Commitments and Contingencies (Schedule of Legal Reserves) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Legal Reserves Details [Line Items]
Reserves for legal matters	$ 88	$ 98
Duke Energy Carolinas [Member]
Legal Reserves Details [Line Items]
Reserves for legal matters	30	23
Progress Energy [Member]
Legal Reserves Details [Line Items]
Reserves for legal matters	55	59
Duke Energy Progress [Member]
Legal Reserves Details [Line Items]
Reserves for legal matters	13	14
Duke Energy Florida [Member]
Legal Reserves Details [Line Items]
Reserves for legal matters	24	28
Duke Energy Ohio [Member]
Legal Reserves Details [Line Items]
Reserves for legal matters		4
Piedmont Natural Gas [Member]
Legal Reserves Details [Line Items]
Reserves for legal matters	$ 2	$ 2