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

Amount of loss contingency liability.

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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant