Related Party Transactions (Intercompany Income Taxes) (Details) - Affiliated Entity [Member] - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Duke Energy Carolinas [Member]
Related Party Transaction [Line Items]
Income tax payable	$ 9	$ 44
Progress Energy [Member]
Related Party Transaction [Line Items]
Income taxes receivable	183	168
Duke Energy Progress [Member]
Related Party Transaction [Line Items]
Income taxes receivable	13
Income tax payable		21
Duke Energy Florida [Member]
Related Party Transaction [Line Items]
Income taxes receivable	9	44
Duke Energy Ohio [Member]
Related Party Transaction [Line Items]
Income taxes receivable		22
Income tax payable	3
Duke Energy Indiana [Member]
Related Party Transaction [Line Items]
Income tax payable	18	35
Piedmont Natural Gas [Member]
Related Party Transaction [Line Items]
Income taxes receivable		$ 7
Income tax payable	$ 43