LEASES - Maturities of Lease Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Operating leases:
2022	$ 307
2023	238
2024	195
2025	174
2026	154
Thereafter	1,575
Total	2,643
Less: Present value discount	889
Operating lease obligations	1,754	$ 1,852
Finance leases:
2022	25
2023	22
2024	19
2025	16
2026	16
Thereafter	231
Total	329
Less: Present value discount	114
Finance lease obligations	215	231
Alabama Power
Operating leases:
2022	59
2023	9
2024	7
2025	6
2026	5
Thereafter	69
Total	155
Less: Present value discount	34
Operating lease obligations	121	170
Finance leases:
2022	2
2023	1
2024	1
2025	0
2026	0
Thereafter	0
Total	4
Less: Present value discount	0
Finance lease obligations	4	5
Georgia Power
Operating leases:
2022	205
2023	201
2024	164
2025	136
2026	133
Thereafter	566
Total	1,405
Less: Present value discount	250
Operating lease obligations	1,155	1,307
Finance leases:
2022	25
2023	25
2024	25
2025	25
2026	26
Thereafter	83
Total	209
Less: Present value discount	73
Finance lease obligations	136	145
Mississippi Power
Operating leases:
2022	4
2023	2
2024	1
2025	1
2026	1
Thereafter	2
Total	11
Less: Present value discount	1
Operating lease obligations	10	9
Finance leases:
2022	2
2023	2
2024	2
2025	2
2026	1
Thereafter	13
Total	22
Less: Present value discount	4
Finance lease obligations	18	19
Southern Power
Operating leases:
2022	37
2023	29
2024	29
2025	29
2026	30
Thereafter	995
Total	1,149
Less: Present value discount	624
Operating lease obligations	525	451
Finance leases:
2022	0
2023	0
2024	0
2025	0
2026	0
Thereafter	0
Total	0
Less: Present value discount	0
Finance lease obligations	0	0
Southern Company Gas
Operating leases:
2022	14
2023	11
2024	11
2025	11
2026	8
Thereafter	31
Total	86
Less: Present value discount	16
Operating lease obligations	70	82
Finance leases:
2022	0
2023	0
2024	0
2025	0
2026	0
Thereafter	0
Total	0
Less: Present value discount	0
Finance lease obligations	$ 0	$ 0