Derivatives - Narrative (Details) - Jun. 30, 2015 BTU in Millions, $ in Millions	USD ($) BTU
Derivatives (Textual) [Abstract]
Maximum Potential Collateral Requirements Arising from Credit Risk Related Contingent Features	$ 49
Southern Company [Member]
Derivatives (Textual) [Abstract]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | BTU	5
Alabama Power [Member]
Derivatives (Textual) [Abstract]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | BTU	1
Maximum Potential Collateral Requirements Arising from Credit Risk Related Contingent Features	$ 49
Georgia Power [Member]
Derivatives (Textual) [Abstract]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | BTU	3
Maximum Potential Collateral Requirements Arising from Credit Risk Related Contingent Features	$ 49
Southern Power [Member]
Derivatives (Textual) [Abstract]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | BTU	1
Maximum Potential Collateral Requirements Arising from Credit Risk Related Contingent Features	$ 49
Gulf Power [Member]
Derivatives (Textual) [Abstract]
Maximum Potential Collateral Requirements Arising from Credit Risk Related Contingent Features	49
Mississippi Power [Member]
Derivatives (Textual) [Abstract]
Maximum Potential Collateral Requirements Arising from Credit Risk Related Contingent Features	$ 49