Fair Value Measurements (Additional Fair Value Disclosure) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 40,203	$ 40,020
Long-term debt, fair value	43,864	44,566
Duke Energy Carolinas [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	8,884	8,391
Long-term debt, fair value	9,860	9,626
Progress Energy [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	15,396	14,754
Long-term debt, fair value	17,146	16,951
Duke Energy Progress [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	6,851	6,201
Long-term debt, fair value	7,214	6,696
Duke Energy Florida [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	4,850	4,860
Long-term debt, fair value	5,585	5,767
Duke Energy Ohio [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	1,605	1,766
Long-term debt, fair value	1,766	1,970
Duke Energy Indiana [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	3,790	3,791
Long-term debt, fair value	$ 4,330	$ 4,456