Investments in Debt and Equity Securities Investments in Debt and Equity Securities (Realized Gains and Losses) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	$ 271	$ 209	$ 117
Realized losses	105	65	19
Duke Energy Carolinas [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	109	115	89
Realized losses	93	12	6
Progress Energy [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	157	90	34
Realized losses	11	46	18
Duke Energy Progress [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	19	58	21
Realized losses	5	26	8
Duke Energy Florida [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	138	32	13
Realized losses	$ 5	$ 20	$ 9