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Related Party Transactions (Narrative) (Details) - Duke Energy Ohio [Member] - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Apr. 01, 2015
Dec. 31, 2014
Related Party Transaction [Line Items]          
Intercompany loan payable   $ 5     $ 491
DECAM [Member]          
Related Party Transaction [Line Items]          
Intercompany loan payable       $ 294 $ 459
MarkTo Market Of Commodity Contracts And Sales Of Power [Member] | DECAM [Member]          
Related Party Transaction [Line Items]          
Related party transaction, expenses from transactions with related party $ 27 $ 3 $ 81