Derivatives and Hedging (Derivative Instruments with Credit-Risk Related Contingent Features and Cash Collateral) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Schedule of Information Regarding Derivative Instruments That Contain Credit-Risk Related Contingent Features
Aggregate fair value amounts of derivative instruments in a net liability position	$ 48	$ 59
Additional cash collateral or letters of credit in the event credit-risk-related contingent features were triggered	48	59
Duke Energy Carolinas [Member]
Schedule of Information Regarding Derivative Instruments That Contain Credit-Risk Related Contingent Features
Aggregate fair value amounts of derivative instruments in a net liability position	26	35
Additional cash collateral or letters of credit in the event credit-risk-related contingent features were triggered	26	35
Progress Energy [Member]
Schedule of Information Regarding Derivative Instruments That Contain Credit-Risk Related Contingent Features
Aggregate fair value amounts of derivative instruments in a net liability position	23	25
Additional cash collateral or letters of credit in the event credit-risk-related contingent features were triggered	23	25
Duke Energy Progress [Member]
Schedule of Information Regarding Derivative Instruments That Contain Credit-Risk Related Contingent Features
Aggregate fair value amounts of derivative instruments in a net liability position	22	15
Additional cash collateral or letters of credit in the event credit-risk-related contingent features were triggered	$ 22	15
Duke Energy Florida [Member]
Schedule of Information Regarding Derivative Instruments That Contain Credit-Risk Related Contingent Features
Aggregate fair value amounts of derivative instruments in a net liability position		10
Additional cash collateral or letters of credit in the event credit-risk-related contingent features were triggered		$ 10