Contingencies and Regulatory Matters Cost Recovery Clause (Details) (Gulf Power [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Under Recovered Regulatory Clause Revenues [Member]
Loss Contingencies [Line Items]
Under Recovered Fuel Cost	$ 35.7	$ 21.0
Under Recovered Purchased Power Capacity Costs	0	2.8
Under Recovered Environmental Cost	17.1	14.4
Under Recovered Energy Conservation Costs	6.3	7.0
Other regulatory liabilities current [Member]
Loss Contingencies [Line Items]
Over Recovered Purchased Power Capacity Costs	$ 5.5	$ 0