Joint Ownership of Generating and Transmission Facilities (Narrative) (Details) - Duke Energy Florida [Member] $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Ownership Percentage of Generating Facility	100.00%
Seminole Electric Cooperative [Member] | Crystal River Nuclear Station (Unit 3) [Member]
Jointly Owned Utility Plant Interests [Line Items]
Joint owner ownership percentage	1.70%
Florida Municipal Joint Owners [Member] | Crystal River Nuclear Station (Unit 3) [Member]
Jointly Owned Utility Plant Interests [Line Items]
Joint owner ownership percentage	6.52%
Joint Owner Settlement	$ 55