Investments in Debt and Equity Securities (Realized Gains and Losses)(Details) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	$ 40	$ 64	$ 133	$ 118
Realized losses	37	42	99	92
Duke Energy Carolinas [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	24	33	90	67
Realized losses	23	19	63	56
Progress Energy [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	15	31	42	50
Realized losses	14	23	35	36
Duke Energy Progress [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	11	27	35	42
Realized losses	11	20	30	31
Duke Energy Florida [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	4	4	7	8
Realized losses	$ 3	$ 3	$ 5	$ 5