Leases - Maturities of Lease Liabilities (Details) $ in Millions	Jun. 30, 2019 USD ($)
Operating leases:
2019 (remaining)	$ 178
2020	295
2021	279
2022	268
2023	204
Thereafter	1,661
Total	2,885
Less: Present value discount	911
Operating lease obligations, including held for sale	1,974
Finance leases:
2019 (remaining)	16
2020	33
2021	27
2022	23
2023	18
Thereafter	266
Total	383
Less: Present value discount	139
Finance lease obligations	244
ALABAMA POWER CO
Operating leases:
2019 (remaining)	33
2020	53
2021	52
2022	52
2023	4
Thereafter	2
Total	196
Less: Present value discount	11
Operating lease obligations	185
Finance leases:
2019 (remaining)	0
2020	1
2021	1
2022	1
2023	1
Thereafter	1
Total	5
Less: Present value discount	0
Finance lease obligations	5
GEORGIA POWER CO
Operating leases:
2019 (remaining)	129
2020	203
2021	198
2022	196
2023	197
Thereafter	990
Total	1,913
Less: Present value discount	396
Operating lease obligations	1,517
Finance leases:
2019 (remaining)	16
2020	28
2021	25
2022	25
2023	25
Thereafter	165
Total	284
Less: Present value discount	115
Finance lease obligations	169
MISSISSIPPI POWER CO
Operating leases:
2019 (remaining)	1
2020	2
2021	1
2022	1
2023	1
Thereafter	2
Total	8
Less: Present value discount	1
Operating lease obligations	7
Finance leases:
2019 (remaining)	0
2020	0
2021	0
2022	0
2023	0
Thereafter	0
Total	0
Less: Present value discount	0
Finance lease obligations	0
SOUTHERN POWER CO
Operating leases:
2019 (remaining)	13
2020	22
2021	23
2022	23
2023	24
Thereafter	849
Total	954
Less: Present value discount	559
Operating lease obligations	395
Finance leases:
2019 (remaining)	0
2020	0
2021	0
2022	0
2023	0
Thereafter	0
Total	0
Less: Present value discount	0
Finance lease obligations	0
SOUTHERN Co GAS
Operating leases:
2019 (remaining)	9
2020	17
2021	16
2022	13
2023	11
Thereafter	49
Total	115
Less: Present value discount	21
Operating lease obligations	94
Finance leases:
2019 (remaining)	0
2020	0
2021	0
2022	0
2023	0
Thereafter	0
Total	0
Less: Present value discount	0
Finance lease obligations	$ 0