Variable Interest Entities (Sales and Cash Flows)(Details) - Cinergy Receivables [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Duke Energy Ohio [Member]
Variable Interest Entities [Line Items]
Receivables sold	$ 449	$ 477	$ 1,518	$ 1,705
Loss recognized on sale	2	3	7	9
Cash proceeds from receivables sold	461	494	1,568	1,761
Collection fees received	0		1	1
Return received on retained interests	0		2	3
Duke Energy Indiana [Member]
Variable Interest Entities [Line Items]
Receivables sold	679	739	2,032	2,173
Loss recognized on sale	3	3	8	8
Cash proceeds from receivables sold	692	759	2,074	2,233
Collection fees received	0		1	1
Return received on retained interests	$ 1	$ 2	$ 4	$ 5