Condensed Consolidated Statements Of Member's Equity and Comprehensive Income - Carolinas (USD $) In Millions, unless otherwise specified	Duke Energy Carolinas [Member] Member's Equity [Member]	Duke Energy Carolinas [Member] Net Gains (Losses) on Cash Flow Hedges [Member]	Duke Energy Carolinas [Member] Other Equity [Member]	Duke Energy Carolinas [Member]	Net Gains (Losses) on Cash Flow Hedges [Member]	Other Equity [Member]	Total
Balance at Dec. 31, 2010	$ 8,938	$ (20)	$ (2)	$ 8,916
Net income	205			205			513
Other comprehensive income(loss), net of tax
Other comprehensive income					3	3	28
Balance at Mar. 31, 2011	9,143	(20)	(2)	9,121
Balance at Dec. 31, 2011	9,473	(17)	(2)	9,454
Net income	266			266			299
Other comprehensive income(loss), net of tax
Other comprehensive income					12		60
Balance at Mar. 31, 2012	$ 9,739	$ (17)	$ (2)	$ 9,720