Derivatives - Narrative (Details) BTU in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) BTU
Derivative [Line Items]
Maximum Potential Collateral Requirements Arising from Credit Risk Related Contingent Features | $	$ 54
Southern Company [Member]
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	5
Georgia Power [Member]
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	4
Southern Power [Member]
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints	1