INCOME TAXES - Current and Deferred Income Tax Provisions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Federal —
Current	$ 50	$ 199	$ 156
Deferred	36	70	1,237
Total federal taxes	86	269	1,393
State —
Current	(25)	100	275
Deferred	206	24	130
Total state taxes	181	124	405
Income taxes	267	393	1,798
Alabama Power
Federal —
Current	104	198	61
Deferred	172	44	125
Total federal taxes	276	242	186
State —
Current	23	61	12
Deferred	73	34	72
Total state taxes	96	95	84
Income taxes	372	337	270
Georgia Power
Federal —
Current	311	365	264
Deferred	(449)	(224)	180
Total federal taxes	(138)	141	444
State —
Current	71	60	6
Deferred	(101)	(49)	22
Total state taxes	(30)	11	28
Income taxes	(168)	152	472
Mississippi Power
Federal —
Current	25	18	(6)
Deferred	(15)	(14)	26
Total federal taxes	10	4	20
State —
Current	0	0	(1)
Deferred	11	10	11
Total state taxes	11	10	10
Income taxes	21	14	30
Southern Power
Federal —
Current	(340)	(303)	(717)
Deferred	343	299	647
Total federal taxes	3	(4)	(70)
State —
Current	(16)	(4)	1
Deferred	0	11	13
Total state taxes	(16)	7	14
Income taxes	(13)	3	(56)
Southern Company Gas
Federal —
Current	85	82	(120)
Deferred	35	53	195
Total federal taxes	120	135	75
State —
Current	(68)	35	37
Deferred	223	3	18
Total state taxes	155	38	55
Income taxes	$ 275	$ 173	$ 130