Variable Interest Entities (Fair Value Assumptions)(Details) - Cinergy Receivables [Member] - Variable Interest Entity, Not Primary Beneficiary [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Duke Energy Ohio [Member]
Variable Interest Entity [Line Items]
Anticipated credit loss ratio	0.50%	0.50%
Discount rate	2.10%	1.50%
Receivable turnover rate	13.50%	13.30%
Duke Energy Indiana [Member]
Variable Interest Entity [Line Items]
Anticipated credit loss ratio	0.30%	0.30%
Discount rate	2.10%	1.50%
Receivable turnover rate	10.70%	10.60%