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Business Segments (Narrative) (Details) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 USD ($) | Sep. 30, 2017 USD ($) | Sep. 30, 2018 USD ($) segment | Sep. 30, 2017 USD ($)
Segment Reporting Information [Line Items] |  |  |  |
Pretax loss on disposal | $ (10) | $ (6) | $ 87 | $ (24)
Operation, maintenance and other | 1,584 | 1,476 | 4,592 | 4,385
Duke Energy Ohio [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Pretax loss on disposal |  | (1) | 106 | (1)
Operation, maintenance and other | $ 76 | $ 125 | $ 337 | $ 388
Number of reportable segments | segment |  |  | 2 |
Beckjord [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Pretax loss on disposal |  |  | $ 106 |
Operation, maintenance and other |  |  | $ 1 |
National Methanol Company [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Ownership percentage | 17.50% |  | 17.50% |

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