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Fair Value Measurements (Reconciliation of Assets and Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs) (Details) - USD ($) | 2 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Oct. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Fair Value Measurement Transfers Between Activity Levels |  | $ 0 | $ 0 | $ 0 |
Investments |  |  |  |  |
Beginning balance |  |  | 5,000,000 |  |
Total pretax realized and unrealized gains included in comprehensive income |  |  | 1,000,000 |  |
Sales |  |  | (6,000,000) |  |
Ending balance | $ 5,000,000 |  |  | 5,000,000 |
Derivatives (net) |  |  |  |  |
Beginning balance |  | (114,000,000) | (166,000,000) |  |
Purchases |  | 57,000,000 | 55,000,000 |  |
Settlements |  | (57,000,000) | (47,000,000) |  |
Total gains (losses) included on the Consolidated Balance Sheet |  | 1,000,000 | 44,000,000 |  |
Ending balance | (166,000,000) | (113,000,000) | (114,000,000) | (166,000,000) |
Investments and Derivatives, Net |  |  |  |  |
Beginning balance |  | (114,000,000) | (161,000,000) |  |
Total pretax realized or unrealized gains included in other comprehensive income |  |  | 1,000,000 |  |
Purchases |  |  | 55,000,000 |  |
Sales |  |  | (6,000,000) |  |
Settlements |  |  | (47,000,000) |  |
Total gains (losses) included on the Consolidated Balance Sheet |  |  | 44,000,000 |  |
Ending balance | (161,000,000) |  | (114,000,000) | (161,000,000) |
Duke Energy Carolinas [Member] |  |  |  |  |
Investments |  |  |  |  |
Beginning balance |  |  | 3,000,000 |  |
Total pretax realized and unrealized gains included in comprehensive income |  |  | 1,000,000 |  |
Sales |  |  | (4,000,000) |  |
Ending balance | 3,000,000 |  |  | 3,000,000 |
Duke Energy Ohio [Member] |  |  |  |  |
Derivatives (net) |  |  |  |  |
Beginning balance |  | 1,000,000 | 5,000,000 |  |
Purchases |  | 7,000,000 | 3,000,000 |  |
Settlements |  | (4,000,000) | (4,000,000) |  |
Total gains (losses) included on the Consolidated Balance Sheet |  | 2,000,000 | (3,000,000) |  |
Ending balance | 5,000,000 | 6,000,000 | 1,000,000 | 5,000,000 |
Duke Energy Indiana [Member] |  |  |  |  |
Derivatives (net) |  |  |  |  |
Beginning balance |  | 27,000,000 | 16,000,000 |  |
Purchases |  | 50,000,000 | 52,000,000 |  |
Settlements |  | (53,000,000) | (43,000,000) |  |
Total gains (losses) included on the Consolidated Balance Sheet |  | (2,000,000) | 2,000,000 |  |
Ending balance | 16,000,000 | 22,000,000 | 27,000,000 | 16,000,000 |
Piedmont Natural Gas [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Fair Value Measurement Transfers Between Activity Levels | 0 |  |  |  | $ 0
Derivatives (net) |  |  |  |  |
Beginning balance |  | (142,000,000) | (187,000,000) |  |
Total gains (losses) and settlements |  | 1,000,000 | 45,000,000 |  |
Ending balance | $ (187,000,000) | $ (141,000,000) | $ (142,000,000) | $ (187,000,000) |

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