Investments in Debt and Equity Securities (Realized Gains and Losses)(Details) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	$ 82	$ 30	$ 200	$ 160
Realized losses	42	28	134	59
Duke Energy Carolinas [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	58	25	125	132
Realized losses	28	24	84	47
Progress Energy [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	21	5	71	26
Realized losses	13	4	49	10
Duke Energy Progress [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	18	4	60	21
Realized losses	11	3	42	8
Duke Energy Florida [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	3	1	11	5
Realized losses	$ 2	$ 1	$ 7	$ 2