Summary of Significant Accounting Policies (Unbilled Revenues)(Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Organization And Basis Of Presentation [Line Items]
Unbilled receivables	$ 944	$ 831
Duke Energy Carolinas [Member]
Organization And Basis Of Presentation [Line Items]
Unbilled receivables	342	313
Progress Energy [Member]
Organization And Basis Of Presentation [Line Items]
Unbilled receivables	228	161
Duke Energy Progress [Member]
Organization And Basis Of Presentation [Line Items]
Unbilled receivables	143	102
Duke Energy Florida [Member]
Organization And Basis Of Presentation [Line Items]
Unbilled receivables	85	59
Duke Energy Ohio [Member]
Organization And Basis Of Presentation [Line Items]
Unbilled receivables	4	2
Duke Energy Indiana [Member]
Organization And Basis Of Presentation [Line Items]
Unbilled receivables	21	32
Piedmont Natural Gas [Member]
Organization And Basis Of Presentation [Line Items]
Unbilled receivables	86	77
Cinergy Receivables [Member] | Duke Energy Ohio [Member]
Organization And Basis Of Presentation [Line Items]
Unbilled receivables	104	97
Cinergy Receivables [Member] | Duke Energy Indiana [Member]
Organization And Basis Of Presentation [Line Items]
Unbilled receivables	$ 132	$ 123