Contingencies and Regulatory Matters - Cost Recovery Clause (Details) (Under Recovered Regulatory Clause Revenues [Member], Gulf Power [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Under Recovered Regulatory Clause Revenues [Member] | Gulf Power [Member]
Loss Contingencies [Line Items]
Under Recovered Fuel Cost	$ 32	$ 40
Under Recovered Purchased Power Capacity Costs	3	0
Under Recovered Environmental Cost	12	10
Under Recovered Energy Conservation Costs	$ 1	$ 3