Leases - Maturities of Lease Liabilities (Details) $ in Millions	Mar. 31, 2019 USD ($)
Operating leases:
2019 (remaining)	$ 253
2020	291
2021	274
2022	263
2023	198
Thereafter	1,637
Total	2,916
Less: Present value discount	925
Operating lease obligations, including held for sale	1,991
Finance leases:
2019 (remaining)	24
2020	32
2021	26
2022	22
2023	18
Thereafter	273
Total	395
Less: Present value discount	150
Finance lease obligations	245
ALABAMA POWER CO
Operating leases:
2019 (remaining)	46
2020	53
2021	52
2022	52
2023	3
Thereafter	1
Total	207
Less: Present value discount	13
Operating lease obligations	194
Finance leases:
2019 (remaining)	1
2020	1
2021	1
2022	1
2023	1
Thereafter	0
Total	5
Less: Present value discount	1
Finance lease obligations	4
GEORGIA POWER CO
Operating leases:
2019 (remaining)	182
2020	202
2021	197
2022	195
2023	196
Thereafter	984
Total	1,956
Less: Present value discount	413
Operating lease obligations	1,543
Finance leases:
2019 (remaining)	22
2020	28
2021	25
2022	25
2023	25
Thereafter	165
Total	290
Less: Present value discount	119
Finance lease obligations	171
MISSISSIPPI POWER CO
Operating leases:
2019 (remaining)	2
2020	2
2021	1
2022	1
2023	1
Thereafter	2
Total	9
Less: Present value discount	1
Operating lease obligations	8
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)	17
2020	22
2021	23
2022	23
2023	24
Thereafter	848
Total	957
Less: Present value discount	564
Operating lease obligations	393
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)	12
2020	16
2021	16
2022	12
2023	10
Thereafter	36
Total	102
Less: Present value discount	18
Operating lease obligations	84
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