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Fair Value Measurements (Quantitative Level 3 Fair Value Disclosures) (Details) $ in Millions | Jun. 30, 2019 USD ($) $ / MWh $ / MMBTU | Mar. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) $ / MWh $ / MMBTU | Jun. 30, 2018 USD ($) | Mar. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Jun. 30, 2017 USD ($)
--- | --- | --- | --- | --- | --- | --- | ---
Fair Value Measurement Inputs and Valuation Techniques |  |  |  |  |  |  |
Net derivative asset (liability) | $ (79) | $ (115) | $ (113) | $ (97) | $ (124) | $ (114) |
Duke Energy Ohio [Member] | Financial Transmission Rights [Member] | Valuation, Market Approach [Member] |  |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques |  |  |  |  |  |  |
Net derivative asset (liability) | $ 7 |  | $ 6 |  |  |  |
Duke Energy Ohio [Member] | Financial Transmission Rights [Member] | Minimum [Member] | Valuation, Market Approach [Member] |  |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques |  |  |  |  |  |  |
Input measurements (in usd per MWh and usd per MMBtu) | $ / MWh | 0.36 |  | 1.19 |  |  |  |
Duke Energy Ohio [Member] | Financial Transmission Rights [Member] | Maximum [Member] | Valuation, Market Approach [Member] |  |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques |  |  |  |  |  |  |
Input measurements (in usd per MWh and usd per MMBtu) | $ / MWh | 3.13 |  | 4.59 |  |  |  |
Duke Energy Indiana [Member] |  |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques |  |  |  |  |  |  |
Net derivative asset (liability) | $ 28 | 5 | $ 22 | 44 |  | 27 | $ 7
Duke Energy Indiana [Member] | Financial Transmission Rights [Member] | Valuation, Market Approach [Member] |  |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques |  |  |  |  |  |  |
Net derivative asset (liability) | $ 28 |  | $ 22 |  |  |  |
Duke Energy Indiana [Member] | Financial Transmission Rights [Member] | Minimum [Member] | Valuation, Market Approach [Member] |  |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques |  |  |  |  |  |  |
Input measurements (in usd per MWh and usd per MMBtu) | $ / MWh | (0.59) |  | (2.07) |  |  |  |
Duke Energy Indiana [Member] | Financial Transmission Rights [Member] | Maximum [Member] | Valuation, Market Approach [Member] |  |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques |  |  |  |  |  |  |
Input measurements (in usd per MWh and usd per MMBtu) | $ / MWh | 7.61 |  | 8.27 |  |  |  |
Piedmont Natural Gas [Member] |  |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques |  |  |  |  |  |  |
Net derivative asset (liability) | $ (114) | $ (121) | $ (141) | $ (150) | $ (132) | $ (142) |
Piedmont Natural Gas [Member] | Derivative Financial Instruments, Liabilities [Member] | Discounted Cash Flow [Member] |  |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques |  |  |  |  |  |  |
Net derivative asset (liability) | $ (114) |  | $ (141) |  |  |  |
Piedmont Natural Gas [Member] | Derivative Financial Instruments, Liabilities [Member] | Minimum [Member] | Discounted Cash Flow [Member] |  |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques |  |  |  |  |  |  |
Input measurements (in usd per MWh and usd per MMBtu) | $ / MMBTU | 1.96 |  | 1.87 |  |  |  |
Piedmont Natural Gas [Member] | Derivative Financial Instruments, Liabilities [Member] | Maximum [Member] | Discounted Cash Flow [Member] |  |  |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques |  |  |  |  |  |  |
Input measurements (in usd per MWh and usd per MMBtu) | $ / MMBTU | 3.21 |  | 2.95 |  |  |  |

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