Contingencies and Regulatory Matters - Recovery Balance of Each Regulatory Clause - Gulf Power (Details) - Gulf Power [Member] - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Under recovered regulatory clause revenues [Member]
Loss Contingencies [Line Items]
Fuel Cost Recovery – Under	$ 2	$ 40
Environmental Cost Recovery – Under	0	10
Energy Conservation Cost Recovery – Under	0	3
Other regulatory liabilities, current [Member]
Loss Contingencies [Line Items]
Purchased Power Capacity Recovery – Over	3	0
Environmental Cost Recovery - Over	5	0
Energy Conservation Cost Recovery – Over	$ 3	$ 0