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Commitments and Contingencies (Schedule of Legal Reserves) (Details) - USD ($) $ in Millions | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Loss Contingencies [Line Items] |  |
Reserves for legal matters | $ 63 | $ 88
Duke Energy Carolinas [Member] |  |
Loss Contingencies [Line Items] |  |
Reserves for legal matters | 11 | 30
Progress Energy [Member] |  |
Loss Contingencies [Line Items] |  |
Reserves for legal matters | 50 | 55
Duke Energy Progress [Member] |  |
Loss Contingencies [Line Items] |  |
Reserves for legal matters | 11 | 13
Duke Energy Florida [Member] |  |
Loss Contingencies [Line Items] |  |
Reserves for legal matters | 23 | 24
Piedmont Natural Gas [Member] |  |
Loss Contingencies [Line Items] |  |
Reserves for legal matters | $ 1 | $ 2

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- Definition Amount of loss contingency liability. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349 + Details
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