Investments in Debt and Equity Securities (Available-for-Sale Investments) (Details) (USD $) In Millions	Jun. 30, 2011		Dec. 31, 2010
Gross Unrealized Holding Gains	$ 564	[1]	$ 515	[1]
Gross Unrealized Holding Losses	(57)	[1]	(65)	[1]
Estimated Fair Value	2,498		2,401
Equity Securities [Member]
Gross Unrealized Holding Gains	537	[1]	481	[1]
Gross Unrealized Holding Losses	(19)	[1]	(16)	[1]
Estimated Fair Value	1,517		1,435
Corporate Debt Securities [Member]
Gross Unrealized Holding Gains	9	[1]	12	[1]
Gross Unrealized Holding Losses	(2)	[1]	(3)	[1]
Estimated Fair Value	256		270
Municipal Bonds [Member]
Gross Unrealized Holding Gains	1	[1]	1	[1]
Gross Unrealized Holding Losses	(8)	[1]	(9)	[1]
Estimated Fair Value	63		69
NDTF [Member]
Gross Unrealized Holding Gains	551		505
Gross Unrealized Holding Losses	(30)		(32)
U.S. Government Bonds [Member]
Gross Unrealized Holding Gains	11	[1]	10	[1]
Gross Unrealized Holding Losses			(1)	[1]
Estimated Fair Value	294		235
Auction Rate Securities [Member]
Gross Unrealized Holding Gains		[1],[2]		[1],[2]
Gross Unrealized Holding Losses	(26)	[1],[2]	(31)	[1],[2]
Estimated Fair Value	99	[2]	118	[2]
Other	90
Other short-term investments	9
Other Debt Securities [Member]
Gross Unrealized Holding Gains	6	[1]	11	[1]
Gross Unrealized Holding Losses	(2)	[1]	(5)	[1]
Estimated Fair Value	269		274
Duke Energy Indiana Grantor Trust [Member]
Gross Unrealized Holding Gains	$ 9		$ 6

[1] The table above includes unrealized gains and losses of $551 million and $30 million, respectively, at June 30, 2011 and unrealized gains and losses of $505 million and $32 million, respectively, at December 31, 2010 associated with investments held in the NDTF. Additionally, the table above includes unrealized gains of $9 million and an insignificant amount of unrealized losses, respectively, at June 30, 2011 and unrealized gains of $6 million and an insignificant amount of unrealized losses, respectively, at December 31, 2010 associated with investments held in the Duke Energy Indiana grantor trust. As discussed above, unrealized losses on investments within the NDTF and Duke Energy Indiana grantor trust are deferred as a regulatory asset pursuant to regulatory accounting treatment.

[2] At June 30, 2011, auction rate securities estimated fair value of $90 million are included in Other within Investments and Other Assets and estimated fair value of $9 million are classified as Short-Term Investments on the Condensed Consolidated Balance Sheets.