Summary of Significant Accounting Policies (Excise Taxes)(Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2016	Dec. 31, 2015	Oct. 31, 2015
Organization And Basis Of Presentation [Line Items]
Excise taxes	$ 376	$ 362		$ 396
Duke Energy Carolinas [Member]
Organization And Basis Of Presentation [Line Items]
Excise taxes	36	31		31
Progress Energy [Member]
Organization And Basis Of Presentation [Line Items]
Excise taxes	220	213		229
Duke Energy Progress [Member]
Organization And Basis Of Presentation [Line Items]
Excise taxes	19	18		16
Duke Energy Florida [Member]
Organization And Basis Of Presentation [Line Items]
Excise taxes	201	195		213
Duke Energy Ohio [Member]
Organization And Basis Of Presentation [Line Items]
Excise taxes	98	100		102
Duke Energy Indiana [Member]
Organization And Basis Of Presentation [Line Items]
Excise taxes	20	$ 17		$ 34
Piedmont Natural Gas [Member]
Organization And Basis Of Presentation [Line Items]
Excise taxes	$ 2		$ 2		$ 2