Business Segments (Segments Assets) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Segment Assets	$ 61,799		$ 62,526
Duke Energy Carolinas [Member]
Segment Assets	29,356		29,896
Duke Energy Indiana [Member]
Segment Assets	9,876		10,062
U.S. Franchised Electric And Gas [Member]
Segment Assets	47,790		47,977
Commercial Power [Member]
Segment Assets	6,884		6,939
International Energy [Member]
Segment Assets	4,752		4,539
Total Reportable Segments [Member]
Segment Assets	59,426		59,455
Other [Member]
Segment Assets	2,337		2,961
Reclassifications [Member]
Segment Assets	$ 36	[1]	$ 110	[1]

[1] Primarily represents reclassification of federal tax balances in consolidation.