Investments In Debt And Equity Securities (Available-For-Sale Investments) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Duke Energy Corp [Member]
Gross Unrealized Holding Gains	$ 631		$ 483
Gross Unrealized Holding Losses	(27)		(42)
Estimated Fair Value	2,858		2,549
NDTF [Member]
Gross Unrealized Holding Gains	616		473
Gross Unrealized Holding Losses	(9)		(22)
Estimated Fair Value	2,247		2,060
NDTF [Member] | U.S. Government Bonds [Member]
Gross Unrealized Holding Gains	11		16
Estimated Fair Value	285		306
NDTF [Member] | Other Debt Securities [Member]
Gross Unrealized Holding Gains	4		4
Gross Unrealized Holding Losses	(1)		(4)
Estimated Fair Value	171		161
NDTF [Member] | Equity Securities [Member]
Gross Unrealized Holding Gains	591		443
Gross Unrealized Holding Losses	(7)		(16)
Estimated Fair Value	1,518		1,337
NDTF [Member] | Corporate Debt Securities [Member]
Gross Unrealized Holding Gains	8		8
Gross Unrealized Holding Losses	(1)		(2)
Estimated Fair Value	222		205
NDTF [Member] | Municipal Bonds [Member]
Gross Unrealized Holding Gains	2		2
Estimated Fair Value	51		51
Grantor Trust [Member] | Duke Energy Indiana Grantor Trust [Member]
Gross Unrealized Holding Gains	10		6
Gross Unrealized Holding Losses			(1)
Estimated Fair Value	80		74
Grantor Trust [Member] | Equity Securities [Member] | Duke Energy Indiana Grantor Trust [Member]
Gross Unrealized Holding Gains	10		5
Gross Unrealized Holding Losses			(1)
Estimated Fair Value	52		46
Grantor Trust [Member] | Municipal Bonds [Member] | Duke Energy Indiana Grantor Trust [Member]
Gross Unrealized Holding Gains			1
Estimated Fair Value	28		28
Other Investments [Member]
Gross Unrealized Holding Gains	5		4
Gross Unrealized Holding Losses	(18)		(19)
Estimated Fair Value	531		415
Other Investments [Member] | Auction Rate Securities [Member]
Gross Unrealized Holding Gains		[1]
Gross Unrealized Holding Losses	(17)	[1]	(17)	[1]
Estimated Fair Value	72	[1]	71	[1]
Other Investments [Member] | Other Debt Securities [Member]
Gross Unrealized Holding Gains	1		2
Estimated Fair Value	83		68
Other Investments [Member] | Equity Securities [Member]
Gross Unrealized Holding Gains	1
Gross Unrealized Holding Losses			(1)
Estimated Fair Value	20		14
Other Investments [Member] | Corporate Debt Securities [Member]
Gross Unrealized Holding Gains	2		1
Gross Unrealized Holding Losses			(1)
Estimated Fair Value	299		241
Other Investments [Member] | U. S. Government Bonds [Member]
Gross Unrealized Holding Gains	1		1
Gross Unrealized Holding Losses	(1)
Estimated Fair Value	$ 57		$ 21

[1] At both March 31, 2012 and December 31, 2011, $12 million of these securities were held by Duke Energy Carolinas. Gross unrealized holding gains on these securities held by Duke Energy Carolinas were insignificant at both March 31, 2012 and December 31, 2011. Gross unrealized holding losses on these securities held by Duke Energy Carolinas were $3 million at both March 31, 2012 and December 31, 2011.