Leases - Balance Sheet Amounts Recorded for Operating and Financing Leases (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Operating Leases
Operating lease ROU assets, net, including held for sale	$ 1,823
Operating lease ROU assets, net	1,818
Operating lease obligations - current, including held for sale	229
Operating lease obligations - current	229
Operating lease obligations - non current, including held for sale	1,606
Operating lease obligations - non current	1,601
Total operating lease obligations, including held for sale	1,835
Finance Leases
Finance lease ROU assets, net	220
Finance lease obligations - current	21
Finance lease obligations - noncurrent	207
Total finance lease obligations	228
ALABAMA POWER CO
Operating Leases
Operating lease ROU assets, net	143
Operating lease obligations - current	49
Operating lease obligations - non current	109
Total operating lease obligations	158
Finance Leases
Finance lease ROU assets, net	4
Finance lease obligations - current	1
Finance lease obligations - noncurrent	4
Total finance lease obligations	5
GEORGIA POWER CO
Operating Leases
Operating lease ROU assets, net	1,461
Operating lease obligations - current	143	$ 0
Operating lease obligations - non current	1,287
Total operating lease obligations	1,430
Finance Leases
Finance lease ROU assets, net	134
Finance lease obligations - current	12
Finance lease obligations - noncurrent	145
Total finance lease obligations	157
MISSISSIPPI POWER CO
Operating Leases
Operating lease ROU assets, net	7
Operating lease obligations - current	2
Operating lease obligations - non current	5
Total operating lease obligations	7
Finance Leases
Finance lease ROU assets, net	0
Finance lease obligations - current	0
Finance lease obligations - noncurrent	0
Total finance lease obligations	0
SOUTHERN POWER CO
Operating Leases
Operating lease ROU assets, net	368
Operating lease obligations - current	22
Operating lease obligations - non current	373
Total operating lease obligations	395
Finance Leases
Finance lease ROU assets, net	0
Finance lease obligations - current	0
Finance lease obligations - noncurrent	0
Total finance lease obligations	0
SOUTHERN Co GAS
Operating Leases
Operating lease ROU assets, net	92
Operating lease obligations - current	14
Operating lease obligations - non current	77
Total operating lease obligations	91
Finance Leases
Finance lease ROU assets, net	0
Finance lease obligations - current	0
Finance lease obligations - noncurrent	0
Total finance lease obligations	$ 0