Commitments and Contingencies (Schedule of Reserves) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Loss Contingencies [Line Items]
Reserves for legal matters	$ 178	$ 323
Duke Energy Carolinas [Member]
Loss Contingencies [Line Items]
Reserves for legal matters	12	72
Progress Energy [Member]
Loss Contingencies [Line Items]
Reserves for legal matters	74	93
Duke Energy Progress [Member]
Loss Contingencies [Line Items]
Reserves for legal matters	17	37
Duke Energy Florida [Member]
Loss Contingencies [Line Items]
Reserves for legal matters	36	$ 36
Duke Energy Ohio [Member]
Loss Contingencies [Line Items]
Reserves for legal matters	$ 81