Summary of Significant Accounting Policies - Property, Plant, and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Generation	$ 41,648	$ 37,892
Transmission	10,544	9,884
Distribution	17,670	17,123
General	4,377	4,198
Plant acquisition adjustment	123	123
Utility plant in service	74,362	69,220
Information technology equipment and software	222	244
Communications equipment	418	439
Other	116	110
Other plant in service	756	793
Total plant in service	75,118	70,013
Alabama Power [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Generation	12,820	11,670
Transmission	3,773	3,579
Distribution	6,432	6,196
General	1,713	1,623
Plant acquisition adjustment	12	12
Total plant in service	24,750	23,080
Georgia Power [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Generation	15,386	15,201
Transmission	5,355	5,086
Distribution	9,151	8,913
General	1,921	1,855
Plant acquisition adjustment	28	28
Total plant in service	31,841	31,083
Gulf Power [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Generation	2,974	2,638
Transmission	691	516
Distribution	1,196	1,157
General	182	182
Plant acquisition adjustment	2	2
Total plant in service	5,045	4,495
Mississippi Power [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Generation	2,723	2,293
Transmission	688	665
Distribution	891	854
General	503	485
Plant acquisition adjustment	81	81
Total plant in service	$ 4,886	$ 4,378