Quarterly Financial Data (Unusual or Infrequently Occurring Items) (Details) (USD $)	3 Months Ended							12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Voluntary severance program expense				$ (8,000,000)	$ (20,000,000)	$ (76,000,000)	$ (68,000,000)
Goodwill impairment charge						500,000,000			175,000,000	130,000,000
Energy efficiency revenue adjustment	59,000,000	[1]
Pre-tax impairment charge	(59,000,000)		(301,000,000)					335,000,000	726,000,000	420,000,000
Total				240,000,000	(64,000,000)	(736,000,000)	(68,000,000)
Gain on sale of equity investment								11,000,000	103,000,000	(21,000,000)
Deferred Revenue	59,000,000							59,000,000
Duke Energy Carolinas [Member]
Pre-tax impairment charge								12,000,000
Duke Energy Ohio [Member]
Pre-tax impairment charge								89,000,000	837,000,000	769,000,000
Duke Energy Indiana [Member]
Pre-tax impairment charge								234,000,000	44,000,000
Edwardsport IGCC Plant [Member]
Goodwill impairment charge			(222,000,000)
Pre-tax impairment charge					(44,000,000)
Emission Allowance [Member]
Goodwill impairment charge			(79,000,000)
DukeNet [Member]
Gain on sale of equity investment				139,000,000
Q-Comm Corporation [Member]
Gain on sale of equity investment				109,000,000
Commercial Power non-regulated Midwest generation [Member]
Goodwill impairment charge						(500,000,000)
Midwest generation asset and emission allowance [Member]
Goodwill impairment charge						$ (160,000,000)

[1] In the fourth quarter of 2011, Duke Energy recorded $59 million of previously deferred revenue resulting from the receipt of an order from the NCUC which allowed the recognition of revenue in excess of amounts billed to customers.