Leases - Maturities of Lease Liabilities (Details) $ in Millions	Sep. 30, 2019 USD ($)
Operating leases:
2019 (remaining)	$ 45
2020	284
2021	269
2022	259
2023	202
Thereafter	1,662
Total	2,721
Less: Present value discount	886
Operating lease obligations, including held for sale	1,835
Finance leases:
2019 (remaining)	9
2020	31
2021	24
2022	21
2023	17
Thereafter	259
Total	361
Less: Present value discount	133
Finance lease obligations	228
ALABAMA POWER CO
Operating leases:
2019 (remaining)	4
2020	54
2021	53
2022	52
2023	4
Thereafter	2
Total	169
Less: Present value discount	11
Operating lease obligations	158
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)	23
2020	205
2021	198
2022	196
2023	197
Thereafter	991
Total	1,810
Less: Present value discount	380
Operating lease obligations	1,430
Finance leases:
2019 (remaining)	4
2020	28
2021	24
2022	24
2023	25
Thereafter	161
Total	266
Less: Present value discount	109
Finance lease obligations	157
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
Finance lease obligations	0
SOUTHERN POWER CO
Operating leases:
2019 (remaining)	8
2020	22
2021	23
2022	23
2023	24
Thereafter	847
Total	947
Less: Present value discount	552
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
Finance lease obligations	0
SOUTHERN Co GAS
Operating leases:
2019 (remaining)	4
2020	17
2021	17
2022	13
2023	11
Thereafter	49
Total	111
Less: Present value discount	20
Operating lease obligations	91
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