Investments In Debt And Equity Securities (Unrealized Losses Of Available-For-Sale Debt And Equity Securities In A Continuous Loss Position) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Fair Value	$ 584	[1]	$ 440	[1]
Unrealized Loss Position greater than 12 months	(25)		(53)
Unrealized Loss Position less than 12 months	(17)		(12)
Duke Energy Indiana Grantor Trust [Member]
Fair value of investments	11		5
U.S. Government Bonds [Member]
Fair Value	8	[1]	38	[1]
Unrealized Loss Position less than 12 months			(1)
Auction Rate Securities [Member]
Fair Value	71	[1],[2]	118	[1],[2]
Unrealized Loss Position greater than 12 months	(17)	[2]	(31)	[2]
Other Debt Securities [Member]
Fair Value	121	[1]	84	[1]
Unrealized Loss Position greater than 12 months			(1)
Unrealized Loss Position less than 12 months	(4)		(3)
Equity Securities [Member]
Fair Value	123	[1]	85	[1]
Unrealized Loss Position greater than 12 months	(6)		(11)
Unrealized Loss Position less than 12 months	(12)		(5)
Corporate Debt Securities [Member]
Fair Value	258	[1]	73	[1]
Unrealized Loss Position greater than 12 months	(2)		(2)
Unrealized Loss Position less than 12 months	(1)		(2)
Municipal Bonds [Member]
Fair Value	3	[1]	42	[1]
Unrealized Loss Position greater than 12 months			(8)
Unrealized Loss Position less than 12 months			(1)
NDTF [Member]
Fair value of investments	$ 289		$ 226

[1] The table above includes fair values of $289 million and $226 million at December 31, 2011 and December 31, 2010, respectively, associated with investments held in the Duke Energy Carolinas NDTF. Additionally, the table above includes fair values of $11 million and $5 million at December 31, 2011 and December 31, 2010, respectively, associated with investments held in the Duke Energy Indiana grantor trust.

[2] See Note 15 for information about fair value measurements related to investments in auction rate debt securities.