Derivatives and Hedging (Interest Rate Risk) (Details) (Interest Rate Contracts [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivative [Line Items]
Notional amount	$ 791	$ 832
Cash Flow Hedging [Member]
Derivative [Line Items]
Notional amount	764	798
Duke Energy Ohio [Member]
Derivative [Line Items]
Notional amount	27	27
Duke Energy Ohio [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Notional amount
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional amount	27	34
Not Designated as Hedging Instrument [Member] | Duke Energy Ohio [Member]
Derivative [Line Items]
Notional amount	27	27
Variable Interest Entity, Primary Beneficiary [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Notional amount	$ 552	$ 584