Derivatives - Narrative (Details) BTU in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($) BTU
Derivative [Line Items]
Collateral already posted, aggregate fair value | $	$ 111
Maximum potential collateral requirements arising from credit risk related contingent features | $	$ 22
Parent Company And Georgia Power [Member]
Derivative [Line Items]
Expected volume of natural gas subject to option to sell back excess gas due to operational constraints | BTU	5
Southern Company [Member]
Derivative [Line Items]
Interest rate cash flow hedge gain (loss) to be reclassified during next 12 months | $	$ (21)
Parent Company and Southern Power [Member]
Derivative [Line Items]
Foreign currency cash flow hedge gain (loss) to be reclassified during next 12 months | $	$ (12)
Energy-related, Natural Gas [Member] | Georgia Power [Member]
Derivative [Line Items]
Net quantity Purchase of Derivatives not designated as hedges | BTU	148
Energy-related, Natural Gas [Member] | Southern Power [Member]
Derivative [Line Items]
Net quantity Purchase of Derivatives not designated as hedges | BTU	9
Energy-related, Natural Gas [Member] | Southern Company [Member]
Derivative [Line Items]
Net quantity Purchase of Derivatives not designated as hedges | BTU	540