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Fair Value Measurements (Quantitative Level 3 Fair Value Disclosure) (Details) $ in Millions | Dec. 31, 2020 USD ($) $ / MWh | Dec. 31, 2019 USD ($) $ / MWh $ / MMBTU | Dec. 31, 2018 USD ($)
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Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Net derivative asset (liability) | $ | $ (77) | $ (102) | $ (113)
Forward natural gas curves – price per MMBtu | Discounted cash flow |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Net derivative asset (liability) | $ | $ (84) |  |
Forward natural gas curves – price per MMBtu | Minimum | Discounted cash flow |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Input measurement (in usd per MWh and usd per MMBtu) | 14.68 |  |
Forward natural gas curves – price per MMBtu | Maximum | Discounted cash flow |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Input measurement (in usd per MWh and usd per MMBtu) | 151.84 |  |
Forward natural gas curves – price per MMBtu | Weighted Average | Discounted cash flow |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Input measurement (in usd per MWh and usd per MMBtu) | 28.84 |  |
Duke Energy Ohio | FTR price – per MWh | RTO auction pricing |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Net derivative asset (liability) | $ | $ 1 | $ 4 |
Duke Energy Ohio | FTR price – per MWh | Minimum | RTO auction pricing |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Input measurement (in usd per MWh and usd per MMBtu) | 0.25 | 0.59 |
Duke Energy Ohio | FTR price – per MWh | Maximum | RTO auction pricing |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Input measurement (in usd per MWh and usd per MMBtu) | 1.68 | 3.47 |
Duke Energy Ohio | FTR price – per MWh | Weighted Average | RTO auction pricing |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Input measurement (in usd per MWh and usd per MMBtu) | 0.79 | 2.07 |
Duke Energy Indiana |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Net derivative asset (liability) | $ | $ 6 | $ 11 | 22
Duke Energy Indiana | FTR price – per MWh | RTO auction pricing |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Net derivative asset (liability) | $ | $ 6 | $ 11 |
Duke Energy Indiana | FTR price – per MWh | Minimum | RTO auction pricing |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Input measurement (in usd per MWh and usd per MMBtu) | (2.40) | (0.66) |
Duke Energy Indiana | FTR price – per MWh | Maximum | RTO auction pricing |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Input measurement (in usd per MWh and usd per MMBtu) | 7.41 | 9.24 |
Duke Energy Indiana | FTR price – per MWh | Weighted Average | RTO auction pricing |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Input measurement (in usd per MWh and usd per MMBtu) | 1.05 | 1.15 |
Piedmont |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Net derivative asset (liability) | $ | $ 0 | $ (117) | $ (141)
Piedmont | Forward natural gas curves – price per MMBtu | Discounted cash flow |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Net derivative asset (liability) | $ |  | $ (117) |
Piedmont | Forward natural gas curves – price per MMBtu | Minimum | Discounted cash flow |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Input measurement (in usd per MWh and usd per MMBtu) | $ / MMBTU |  | 1.59 |
Piedmont | Forward natural gas curves – price per MMBtu | Maximum | Discounted cash flow |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Input measurement (in usd per MWh and usd per MMBtu) | $ / MMBTU |  | 2.46 |
Piedmont | Forward natural gas curves – price per MMBtu | Weighted Average | Discounted cash flow |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |
Input measurement (in usd per MWh and usd per MMBtu) | $ / MMBTU |  | 1.91 |

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