Commitments and Contingencies (Schedule of Legal Reserves) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Reserves for legal matters	$ 83	$ 98
Duke Energy Carolinas [Member]
Loss Contingencies [Line Items]
Reserves for legal matters	23	23
Progress Energy [Member]
Loss Contingencies [Line Items]
Reserves for legal matters	56	59
Duke Energy Progress [Member]
Loss Contingencies [Line Items]
Reserves for legal matters	13	14
Duke Energy Florida [Member]
Loss Contingencies [Line Items]
Reserves for legal matters	28	28
Duke Energy Ohio [Member]
Loss Contingencies [Line Items]
Reserves for legal matters		4
Piedmont Natural Gas [Member]
Loss Contingencies [Line Items]
Reserves for legal matters	$ 2	$ 2