Joint Ownership of Generating and Transmission Facilities Joint Ownership of Generating and Transmission Facilities (Narrative) (Details) - Crystal River Nuclear Station (Unit 3) [Member] $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Seminole Electric Cooperative [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	1.70%
Florida Municipal Joint Owners [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	6.52%
Joint Owner Settlement	$ 55
Duke Energy Florida [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	98.30%