Fair Value Measurements (Quantitative Level 3 Fair Value Disclosure - Assets) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) $ / MWh	Dec. 31, 2016 USD ($) $ / MWh	Dec. 31, 2015 USD ($)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Net Derivative Asset (Liability)	$ (114)	$ (166)	$ 10
Duke Energy Ohio [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Net Derivative Asset (Liability)	1	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)	$ 1	$ 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	0.07	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	1.41	3.52
Duke Energy Indiana [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Net Derivative Asset (Liability)	$ 27	$ 16	$ 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)	$ 27	$ 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	(0.77)	(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	7.44	9.32