Acquisitions and Sales of Other Assets (Purchase Price Calculation) (Details) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Jul. 02, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Progress Energy common shares outstanding	704,000,000		445,000,000	444,000,000	443,000,000
Exchange ratio	87.083%
Duke Energy common shares issued for Progress Energy common shares outstanding	257,867
Closing price of Duke Energy common shares		$ 69.84
Purchase price for common shares		$ 18,009
Fair value of outstanding earned stock compensation awards		62
Total estimated purchase price		$ 18,071
Progress Energy [Member]
Progress Energy common shares outstanding		296,116,000