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Acquisitions and Dispositions (Pro Forma Information) (Details) - Piedmont Natural Gas [Member] - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Business Acquisition [Line Items]    
Revenues $ 23,504 $ 23,570
Net income attributable to Duke Energy Corporation $ 2,442 $ 2,877