Fair Value Measurements (Additional Fair Value Disclosure) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, book value	$ 52,981	$ 52,279
Long-term debt, fair value	54,383	55,331
Duke Energy Carolinas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, book value	10,694	10,103
Long-term debt, fair value	11,556	11,372
Progress Energy [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, book value	17,757	17,837
Long-term debt, fair value	19,270	20,000
Duke Energy Progress [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, book value	7,357	7,357
Long-term debt, fair value	7,687	7,992
Duke Energy Florida [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, book value	7,015	7,095
Long-term debt, fair value	7,632	7,953
Duke Energy Ohio [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, book value	2,067	2,067
Long-term debt, fair value	2,217	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	4,322	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	$ 2,209	$ 2,209