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Fair Value Measurements (Reconciliation of Assets and Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs) (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Derivatives (net)    
Beginning balance $ (166) $ 10
Settlements (9) (7)
Total amount included on the Condensed Consolidated Balance Sheet as regulatory assets or liabilities 40 (1)
Ending balance (135) 2
Investments and Derivatives, Net    
Beginning balance (161) 15
Sales   (1)
Settlements (9) (7)
Total amount included on the Condensed Consolidated Balance Sheet as regulatory assets or liabilities 40 (1)
Ending balance (130) 6
Investments [Member]    
Investments    
Beginning balance 5 5
Sales   (1)
Ending balance 5 4
Duke Energy Ohio [Member]    
Derivatives (net)    
Beginning balance 5 3
Settlements (1) (2)
Total amount included on the Condensed Consolidated Balance Sheet as regulatory assets or liabilities (3) (1)
Ending balance 1  
Duke Energy Indiana [Member]    
Derivatives (net)    
Beginning balance 16 7
Settlements (7) (5)
Ending balance 9 2
Piedmont Natural Gas [Member]    
Derivatives (net)    
Beginning balance (187) (149)
Total gains and settlements 42 23
Ending balance $ (145) $ (126)