Related Party Transactions (Intercompany Income Taxes) (Details) - Affiliated Entity [Member] - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Duke Energy Carolinas [Member]
Related Party Transaction [Line Items]
Income taxes receivable	$ 32
Income tax payable		$ 44
Progress Energy [Member]
Related Party Transaction [Line Items]
Income taxes receivable	196	168
Duke Energy Progress [Member]
Related Party Transaction [Line Items]
Income taxes receivable	80
Income tax payable		21
Duke Energy Florida [Member]
Related Party Transaction [Line Items]
Income taxes receivable		44
Income tax payable	77
Duke Energy Ohio [Member]
Related Party Transaction [Line Items]
Income taxes receivable		22
Income tax payable	9
Duke Energy Indiana [Member]
Related Party Transaction [Line Items]
Income taxes receivable	22
Income tax payable		35
Piedmont Natural Gas [Member]
Related Party Transaction [Line Items]
Income taxes receivable	$ 11	$ 7