Contingencies and Regulatory Matters - Recovery Balance of Each Regulatory Clause - Gulf Power (Details) - Gulf Power [Member] - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Other regulatory liabilities, current [Member]
Loss Contingencies [Line Items]
Fuel Cost Recovery	$ 5	$ 15
Environmental Cost Recovery	40	13
Under recovered regulatory clause revenues [Member]
Loss Contingencies [Line Items]
Purchased Power Capacity Recovery	4	0
Energy Conservation Cost Recovery	$ 3	$ 4