	4	89
Liabilities:
Derivative liability	16	26
Southern Power \| Recurring
Assets:
Total		89
Liabilities:
Contingent consideration	14	17
Other	13
Total	43	43
Southern Power \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total		0
Liabilities:
Contingent consideration	0	0
Other	0
Total	0	0
Southern Power \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Total		89
Liabilities:
Contingent consideration	0	0
Other	13
Total	29	26
Southern Power \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Total		0
Liabilities:
Contingent consideration	14	17
Other	0
Total	14	17
Southern Company Gas
Assets:
Derivative asset	27	162
Liabilities:
Derivative liability	16	35
Collateral already posted, aggregate fair value	3	28
Southern Company Gas \| Recurring
Assets:
Cash equivalents		1
Total	61	696
Liabilities:
Total	27
Southern Company Gas \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents		1
Total	26	402
Liabilities:
Total	10
Southern Company Gas \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents		0
Total	35	262
Liabilities:
Total	17
Southern Company Gas \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents		0
Total	0	32
Liabilities:
Total	0
Energy-related derivatives \| Recurring
Assets:
Derivative asset	219	704
Liabilities:
Derivative liability	46	597
Energy-related derivatives \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	24	401
Liabilities:
Derivative liability	10	389
Energy-related derivatives \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	195	271
Liabilities:
Derivative liability	36	204
Energy-related derivatives \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0	32
Liabilities:
Derivative liability	0	4
Energy-related derivatives \| Alabama Power \| Recurring
Assets:
Derivative asset	55	12
Liabilities:
Derivative liability	11	7
Energy-related derivatives \| Alabama Power \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Energy-related derivatives \| Alabama Power \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	55	12
Liabilities:
Derivative liability	11	7
Energy-related derivatives \| Alabama Power \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Energy-related derivatives \| Georgia Power \| Recurring
Assets:
Derivative asset	75	15
Liabilities:
Derivative liability	8	13
Energy-related derivatives \| Georgia Power \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Energy-related derivatives \| Georgia Power \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	75	15
Liabilities:
Derivative liability	8	13
Energy-related derivatives \| Georgia Power \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Energy-related derivatives \| Mississippi Power \| Recurring
Assets:
Derivative asset	56	9
Liabilities:
Derivative liability	5	9
Energy-related derivatives \| Mississippi Power \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Energy-related derivatives \| Mississippi Power \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	56	9
Liabilities:
Derivative liability	5	9
Energy-related derivatives \| Mississippi Power \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Energy-related derivatives \| Southern Power \| Recurring
Assets:
Derivative asset	4	2
Liabilities:
Derivative liability		3
Energy-related derivatives \| Southern Power \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability		0
Energy-related derivatives \| Southern Power \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	4	2
Liabilities:
Derivative liability		3
Energy-related derivatives \| Southern Power \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability		0
Energy-related derivatives \| Southern Company Gas \| Recurring
Assets:
Derivative asset	29	666
Liabilities:
Derivative liability	22	565
Energy-related derivatives \| Southern Company Gas \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	24	401
Liabilities:
Derivative liability	10	389
Energy-related derivatives \| Southern Company Gas \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	5	233
Liabilities:
Derivative liability	12	172
Energy-related derivatives \| Southern Company Gas \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0	32
Liabilities:
Derivative liability	0	4
Interest rate derivatives \| Recurring
Assets:
Derivative asset	19	20
Liabilities:
Derivative liability	29
Interest rate derivatives \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0
Interest rate derivatives \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	19	20
Liabilities:
Derivative liability	29
Interest rate derivatives \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0
Interest rate derivatives \| Southern Company Gas \| Recurring
Assets:
Derivative asset	6
Liabilities:
Derivative liability	5
Interest rate derivatives \| Southern Company Gas \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset	0
Liabilities:
Derivative liability	0
Interest rate derivatives \| Southern Company Gas \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	6
Liabilities:
Derivative liability	5
Interest rate derivatives \| Southern Company Gas \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	0
Liabilities:
Derivative liability	0
Foreign currency derivatives \| Recurring
Assets:
Derivative asset		87
Liabilities:
Derivative liability	79	23
Foreign currency derivatives \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset		0
Liabilities:
Derivative liability	0	0
