Business Segments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Revenue, Net	$ 5,484	$ 5,589	$ 11,106	$ 11,654
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	510	600	1,201	1,373
Duke Energy Ohio [Member]
Segment Reporting Information [Line Items]
Revenue, Net	428	405	944	991
Commercial Portfolio [Member]
Segment Reporting Information [Line Items]
Revenue, Net	112	75	227	148
Commercial Portfolio [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue, Net	112	75	227	148
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	14	(30)	41	(23)
Commercial Portfolio [Member] \| Duke Energy Ohio [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue, Net				14
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent				9
International Energy [Member]
Segment Reporting Information [Line Items]
Revenue, Net	270	287	516	560
International Energy [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue, Net	270	287	516	560
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	$ (102)	$ 52	$ 21	$ 88
National Methanol Company [Member] \| International Energy [Member]
Segment Reporting Information [Line Items]
Equity Method Investment, Ownership Percentage	25.00%		25.00%

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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.13)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 4: http://www.xbrl.org/2003/role/presentationRef
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Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
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-Section S99
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