Contingencies and Regulatory Matters - Recovery Balance of Each Regulatory Clause - Gulf Power (Details) - Gulf Power [Member] - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Other regulatory liabilities, current [Member]
Loss Contingencies [Line Items]
Fuel Cost Recovery	$ 20	$ 18
Purchased Power Capacity Recovery - Over	3	0
Environmental Cost Recovery	5	0
Energy Conservation Cost Recovery	0	4
Under recovered regulatory clause revenues [Member]
Loss Contingencies [Line Items]
Purchased Power Capacity Recovery - Under	0	1
Environmental Cost Recovery	0	19
Energy Conservation Costs - Under	$ 2	$ 0