Regulatory Matters (Refunds) (Details) (Duke Energy Florida [Member], USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Florida Public Service Commission Settlement Agreement 2012 [Member]
Regulatory Assets Liabilities [Line Items]
Customer refunds to date	$ 97
Total Customer Refunds To Be Paid	288
Florida Public Service Commission Settlement Agreement 2012 [Member] | Scenario Forecast [Member]
Regulatory Assets Liabilities [Line Items]
2013	32
2014				139
2015			10
2016		10
Retirement Decision Credits [Member]
Regulatory Assets Liabilities [Line Items]
2015			40
2016		60
Total Customer Refunds To Be Paid	100
Neil Settlement [Member]
Regulatory Assets Liabilities [Line Items]
Customer refunds to date	245
Total Customer Refunds To Be Paid	490
Neil Settlement [Member] | Scenario Forecast [Member]
Regulatory Assets Liabilities [Line Items]
2013	81
2014				164
Total Customer Refunds [Member]
Regulatory Assets Liabilities [Line Items]
Customer refunds to date	342
Total Customer Refunds To Be Paid	878
Total Customer Refunds [Member] | Scenario Forecast [Member]
Regulatory Assets Liabilities [Line Items]
2013	113
2014				303
2015			50
2016		70
Accelerated Regulatory Asset Recovery [Member]
Regulatory Assets Liabilities [Line Items]
Total Customer Refunds To Be Paid	(135)
Accelerated Regulatory Asset Recovery [Member] | Scenario Forecast [Member]
Regulatory Assets Liabilities [Line Items]
2014				(38)
2015			(38)
2016		(59)
Net Customer Refunds [Member]
Regulatory Assets Liabilities [Line Items]
Customer refunds to date	342
Total Customer Refunds To Be Paid	743
Net Customer Refunds [Member] | Scenario Forecast [Member]
Regulatory Assets Liabilities [Line Items]
2013	113
2014				265
2015			12
2016		$ 11