Investments in Debt and Equity Securities Investments in Debt and Equity Securities (Realized Gains and Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	$ 193	$ 271	$ 209
Realized losses	98	105	65
Duke Energy Carolinas [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	158	109	115
Realized losses	83	93	12
Progress Energy [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	33	157	90
Realized losses	13	11	46
Duke Energy Progress [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	26	19	58
Realized losses	11	5	26
Duke Energy Florida [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	7	138	32
Realized losses	$ 2	$ 5	$ 20