Business Segments (Narrative) (Details) $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($) segment	Mar. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Loss on Sales of Other Assets and Other, net	$ 100	$ (11)
Operation, maintenance and other	1,464	1,468
Duke Energy Ohio [Member]
Segment Reporting Information [Line Items]
Loss on Sales of Other Assets and Other, net	106
Operation, maintenance and other	$ 131	$ 131
Number of Reportable Segments \| segment	2
Beckjord [Member]
Segment Reporting Information [Line Items]
Loss 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%

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

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Amount of gain (loss) on sale or disposal of assets, including but not limited to property plant and equipment, intangible assets and equity in securities of subsidiaries or equity method investee.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2443-110228

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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The amount of operating expenses for the period that are associated with the utility's normal revenue producing operation; including selling, general, and administrative expenses, costs incurred for routine plant repairs and maintenance, and operations.

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