PROPERTY, PLANT, AND EQUIPMENT - Property, Plant and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Electric utilities:
Generation	$ 50,329	$ 52,324
Transmission	12,157	11,344
Distribution	19,846	18,746
General/other	4,650	4,446
Electric utilities' plant in service	86,982	86,860
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	13,518	12,409
Storage facilities	1,634	1,640
Other	1,192	1,128
Southern Company Gas plant in service	16,344	15,177
Other plant in service	1,788	1,669
Total plant in service	105,114	103,706
Alabama Power
Electric utilities:
Generation	15,329	16,533
Transmission	4,719	4,380
Distribution	7,798	7,389
General/other	2,177	2,100
Electric utilities' plant in service	30,023	30,402
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	0	0
Storage facilities	0	0
Other	0	0
Southern Company Gas plant in service	0	0
Other plant in service	0	0
Total plant in service	30,023	30,402
Georgia Power
Electric utilities:
Generation	18,341	19,145
Transmission	6,590	6,156
Distribution	11,024	10,389
General/other	2,182	1,985
Electric utilities' plant in service	38,137	37,675
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	0	0
Storage facilities	0	0
Other	0	0
Southern Company Gas plant in service	0	0
Other plant in service	0	0
Total plant in service	38,137	37,675
Mississippi Power
Electric utilities:
Generation	2,786	2,849
Transmission	808	769
Distribution	1,024	968
General/other	239	314
Electric utilities' plant in service	4,857	4,900
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	0	0
Storage facilities	0	0
Other	0	0
Southern Company Gas plant in service	0	0
Other plant in service	0	0
Total plant in service	4,857	4,900
Southern Power
Electric utilities:
Generation	13,241	13,246
Transmission	0	0
Distribution	0	0
General/other	29	25
Electric utilities' plant in service	13,270	13,271
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	0	0
Storage facilities	0	0
Other	0	0
Southern Company Gas plant in service	0	0
Other plant in service	0	0
Total plant in service	13,270	13,271
Southern Company Gas
Electric utilities:
Generation	0	0
Transmission	0	0
Distribution	0	0
General/other	0	0
Electric utilities' plant in service	0	0
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	13,518	12,409
Storage facilities	1,634	1,640
Other	1,192	1,128
Southern Company Gas plant in service	16,344	15,177
Other plant in service	0	0
Total plant in service	$ 16,344	$ 15,177