Investments in Debt and Equity Securities (Realized Gains and Losses)(Details) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	$ 102	$ 31
Realized losses	14	4
Duke Energy Carolinas [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	90	23
Realized losses	12	1
Progress Energy [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	12	7
Realized losses	1	2
Duke Energy Progress [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	9	6
Realized losses	1	2
Duke Energy Florida [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	3	1
Realized losses		$ 1