Fair Value Measurements (Quantitative Level 3 Fair Value Disclosure - Assets) (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($) $ / MWh	Dec. 31, 2016 USD ($) $ / MWh	Jun. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Net derivative asset (liability)	$ (93)	$ (166)	$ (91)	$ 23	$ 34	$ 10
Duke Energy Ohio [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Net derivative asset (liability)	2	5	3	3	5	3
Duke Energy Ohio [Member] | Financial Transmission Rights [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Net derivative asset (liability)	$ 2	$ 5
Duke Energy Ohio [Member] | Financial Transmission Rights [Member] | Minimum [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Input Price Per Unit | $ / MWh		0.77
Duke Energy Ohio [Member] | Financial Transmission Rights [Member] | Maximum [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Input Price Per Unit | $ / MWh	1.08	3.52
Duke Energy Indiana [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Net derivative asset (liability)	$ 28	$ 16	$ 51	$ 20	$ 29	$ 7
Duke Energy Indiana [Member] | Financial Transmission Rights [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Net derivative asset (liability)	$ 28	$ 16
Duke Energy Indiana [Member] | Financial Transmission Rights [Member] | Minimum [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Input Price Per Unit | $ / MWh	(0.82)	(0.83)
Duke Energy Indiana [Member] | Financial Transmission Rights [Member] | Maximum [Member] | Market Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Input Price Per Unit | $ / MWh	6.19	9.32