LEASES - Lease Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Lease cost
Operating lease cost	$ 313	$ 309	$ 310
Finance lease cost:
Amortization of ROU assets	21	26	28
Interest on lease obligations	11	11	12
Total finance lease cost	32	37	40
Short-term lease costs	48	39	48
Variable lease cost	96	91	105
Sublease income	1	0	0
Total lease cost	490	476	503
Assets Subject to Power Purchase Agreement
Lease cost
Operating lease cost	165	161	149
Alabama Power
Lease cost
Operating lease cost	58	55	54
Finance lease cost:
Amortization of ROU assets	1	1	1
Interest on lease obligations	0	0	0
Total finance lease cost	1	1	1
Short-term lease costs	15	11	19
Variable lease cost	4	4	6
Sublease income	0	(1)	(1)
Total lease cost	78	70	79
Alabama Power | Assets Subject to Power Purchase Agreement
Lease cost
Operating lease cost	47	43	41
Georgia Power
Lease cost
Operating lease cost	208	212	206
Finance lease cost:
Amortization of ROU assets	11	15	15
Interest on lease obligations	16	16	18
Total finance lease cost	27	31	33
Short-term lease costs	24	26	22
Variable lease cost	83	76	85
Sublease income	0	0	0
Total lease cost	342	345	346
Georgia Power | Assets Subject to Power Purchase Agreement
Lease cost
Operating lease cost	184	184	174
Mississippi Power
Lease cost
Operating lease cost	2	3	3
Finance lease cost:
Amortization of ROU assets	1	0	0
Interest on lease obligations	1	0	0
Total finance lease cost	2	0	0
Short-term lease costs	0	0	0
Variable lease cost	0	0	0
Sublease income	0	0	0
Total lease cost	4	3	3
Southern Power
Lease cost
Operating lease cost	33	29	28
Finance lease cost:
Amortization of ROU assets	0	0	0
Interest on lease obligations	0	0	0
Total finance lease cost	0	0	0
Short-term lease costs	0	0	0
Variable lease cost	5	7	7
Sublease income	0	0	0
Total lease cost	38	36	35
Southern Company Gas
Lease cost
Operating lease cost	19	19	18
Finance lease cost:
Amortization of ROU assets	0	0	0
Interest on lease obligations	0	0	0
Total finance lease cost	0	0	0
Short-term lease costs	0	0	0
Variable lease cost	0	0	0
Sublease income	0	0	0
Total lease cost	$ 19	$ 19	$ 18