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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
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Investments    
Beginning balance $ 15 $ 4
Total pretax gains (losses) included in earnings   21
Purchases 33 24
Sales   (1)
Settlements (28) (37)
Total gains (losses) included on the Consolidated Balance Sheet as regulatory asset or liability 6 4
Ending balance (161) 15
Derivatives (net)    
Beginning balance 10 (1)
Total pretax gains (losses) included in earnings   21
Purchases 33 24
Sales   (1)
Settlements (28) (37)
Total Gains (losses) included on the Consolidated Balance Sheet as regulatory asset or liability 6 4
Ending balance (166) 10
Investments [Member]    
Investments    
Beginning balance 5 5
Ending balance 5 5
Duke Energy Ohio [Member]    
Derivatives (net)    
Beginning balance 3 (18)
Total pretax gains (losses) included in earnings   21
Purchases 5 5
Settlements (5) (5)
Total Gains (losses) included on the Consolidated Balance Sheet as regulatory asset or liability 2  
Ending balance 5 3
Duke Energy Indiana [Member]    
Derivatives (net)    
Beginning balance 7 14
Purchases 29 19
Settlements (24) (30)
Total Gains (losses) included on the Consolidated Balance Sheet as regulatory asset or liability 4 4
Ending balance 16 $ 7
Piedmont Natural Gas [Member]    
Investments    
Purchases (187)  
Derivatives (net)    
Purchases $ (187)