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Business Segments (Narrative) (Details) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 USD ($) | Jun. 30, 2017 USD ($) | Jun. 30, 2018 USD ($) segment | Jun. 30, 2017 USD ($)
Segment Reporting Information [Line Items] |  |  |  |
Gains (Losses) on Sales of Other Assets and Other, net | $ (3) | $ (7) | $ 97 | $ (18)
Operation, maintenance and other | 1,544 | 1,441 | 3,008 | 2,909
Duke Energy Ohio [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Gains (Losses) on Sales of Other Assets and Other, net |  |  | 106 |
Operation, maintenance and other | $ 130 | $ 132 | $ 261 | $ 263
Number of Reportable Segments | segment |  |  | 2 |
Beckjord [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Gains (Losses) on Sales of Other Assets and Other, net |  |  | $ (106) |
Operation, maintenance and other |  |  | $ 1 |
National Methanol Company [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Equity Method Investment, Ownership Percentage | 17.50% |  | 17.50% |

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