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Related Party Transactions (Narrative) (Details) - Duke Energy Ohio [Member] - USD ($)
$ in Millions
Dec. 31, 2015
Apr. 01, 2015
Dec. 31, 2014
Related Party Transaction [Line Items]      
Intercompany loan payable $ 103   $ 491
DECAM [Member]      
Related Party Transaction [Line Items]      
Intercompany loan payable   $ 294 $ 459