Related Party Transactions (Intercompany Income Taxes) (Details) - Affiliated Entity [Member] - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Duke Energy Carolinas [Member]
Related Party Transaction [Line Items]
Accrued Income Taxes, Current	$ 44
Income taxes receivable, current		$ 1
Progress Energy [Member]
Related Party Transaction [Line Items]
Accrued Income Taxes, Current		37
Income taxes receivable, current	168
Duke Energy Progress [Member]
Related Party Transaction [Line Items]
Accrued Income Taxes, Current	21	90
Duke Energy Florida [Member]
Related Party Transaction [Line Items]
Income taxes receivable, current	44	37
Duke Energy Ohio [Member]
Related Party Transaction [Line Items]
Accrued Income Taxes, Current		1
Income taxes receivable, current	22
Duke Energy Indiana [Member]
Related Party Transaction [Line Items]
Accrued Income Taxes, Current	35	3
Piedmont Natural Gas [Member]
Related Party Transaction [Line Items]
Accrued Income Taxes, Current		$ 38
Income taxes receivable, current	$ 7