Variable Interest Entities (Sales and Cash Flows) (Details) - Variable Interest Entity, Not Primary Beneficiary [Member] - Cinergy Receivables [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Duke Energy Ohio [Member]
Variable Interest Entities [Line Items]
Receivables sold	$ 450	$ 438	$ 1,478	$ 1,392
Loss recognized on sale	4	2	10	7
Cash proceeds from receivables sold	449	434	1,499	1,421
Collection fees received		1	1	1
Return received on retained interests	2		5	2
Duke Energy Indiana [Member]
Variable Interest Entities [Line Items]
Receivables sold	754	720	2,140	2,047
Loss recognized on sale	5	3	12	9
Cash proceeds from receivables sold	743	713	2,140	2,064
Collection fees received			1	1
Return received on retained interests	$ 3	$ 2	$ 7	$ 5