Introduction - Narrative (Details)			3 Months Ended
	Apr. 30, 2017 USD ($)	Apr. 01, 2017 USD ($)	Mar. 31, 2017 USD ($) kWh	Apr. 04, 2017 USD ($)	Mar. 31, 2016 USD ($)
Gulf Power [Member]
Related Party Transaction [Line Items]
Number of agreements for renewable generation			$ 40,000,000
Recovery period for natural disaster reserve costs			60 days
Cumulative costs limit under PSC order			$ 100,000,000
Southern Company Gas [Member] | Southern Power [Member]
Related Party Transaction [Line Items]
Related party transactions			23,000,000
Southern Natural Gas Company, LLC [Member] | Southern Company Gas [Member]
Related Party Transaction [Line Items]
Related party transactions			9,000,000
Southern Natural Gas Company, LLC [Member] | Alabama Power [Member]
Related Party Transaction [Line Items]
Related party transactions			1,000,000
Southern Natural Gas Company, LLC [Member] | Georgia Power [Member]
Related Party Transaction [Line Items]
Related party transactions			26,000,000
Southern Natural Gas Company, LLC [Member] | Southern Power [Member]
Related Party Transaction [Line Items]
Related party transactions			6,000,000
Subsequent Event [Member] | Georgia Power [Member]
Related Party Transaction [Line Items]
Property damage reserve, percentage of balance		0.75
Subsequent Event [Member] | Gulf Power [Member]
Related Party Transaction [Line Items]
Psc approved annual property damage reserve accrual		$ 3,500,000
Number of agreements for renewable generation				$ 0
Increase (decrease) in recoverable property damage costs	$ 31,000,000
Maximum [Member] | Gulf Power [Member]
Related Party Transaction [Line Items]
Customer surcharge storm recovery costs			$ 4.00
Customer surcharge storm recovery capacity | kWh			1,000
Wholesale Gas Services [Member] | Southern Company Gas [Member]
Related Party Transaction [Line Items]
Inventory valuation reserves			$ 0
Predecessor [Member] | Wholesale Gas Services [Member] | Southern Company Gas [Member]
Related Party Transaction [Line Items]
Inventory valuation reserves					$ 3,000,000