Foreign currency derivatives \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset		87
Liabilities:
Derivative liability	79	23
Foreign currency derivatives \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset		0
Liabilities:
Derivative liability	0	0
Foreign currency derivatives \| Southern Power \| Recurring
Assets:
Derivative asset		87
Liabilities:
Derivative liability	16	23
Foreign currency derivatives \| Southern Power \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative asset		0
Liabilities:
Derivative liability	0	0
Foreign currency derivatives \| Southern Power \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset		87
Liabilities:
Derivative liability	16	23
Foreign currency derivatives \| Southern Power \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset		0
Liabilities:
Derivative liability	0	0
Domestic equity \| Recurring
Assets:
Nuclear decommissioning trusts	1,016	1,013
Domestic equity \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	791	862
Domestic equity \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	225	151
Domestic equity \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Domestic equity \| Alabama Power \| Recurring
Assets:
Nuclear decommissioning trusts	684	684
Domestic equity \| Alabama Power \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	468	543
Domestic equity \| Alabama Power \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	216	141
Domestic equity \| Alabama Power \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Domestic equity \| Georgia Power \| Recurring
Assets:
Nuclear decommissioning trusts	324	320
Domestic equity \| Georgia Power \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	323	319
Domestic equity \| Georgia Power \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	1	1
Domestic equity \| Georgia Power \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Domestic equity \| Southern Company Gas \| Recurring
Assets:
Non-qualified deferred compensation trusts	8	9
Domestic equity \| Southern Company Gas \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	0	0
Domestic equity \| Southern Company Gas \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	8	9
Domestic equity \| Southern Company Gas \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	0	0
Foreign equity \| Recurring
Assets:
Nuclear decommissioning trusts	353	338
Foreign equity \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	165	85
Foreign equity \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	188	253
Foreign equity \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Foreign equity \| Alabama Power \| Recurring
Assets:
Nuclear decommissioning trusts	165	158
Foreign equity \| Alabama Power \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	165	85
Foreign equity \| Alabama Power \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	0	73
Foreign equity \| Alabama Power \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Foreign equity \| Georgia Power \| Recurring
Assets:
Nuclear decommissioning trusts	185	177
Foreign equity \| Georgia Power \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
Foreign equity \| Georgia Power \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	185	177
Foreign equity \| Georgia Power \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
Foreign equity \| Southern Company Gas \| Recurring
Assets:
Non-qualified deferred compensation trusts	3	3
Foreign equity \| Southern Company Gas \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Non-qualified deferred compensation trusts	0	0
Foreign equity \| Southern Company Gas \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Non-qualified deferred compensation trusts	3	3
Foreign equity \| Southern Company Gas \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Non-qualified deferred compensation trusts	0	0
U.S. Treasury and government agency securities \| Recurring
Assets:
Nuclear decommissioning trusts	314	284
U.S. Treasury and government agency securities \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
U.S. Treasury and government agency securities \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	314	284
U.S. Treasury and government agency securities \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
U.S. Treasury and government agency securities \| Alabama Power \| Recurring
Assets:
Nuclear decommissioning trusts	21	21
U.S. Treasury and government agency securities \| Alabama Power \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0
U.S. Treasury and government agency securities \| Alabama Power \| Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Nuclear decommissioning trusts	21	21
U.S. Treasury and government agency securities \| Alabama Power \| Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Nuclear decommissioning trusts	0	0
U.S. Treasury and government agency securities \| Georgia Power \| Recurring
Assets:
Nuclear decommissioning trusts	293	263
U.S. Treasury and government agency securities \| Georgia Power \| Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Nuclear decommissioning trusts	0	0

FAIR VALUE MEASUREMENTS - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($)
$ in Millions

Dec. 31, 2021

Dec. 31, 2020

Assets:

Derivative asset

$ 213

$ 281

Liabilities:

Derivative liability

125

Weather derivative premium

Collateral already posted, aggregate fair value