LEASES - Major Categories of Lease Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Lease obligations	$ 1,969	$ 2,083
Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	124	175
Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	1,291	1,452
Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	28	28
Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	526	451
Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	70	82
Electric generating units
Lessee, Lease, Description [Line Items]
Lease obligations	802	941
Electric generating units | Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	104	146
Electric generating units | Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	1,217	1,368
Electric generating units | Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Electric generating units | Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Electric generating units | Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Real estate/land
Lessee, Lease, Description [Line Items]
Lease obligations	876	815
Real estate/land | Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	3	4
Real estate/land | Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	49	53
Real estate/land | Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	2	2
Real estate/land | Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	526	451
Real estate/land | Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	45	61
Communication towers
Lessee, Lease, Description [Line Items]
Lease obligations	156	158
Communication towers | Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	2	2
Communication towers | Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	4	3
Communication towers | Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Communication towers | Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Communication towers | Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	24	20
Railcars
Lessee, Lease, Description [Line Items]
Lease obligations	32	42
Railcars | Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	10	16
Railcars | Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	20	23
Railcars | Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	2	3
Railcars | Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Railcars | Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Other
Lessee, Lease, Description [Line Items]
Lease obligations	103	127
Other | Alabama Power
Lessee, Lease, Description [Line Items]
Lease obligations	5	7
Other | Georgia Power
Lessee, Lease, Description [Line Items]
Lease obligations	1	5
Other | Mississippi Power
Lessee, Lease, Description [Line Items]
Lease obligations	24	23
Other | Southern Power
Lessee, Lease, Description [Line Items]
Lease obligations	0	0
Other | Southern Company Gas
Lessee, Lease, Description [Line Items]
Lease obligations	$ 1	$ 1