Regulatory Matters (Refunds) (Details) (Duke Energy Florida [Member], USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended			3 Months Ended	12 Months Ended		3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended			3 Months Ended	12 Months Ended			3 Months Ended	12 Months Ended
	Mar. 31, 2014 Florida Public Service Commission Settlement Agreement 2012 [Member]	Dec. 31, 2016 Florida Public Service Commission Settlement Agreement 2012 [Member] Scenario Forecast [Member]	Dec. 31, 2015 Florida Public Service Commission Settlement Agreement 2012 [Member] Scenario Forecast [Member]	Dec. 31, 2014 Florida Public Service Commission Settlement Agreement 2012 [Member] Scenario Forecast [Member]	Mar. 31, 2014 Retirement Decision Credits [Member]	Dec. 31, 2016 Retirement Decision Credits [Member] Scenario Forecast [Member]	Dec. 31, 2015 Retirement Decision Credits [Member] Scenario Forecast [Member]	Mar. 31, 2014 Neil Settlement [Member]	Dec. 31, 2014 Neil Settlement [Member] Scenario Forecast [Member]	Mar. 31, 2014 Total Customer Refunds [Member]	Dec. 31, 2016 Total Customer Refunds [Member] Scenario Forecast [Member]	Dec. 31, 2015 Total Customer Refunds [Member] Scenario Forecast [Member]	Dec. 31, 2014 Total Customer Refunds [Member] Scenario Forecast [Member]	Mar. 31, 2014 Accelerated Regulatory Asset Recovery [Member]	Dec. 31, 2016 Accelerated Regulatory Asset Recovery [Member] Scenario Forecast [Member]	Dec. 31, 2015 Accelerated Regulatory Asset Recovery [Member] Scenario Forecast [Member]	Dec. 31, 2014 Accelerated Regulatory Asset Recovery [Member] Scenario Forecast [Member]	Mar. 31, 2014 Net Customer Refunds [Member]	Dec. 31, 2016 Net Customer Refunds [Member] Scenario Forecast [Member]	Dec. 31, 2015 Net Customer Refunds [Member] Scenario Forecast [Member]	Dec. 31, 2014 Net Customer Refunds [Member] Scenario Forecast [Member]
Regulatory Assets Liabilities [Line Items]
Customer refunds to date	$ 164							$ 367		$ 531				$ (8)				$ 523
2014				104					123				227				(29)				198
2015			10				40					50				(37)				13
2016		10				60					70				(56)				14
Total Customer Refunds To Be Paid	$ 288				$ 100			$ 490		$ 878				$ (130)				$ 748