Variable Interest Entities (Fair Value Assumptions) (Details) - Variable Interest Entity, Not Primary Beneficiary [Member] - Cinergy Receivables [Member]	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Duke Energy Ohio [Member]
Variable Interest Entities [Line Items]
Anticipated credit loss ratio	0.50%	0.50%
Discount rate	2.90%	2.10%
Receivable turnover rate	13.60%	13.50%
Duke Energy Indiana [Member]
Variable Interest Entities [Line Items]
Anticipated credit loss ratio	0.30%	0.30%
Discount rate	2.90%	2.10%
Receivable turnover rate	10.90%	10.70%