LEASES - Balance Sheet Amounts Recorded for Operating and Financing Leases (Details) $ in Millions	Dec. 31, 2019 USD ($)
Operating Leases
Operating lease ROU assets, net	$ 1,800
Operating lease obligations - current	229
Operating lease obligations - non-current	1,615
Total operating lease obligations	1,844
Finance Leases
Finance lease ROU assets, net	216
Finance lease obligations - current	21
Finance lease obligations - non-current	205
Total finance lease obligations	226
Alabama Power
Operating Leases
Operating lease ROU assets, net	132
Operating lease obligations - current	49
Operating lease obligations - non-current	107
Total operating lease obligations	156
Finance Leases
Finance lease ROU assets, net	4
Finance lease obligations - current	1
Finance lease obligations - non-current	3
Total finance lease obligations	4
Georgia Power
Operating Leases
Operating lease ROU assets, net	1,428
Operating lease obligations - current	144
Operating lease obligations - non-current	1,282
Total operating lease obligations	1,426
Finance Leases
Finance lease ROU assets, net	130
Finance lease obligations - current	11
Finance lease obligations - non-current	145
Total finance lease obligations	156
Mississippi Power
Operating Leases
Operating lease ROU assets, net	6
Operating lease obligations - current	2
Operating lease obligations - non-current	4
Total operating lease obligations	6
Finance Leases
Finance lease ROU assets, net	0
Finance lease obligations - current	0
Finance lease obligations - non-current	0
Total finance lease obligations	0
Southern Power
Operating Leases
Operating lease ROU assets, net	369
Operating lease obligations - current	22
Operating lease obligations - non-current	376
Total operating lease obligations	398
Finance Leases
Finance lease ROU assets, net	0
Finance lease obligations - current	0
Finance lease obligations - non-current	0
Total finance lease obligations	0
Southern Company Gas
Operating Leases
Operating lease ROU assets, net	93
Operating lease obligations - current	14
Operating lease obligations - non-current	78
Total operating lease obligations	92
Finance Leases
Finance lease ROU assets, net	0
Finance lease obligations - current	0
Finance lease obligations - non-current	0
Total finance lease obligations	$ 0