LEASES - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Operating lease obligations	$ 1,754	$ 1,754	$ 1,852
Transfer of construction work in progress to lease receivables		$ 210
Communication towers
Lessee, Lease, Description [Line Items]
Lessee, renewal period		15 years
Maximum | Real estate
Lessee, Lease, Description [Line Items]
Remaining terms		24 years
Maximum | Land
Lessee, Lease, Description [Line Items]
Lessee, lease term		45 years
Maximum | Communication towers
Lessee, Lease, Description [Line Items]
Lessee, lease term		15 years
Maximum | Fuel cells
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	12 years	12 years
Alabama Power
Lessee, Lease, Description [Line Items]
Operating lease obligations	$ 121	$ 121	170
Alabama Power | Maximum | Electric generating units
Lessee, Lease, Description [Line Items]
Operating lease remaining lease term	17 years	17 years
Alabama Power | Minimum | Electric generating units
Lessee, Lease, Description [Line Items]
Operating lease remaining lease term	1 year	1 year
Georgia Power
Lessee, Lease, Description [Line Items]
Operating lease obligations	$ 1,155	$ 1,155	1,307
Variable lease, payment		41	39	$ 42
Georgia Power | Purchased power, affiliates
Lessee, Lease, Description [Line Items]
Variable lease, payment		20	20	20
Mississippi Power
Lessee, Lease, Description [Line Items]
Operating lease obligations	10	10	9
Transfer of construction work in progress to lease receivables		39	26
Sales-type lease, lease receivable	$ 39	$ 39	26
Mississippi Power | Maximum | Electric generating units
Lessee, Lease, Description [Line Items]
Lessor, sales-type lease, term of contract	17 years	17 years
Southern Power
Lessee, Lease, Description [Line Items]
Operating lease obligations	$ 525	$ 525	451
Lessor, sales-type lease, term of contract	20 years	20 years
Sales-type lease, lease receivable	$ 210	$ 210
Loss on sales-type leases	40	40	0	$ 0
Net investment in sales-type lease, current portion	12	12
Net investment in sales-type lease, long-term portion	$ 161	$ 161	0
Southern Power | Maximum | Electric generating units
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	25 years	25 years
Lessor, sales-type lease, term of contract	19 years	19 years
Southern Company Gas
Lessee, Lease, Description [Line Items]
Operating lease obligations	$ 70	$ 70	82
Southern Company Gas | Maximum
Lessee, Lease, Description [Line Items]
Lessor, remaining term		21 years
Affiliate | Georgia Power | Electric generating units
Lessee, Lease, Description [Line Items]
Operating lease obligations	$ 521	$ 521	$ 575
Traditional Electric Operating Companies | Maximum | Outdoor lighting
Lessee, Lease, Description [Line Items]
Lessor, lease term, operating lease	7 years	7 years