Business Segments (Segments Assets) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Segment Assets	$ 63,031	$ 62,526
Duke Energy Ohio [Member]
Segment Assets	10,978	10,939
U.S. Franchised Electric And Gas [Member]
Segment Assets	48,451	47,977
Commercial Power [Member]
Segment Assets	7,268	6,939
International Energy [Member]
Segment Assets	4,678	4,539
Total Reportable Segments [Member]
Segment Assets	60,397	59,455
Total Reportable Segments [Member] | Duke Energy Ohio [Member]
Segment Assets	11,301	11,033
Other [Member]
Segment Assets	2,593	2,961
Other [Member] | Duke Energy Ohio [Member]
Segment Assets	142	259
Reclassifications [Member]
Segment Assets	41	110
Reclassifications [Member] | Duke Energy Ohio [Member]
Segment Assets	(465)	(353)
DEO Commercial Power [Member] | Duke Energy Ohio [Member]
Segment Assets	4,742	4,740
Franchised Electric & Gas [Member] | Duke Energy Ohio [Member]
Segment Assets	$ 6,559	$ 6,293