Fair Value Measurements (Additional Fair Value Disclosure) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, book value	$ 52,715	$ 52,279
Long-term debt, fair value	52,676	55,331
Piedmont Natural Gas and Progress Energy [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unamortized debt discount (premium), net	1,700	1,700
Duke Energy Carolinas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, book value	10,394	10,103
Long-term debt, fair value	11,028	11,372
Progress Energy [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, book value	18,194	17,837
Long-term debt, fair value	19,357	20,000
Duke Energy Progress [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, book value	7,358	7,357
Long-term debt, fair value	7,527	7,992
Duke Energy Florida [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, book value	7,452	7,095
Long-term debt, fair value	7,945	7,953
Duke Energy Ohio [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, book value	2,066	2,067
Long-term debt, fair value	2,162	2,249
Duke Energy Indiana [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, book value	3,782	3,783
Long-term debt, fair value	4,223	4,464
Piedmont Natural Gas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, book value	2,037	2,037
Long-term debt, fair value	$ 2,087	$ 2,209