Business Segments (Segments Assets) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Segment Assets	$ 112,008	$ 62,526
Duke Energy Ohio [Member]
Segment Assets	10,494	10,939
U.S. Franchised Electric And Gas [Member]
Segment Assets	96,919	47,977
Commercial Power [Member]
Segment Assets	6,897	6,939
International Energy [Member]
Segment Assets	4,790	4,539
Total Reportable Segments [Member]
Segment Assets	108,606	59,455
Total Reportable Segments [Member] | Duke Energy Ohio [Member]
Segment Assets	10,556	11,033
Other [Member]
Segment Assets	3,206	2,961
Other [Member] | Duke Energy Ohio [Member]
Segment Assets	110	259
Reclassifications [Member]
Segment Assets	196	110
Reclassifications [Member] | Duke Energy Ohio [Member]
Segment Assets	(172)	(353)
DEO Commercial Power [Member] | Duke Energy Ohio [Member]
Segment Assets	4,157	4,740
Franchised Electric & Gas [Member] | Duke Energy Ohio [Member]
Segment Assets	$ 6,399	$ 6,293