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Fair Value Measurements (Quantitative Level 3 Fair Value Disclosure) (Details)
$ in Millions
6 Months Ended 12 Months Ended
Jun. 30, 2016
USD ($)
$ / MWh
Dec. 31, 2015
USD ($)
$ / MWh
Mar. 31, 2016
USD ($)
Jun. 30, 2015
USD ($)
Mar. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]            
Net derivative asset (liability) | $ $ 34 $ 10 $ 2 $ 23   $ (1)
Financial Transmission Rights [Member] | RTO Auction Pricing [Member]            
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]            
Net derivative asset (liability) | $ $ 34 $ 10        
Financial Transmission Rights [Member] | Minimum [Member] | RTO Auction Pricing [Member]            
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]            
Fair Value Inputs Price Per Financial Transmission Rights | $ / MWh (1.64) (0.74)        
Financial Transmission Rights [Member] | Maximum [Member] | RTO Auction Pricing [Member]            
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]            
Fair Value Inputs Price Per Financial Transmission Rights | $ / MWh 8.64 7.29        
Duke Energy Ohio [Member]            
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]            
Net derivative asset (liability) | $ $ 5 $ 3   5 $ 7 (18)
Duke Energy Ohio [Member] | Financial Transmission Rights [Member] | RTO Auction Pricing [Member]            
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]            
Net derivative asset (liability) | $ $ 5 $ 3        
Duke Energy Ohio [Member] | Financial Transmission Rights [Member] | Minimum [Member] | RTO Auction Pricing [Member]            
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]            
Fair Value Inputs Price Per Financial Transmission Rights | $ / MWh 0.36 0.67        
Duke Energy Ohio [Member] | Financial Transmission Rights [Member] | Maximum [Member] | RTO Auction Pricing [Member]            
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]            
Fair Value Inputs Price Per Financial Transmission Rights | $ / MWh 2.47 2.53        
Duke Energy Indiana [Member]            
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]            
Net derivative asset (liability) | $ $ 29 $ 7 $ 2 $ 17 $ 3 $ 14
Duke Energy Indiana [Member] | Financial Transmission Rights [Member] | RTO Auction Pricing [Member]            
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]            
Net derivative asset (liability) | $ $ 29 $ 7        
Duke Energy Indiana [Member] | Financial Transmission Rights [Member] | Minimum [Member] | RTO Auction Pricing [Member]            
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]            
Fair Value Inputs Price Per Financial Transmission Rights | $ / MWh (1.64) (0.74)        
Duke Energy Indiana [Member] | Financial Transmission Rights [Member] | Maximum [Member] | RTO Auction Pricing [Member]            
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]            
Fair Value Inputs Price Per Financial Transmission Rights | $ / MWh 8.64 7.29