Related Party Transactions (Intercompany Income Taxes) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Piedmont Natural Gas [Member]
Related Party Transaction [Line Items]
Income taxes receivable	$ 99	$ 9
Affiliated Entity [Member] | Duke Energy Carolinas [Member]
Related Party Transaction [Line Items]
Income taxes receivable		1
Income tax payable	173
Affiliated Entity [Member] | Progress Energy [Member]
Related Party Transaction [Line Items]
Income taxes receivable	170
Income tax payable		37
Affiliated Entity [Member] | Duke Energy Progress [Member]
Related Party Transaction [Line Items]
Income tax payable	46	90
Affiliated Entity [Member] | Duke Energy Florida [Member]
Related Party Transaction [Line Items]
Income taxes receivable	120	37
Affiliated Entity [Member] | Duke Energy Ohio [Member]
Related Party Transaction [Line Items]
Income tax payable	18	1
Affiliated Entity [Member] | Duke Energy Indiana [Member]
Related Party Transaction [Line Items]
Income tax payable	104	3
Affiliated Entity [Member] | Piedmont Natural Gas [Member]
Related Party Transaction [Line Items]
Income taxes receivable	$ 89
Income tax payable		$ 38