Property, Plant, and Equipment - Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Electric utilities:
Generation	$ 52,324	$ 51,279
Transmission	11,344	11,562
Distribution	18,746	19,239
General/other	4,446	4,402
Electric utilities' plant in service	86,860	86,482
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	12,409	13,079
Storage facilities	1,640	1,599
Other	1,128	1,155
Southern Company Gas plant in service	15,177	15,833
Other plant in service	1,669	1,227
Total plant in service	103,706	103,542
Alabama Power
Electric utilities:
Generation	16,533	14,213
Transmission	4,380	4,119
Distribution	7,389	7,034
General/other	2,100	1,960
Electric utilities' plant in service	30,402	27,326
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	30,402	27,326
Georgia Power
Electric utilities:
Generation	19,145	17,038
Transmission	6,156	5,947
Distribution	10,389	9,978
General/other	1,985	1,898
Electric utilities' plant in service	37,675	34,861
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	37,675	34,861
Mississippi Power
Electric utilities:
Generation	2,849	2,801
Transmission	769	737
Distribution	968	946
General/other	314	289
Electric utilities' plant in service	4,900	4,773
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	4,900	4,773
Southern Power
Electric utilities:
Generation	13,246	13,737
Transmission	0	0
Distribution	0	0
General/other	25	18
Electric utilities' plant in service	13,271	13,755
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	13,271	13,755
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	12,409	13,079
Storage facilities	1,640	1,599
Other	1,128	1,155
Southern Company Gas plant in service	15,177	15,833
Other plant in service	0	0
Total plant in service	$ 15,177	$ 15,833
Natural gas | Southern Power
Southern Company Gas:
Useful life	45 years
Biomass | Southern Power
Southern Company Gas:
Useful life	40 years
Solar | Southern Power
Southern Company Gas:
Useful life	35 years
Wind | Southern Power
Southern Company Gas:
Useful life	30 years